WorldWideScience

Sample records for dwarf-neutron star mergers

  1. Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity

    International Nuclear Information System (INIS)

    Paschalidis, Vasileios; MacLeod, Morgan; Baumgarte, Thomas W.; Shapiro, Stuart L.

    2009-01-01

    White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in the tidal disruption of the WD. The path a given binary will follow depends primarily on its mass ratio. We analyze the fate of known WDNS binaries and use population synthesis results to estimate the number of LISA-resolved galactic binaries that will undergo either SMT or UMT. We model the quasistationary SMT epoch by solving a set of simple ordinary differential equations and compute the corresponding gravitational waveforms. Finally, we discuss in general terms the possible fate of binaries that undergo UMT and construct approximate Newtonian equilibrium configurations of merged WDNS remnants. We use these configurations to assess plausible outcomes of our future, fully relativistic simulations of these systems. If sufficient WD debris lands on the NS, the remnant may collapse, whereby the gravitational waves from the inspiral, merger, and collapse phases will sweep from LISA through LIGO frequency bands. If the debris forms a disk about the NS, it may fragment and form planets.

  2. White Dwarfs, Neutron Stars and Black Holes

    Science.gov (United States)

    Szekeres, P.

    1977-01-01

    The three possible fates of burned-out stars: white dwarfs, neutron stars and black holes, are described in elementary terms. Characteristics of these celestial bodies, as provided by Einstein's work, are described. (CP)

  3. Head-on collisions of binary white dwarf-neutron stars: Simulations in full general relativity

    International Nuclear Information System (INIS)

    Paschalidis, Vasileios; Etienne, Zachariah; Liu, Yuk Tung; Shapiro, Stuart L.

    2011-01-01

    We simulate head-on collisions from rest at large separation of binary white dwarf-neutron stars (WDNSs) in full general relativity. Our study serves as a prelude to our analysis of the circular binary WDNS problem. We focus on compact binaries whose total mass exceeds the maximum mass that a cold-degenerate star can support, and our goal is to determine the fate of such systems. A fully general relativistic hydrodynamic computation of a realistic WDNS head-on collision is prohibitive due to the large range of dynamical time scales and length scales involved. For this reason, we construct an equation of state (EOS) which captures the main physical features of neutron stars (NSs) while, at the same time, scales down the size of white dwarfs (WDs). We call these scaled-down WD models 'pseudo-WDs (pWDs)'. Using pWDs, we can study these systems via a sequence of simulations where the size of the pWD gradually increases toward the realistic case. We perform two sets of simulations; One set studies the effects of the NS mass on the final outcome, when the pWD is kept fixed. The other set studies the effect of the pWD compaction on the final outcome, when the pWD mass and the NS are kept fixed. All simulations show that after the collision, 14%-18% of the initial total rest mass escapes to infinity. All remnant masses still exceed the maximum rest mass that our cold EOS can support (1.92M · ), but no case leads to prompt collapse to a black hole. This outcome arises because the final configurations are hot. All cases settle into spherical, quasiequilibrium configurations consisting of a cold NS core surrounded by a hot mantle, resembling Thorne-Zytkow objects. Extrapolating our results to realistic WD compactions, we predict that the likely outcome of a head-on collision of a realistic, massive WDNS system will be the formation of a quasiequilibrium Thorne-Zytkow-like object.

  4. Compact Objects in Astrophysics White Dwarfs, Neutron Stars and Black Holes

    CERN Document Server

    Camenzind, Max

    2007-01-01

    Compact objects are an important class of astronomical objects in current research. Supermassive black holes play an important role in the understanding of the formation of galaxies in the early Universe. Old white dwarfs are nowadays used to calibrate the age of the Universe. Mergers of neutron stars and black holes are the sources of intense gravitational waves which will be measured in the next ten years by gravitational wave detectors. Camenzind's Compact Objects in Astrophysics gives a comprehensive introduction and up-to-date overview about the physical processes behind these objects, covering the field from the beginning to most recent results, including all relevant observations. After a presentation of the taxonomy of compact objects, the basic principles of general relativity are given. The author then discusses in detail the physics and observations of white dwarfs and neutron stars (including the most recent equations of state for neutron star matter), the gravitational field of rapidly rotating c...

  5. Searching for Exoplanets around X-Ray Binaries with Accreting White Dwarfs, Neutron Stars, and Black Holes

    Science.gov (United States)

    Imara, Nia; Di Stefano, Rosanne

    2018-05-01

    We recommend that the search for exoplanets around binary stars be extended to include X-ray binaries (XRBs) in which the accretor is a white dwarf, neutron star, or black hole. We present a novel idea for detecting planets bound to such mass transfer binaries, proposing that the X-ray light curves of these binaries be inspected for signatures of transiting planets. X-ray transits may be the only way to detect planets around some systems, while providing a complementary approach to optical and/or radio observations in others. Any planets associated with XRBs must be in stable orbits. We consider the range of allowable separations and find that orbital periods can be hours or longer, while transit durations extend upward from about a minute for Earth-radius planets, to hours for Jupiter-radius planets. The search for planets around XRBs could begin at once with existing X-ray observations of these systems. If and when a planet is detected around an X-ray binary, the size and mass of the planet may be readily measured, and it may also be possible to study the transmission and absorption of X-rays through its atmosphere. Finally, a noteworthy application of our proposal is that the same technique could be used to search for signals from extraterrestrial intelligence. If an advanced exocivilization placed a Dyson sphere or similar structure in orbit around the accretor of an XRB in order to capture energy, such an artificial structure might cause detectable transits in the X-ray light curve.

  6. Special and general relativity with applications to white dwarfs, neutron stars and black holes

    CERN Document Server

    Glendenning, Norman K

    2007-01-01

    Special and General Relativity are concisely developed together with essential aspects of nuclear and particle physics. Problem sets are provided for many chapters, making the book ideal for a course on the physics of white dwarf and neutron star interiors.

  7. Binary neutron star merger simulations

    Energy Technology Data Exchange (ETDEWEB)

    Bruegmann, Bernd [Jena Univ. (Germany)

    2016-11-01

    Our research focuses on the numerical tools necessary to solve Einstein's equations. In recent years we have been particularly interested in spacetimes consisting of two neutron stars in the final stages of their evolution. Because of the emission of gravitational radiation, the objects are driven together to merge; the emitted gravitational wave signal is visualized. This emitted gravitational radiation carries energy and momentum away from the system and contains information about the system. Late last year the Laser Interferometer Gravitational-wave Observatory (LIGO) began searches for these gravitational wave signals at a sensitivity at which detections are expected. Although such systems can radiate a significant amount of their total mass-energy in gravitational waves, the gravitational wave signals one expects to receive on Earth are not strong, since sources of gravitational waves are often many millions of light years away. Therefore one needs accurate templates for the radiation one expects from such systems in order to be able to extract them out of the detector's noise. Although analytical models exist for compact binary systems when the constituents are well separated, we need numerical simulation to investigate the last orbits before merger to obtain accurate templates and validate analytical approximations. Due to the strong nonlinearity of the equations and the large separation of length scales, these simulations are computationally demanding and need to be run on large supercomputers. When matter is present the computational cost as compared to pure black hole (vacuum) simulations increases even more due to the additional matter fields. But also more interesting astrophysical phenomena can happen. In fact, there is the possibility for a strong electromagnetic signal from the merger (e.g., a short gamma-ray burst or lower-energy electromagnetic signatures from the ejecta) and significant neutrino emission. Additionally, we can expect that

  8. Double neutron stars: merger rates revisited

    Science.gov (United States)

    Chruslinska, Martyna; Belczynski, Krzysztof; Klencki, Jakub; Benacquista, Matthew

    2018-03-01

    We revisit double neutron star (DNS) formation in the classical binary evolution scenario in light of the recent Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo DNS detection (GW170817). The observationally estimated Galactic DNS merger rate of R_MW = 21^{+28}_{-14} Myr-1, based on three Galactic DNS systems, fully supports our standard input physics model with RMW = 24 Myr-1. This estimate for the Galaxy translates in a non-trivial way (due to cosmological evolution of progenitor stars in chemically evolving Universe) into a local (z ≈ 0) DNS merger rate density of Rlocal = 48 Gpc-3 yr-1, which is not consistent with the current LIGO/Virgo DNS merger rate estimate (1540^{+3200}_{-1220} Gpc-3 yr-1). Within our study of the parameter space, we find solutions that allow for DNS merger rates as high as R_local ≈ 600^{+600}_{-300} Gpc-3 yr-1 which are thus consistent with the LIGO/Virgo estimate. However, our corresponding BH-BH merger rates for the models with high DNS merger rates exceed the current LIGO/Virgo estimate of local BH-BH merger rate (12-213 Gpc-3 yr-1). Apart from being particularly sensitive to the common envelope treatment, DNS merger rates are rather robust against variations of several of the key factors probed in our study (e.g. mass transfer, angular momentum loss, and natal kicks). This might suggest that either common envelope development/survival works differently for DNS (˜10-20 M⊙ stars) than for BH-BH (˜40-100 M⊙ stars) progenitors, or high black hole (BH) natal kicks are needed to meet observational constraints for both types of binaries. Our conclusion is based on a limited number of (21) evolutionary models and is valid within this particular DNS and BH-BH isolated binary formation scenario.

  9. Discriminating strange star mergers from neutron star mergers by gravitational-wave measurements

    International Nuclear Information System (INIS)

    Bauswein, A.; Oechslin, R.; Janka, H.-T.

    2010-01-01

    We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave measurements. Self-binding of strange quark matter and the generally more compact stars yield features that clearly distinguish strange star from neutron star mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halo structures around the remnant as in the case of neutron star mergers, the coalescence of strange stars results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density strange quark matter disk. We also investigate the importance of including nonzero temperature equations of state in neutron star and strange star merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, e.g. the outer remnant structure and the delay time of the dense remnant core to black hole collapse depend on the inclusion of nonzero temperature effects. For comparing and classifying the gravitational-wave signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for strange star mergers. Only for particular choices of the equation of state the frequencies of neutron star and strange star mergers are similar. In such cases additional features of the gravitational-wave luminosity spectrum like the ratio of energy emitted during the inspiral phase to the energy radiated away in the postmerger stage may help to discriminate coalescence events of the different types. If such characteristic quantities could be extracted from gravitational-wave signals, for instance with the upcoming gravitational-wave detectors, a decision on the

  10. The Fate of Neutron Star Binary Mergers

    Energy Technology Data Exchange (ETDEWEB)

    Piro, Anthony L. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Giacomazzo, Bruno [Physics Department, University of Trento, via Sommarive 14, I-38123 Trento (Italy); Perna, Rosalba, E-mail: piro@carnegiescience.edu [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States)

    2017-08-01

    Following merger, a neutron star (NS) binary can produce roughly one of three different outcomes: (1) a stable NS, (2) a black hole (BH), or (3) a supramassive, rotationally supported NS, which then collapses to a BH following angular momentum losses. Which of these fates occur and in what proportion has important implications for the electromagnetic transient associated with the mergers and the expected gravitational wave (GW) signatures, which in turn depend on the high density equation of state (EOS). Here we combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected. For many EOSs, a significant fraction of the remnants are NSs or supramassive NSs. This lends support to scenarios in which a quickly spinning, highly magnetized NS may be powering an electromagnetic transient. This also indicates that it will be important for future GW observatories to focus on high frequencies to study the post-merger GW emission. Even in cases where individual GW events are too low in signal to noise to study the post merger signature in detail, the statistics of how many mergers produce NSs versus BHs can be compared with our work to constrain the EOS. To match short gamma-ray-burst (SGRB) X-ray afterglow statistics, we find that the stiffest EOSs are ruled out. Furthermore, many popular EOSs require a significant fraction of ∼60%–70% of SGRBs to be from NS–BH mergers rather than just binary NSs.

  11. Neutron Star Mergers and the R process

    Science.gov (United States)

    Joniak, Ronald; Ugalde, Claudio

    2017-09-01

    About half of the elements of the periodic table that are present today in the Solar System were synthesized before the formation of the Sun via a rapid neutron capture process (r process). However, the astrophysical site of the r process is a longstanding problem that has captivated both experimental and theoretical astrophysicists. Up to date, two possible scenarios for the site of the r process have been suggested: the first involves the high entropy wind of core collapse supernovae, and the second corresponds to the merger of two compact stellar objects such as neutron stars. We will study the robustness of the nucleosynthesis abundance pattern between the second and third r process peaks as produced by neutron star mergers with r process-like neutron exposures. First, we will vary parameters to obtain an understanding of the astrophysical mechanisms that create the r process. Next, we will create a program to obtain the best possible parameters based on a chi-squared test. Once we have the best fits, we will test the effect of fission in the overall isotope abundance pattern distribution. Later on, we will vary the ratio of masses of the two fission fragments and study its effect on elemental abundances. This research was supported by the UIC College of Liberal Arts and Sciences Undergraduate Research Initiative (LASURI).

  12. Merger of binary neutron stars: Gravitational waves and electromagnetic counterparts

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Masaru

    2016-12-15

    Late inspiral and merger phases of binary neutron stars are the valuable new experimental fields for exploring nuclear physics because (i) gravitational waves from them will bring information for the neutron-star equation of state and (ii) the matter ejected after the onset of the merger could be the main site for the r-process nucleosynthesis. We will summarize these aspects of the binary neutron stars, describing the current understanding for the merger process of binary neutron stars that has been revealed by numerical-relativity simulations.

  13. MERGER SIGNATURES IN THE DYNAMICS OF STAR-FORMING GAS

    International Nuclear Information System (INIS)

    Hung, Chao-Ling; Sanders, D. B.; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Martínez-Galarza, Juan R.; Zezas, Andreas; Lanz, Lauranne

    2016-01-01

    The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ∼0.2–0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ∼ 2–3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%–60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk

  14. Radioactively powered emission from black hole-neutron star mergers

    International Nuclear Information System (INIS)

    Tanaka, Masaomi; Wanajo, Shinya; Hotokezaka, Kenta; Kyutoku, Koutarou; Kiuchi, Kenta; Sekiguchi, Yuichiro; Shibata, Masaru

    2014-01-01

    Detection of the electromagnetic counterparts of gravitational wave (GW) sources is important to unveil the nature of compact binary coalescences. We perform three-dimensional, time-dependent, multi-frequency radiative transfer simulations for radioactively powered emission from the ejecta of black hole (BH)-neutron star (NS) mergers. Depending on the BH to NS mass ratio, spin of the BH, and equations of state of dense matter, BH-NS mergers can eject more material than NS-NS mergers. In such cases, radioactively powered emission from the BH-NS merger ejecta can be more luminous than that from NS-NS mergers. We show that, in spite of the expected larger distances to BH-NS merger events, the observed brightness of BH-NS mergers can be comparable to or even higher than that of NS-NS mergers. We find that, when the tidally disrupted BH-NS merger ejecta are confined to a small solid angle, the emission from BH-NS merger ejecta tends to be bluer than that from NS-NS merger ejecta for a given total luminosity. Thanks to this property, we might be able to distinguish BH-NS merger events from NS-NS merger events by multi-band observations of the radioactively powered emission. In addition to the GW observations, such electromagnetic observations can potentially provide independent information on the progenitors of GW sources and the nature of compact binary coalescences.

  15. Neutrino flavor evolution in neutron star mergers

    Science.gov (United States)

    Tian, James Y.; Patwardhan, Amol V.; Fuller, George M.

    2017-08-01

    We examine the flavor evolution of neutrinos emitted from the disklike remnant (hereafter called "neutrino disk") of a binary neutron star (BNS) merger. We specifically follow the neutrinos emitted from the center of the disk, along the polar axis perpendicular to the equatorial plane. We carried out two-flavor simulations using a variety of different possible initial neutrino luminosities and energy spectra and, for comparison, three-flavor simulations in specific cases. In all simulations, the normal neutrino mass hierarchy was used. The flavor evolution was found to be highly dependent on the initial neutrino luminosities and energy spectra; in particular, we found two broad classes of results depending on the sign of the initial net electron neutrino lepton number (i.e., the number of neutrinos minus the number of antineutrinos). In the antineutrino-dominated case, we found that the matter-neutrino resonance effect dominates, consistent with previous results, whereas in the neutrino-dominated case, a bipolar spectral swap develops. The neutrino-dominated conditions required for this latter result have been realized, e.g., in a BNS merger simulation that employs the "DD2" equation of state for neutron star matter [Phys. Rev. D 93, 044019 (2016), 10.1103/PhysRevD.93.044019]. For this case, in addition to the swap at low energies, a collective Mikheyev-Smirnov-Wolfenstein mechanism generates a high-energy electron neutrino tail. The enhanced population of high-energy electron neutrinos in this scenario could have implications for the prospects of r -process nucleosynthesis in the material ejected outside the plane of the neutrino disk.

  16. Star formation in mergers with comologically motivated initial conditions

    NARCIS (Netherlands)

    Karman, Wouter; Macciò, Andrea V.; Kannan, Rahul; Moster, Benjamin P.; Somerville, Rachel S.

    2015-01-01

    We use semi-analytic models and cosmological merger trees to provide the initial conditions for multimerger numerical hydrodynamic simulations, and exploit these simulations to explore the effect of galaxy interaction and merging on star formation (SF). We compute numerical realizations of 12 merger

  17. Modeling the Complete Gravitational Wave Spectrum of Neutron Star Mergers.

    Science.gov (United States)

    Bernuzzi, Sebastiano; Dietrich, Tim; Nagar, Alessandro

    2015-08-28

    In the context of neutron star mergers, we study the gravitational wave spectrum of the merger remnant using numerical relativity simulations. Postmerger spectra are characterized by a main peak frequency f2 related to the particular structure and dynamics of the remnant hot hypermassive neutron star. We show that f(2) is correlated with the tidal coupling constant κ(2)^T that characterizes the binary tidal interactions during the late-inspiral merger. The relation f(2)(κ(2)^T) depends very weakly on the binary total mass, mass ratio, equation of state, and thermal effects. This observation opens up the possibility of developing a model of the gravitational spectrum of every merger unifying the late-inspiral and postmerger descriptions.

  18. Hydrodynamic evolution of neutron star merger remnants

    Science.gov (United States)

    Liu, Men-Quan; Zhang, Jie

    2017-11-01

    Based on the special relativistic hydrodynamic equations and updated cooling function, we investigate the long-term evolution of neutron stars merger (NSM) remnants by a one-dimensional hydrodynamic code. Three NSM models from one soft equation of state, SFHo, and two stiff equations of state, DD2 and TM1, are used to compare their influences on the hydrodynamic evolution of remnants. We present the luminosity, mass and radius of remnants, as well as the velocity, temperature and density of shocks. For a typical interstellar medium (ISM) density with solar metallicity, we find that the NSM remnant from the SFHo model makes much more changes to ISM in terms of velocity, density and temperature distributions, compared with the case of DD2 and TM1 models. The maximal luminosity of the NSM remnant from the SFHo model is 3.4 × 1038 erg s-1, which is several times larger than that from DD2 and TM1 models. The NSM remnant from the SFHo model can maintain high luminosity (>1038 erg s-1) for 2.29 × 104 yr. Furthermore, the density and temperature of remnants at the maximal luminosity are not sensitive to the power of the original remnant. For the ISM with the solar metallicity and nH = 1 cm- 3, the density of the first shock ∼10-23 g cm-3 and the temperature ∼3 × 105 K in the maximal luminosity phase; The temperature of the first shock decreases and there is a thin 'dense' shell with density ∼10-21 g cm-3 after the maximal luminosity. These characteristics may be helpful for future observations of NSM remnants.

  19. Gravitational-Wave Luminosity of Binary Neutron Stars Mergers

    Science.gov (United States)

    Zappa, Francesco; Bernuzzi, Sebastiano; Radice, David; Perego, Albino; Dietrich, Tim

    2018-03-01

    We study the gravitational-wave peak luminosity and radiated energy of quasicircular neutron star mergers using a large sample of numerical relativity simulations with different binary parameters and input physics. The peak luminosity for all the binaries can be described in terms of the mass ratio and of the leading-order post-Newtonian tidal parameter solely. The mergers resulting in a prompt collapse to black hole have the largest peak luminosities. However, the largest amount of energy per unit mass is radiated by mergers that produce a hypermassive neutron star or a massive neutron star remnant. We quantify the gravitational-wave luminosity of binary neutron star merger events, and set upper limits on the radiated energy and the remnant angular momentum from these events. We find that there is an empirical universal relation connecting the total gravitational radiation and the angular momentum of the remnant. Our results constrain the final spin of the remnant black hole and also indicate that stable neutron star remnant forms with super-Keplerian angular momentum.

  20. Gravitational-Wave Luminosity of Binary Neutron Stars Mergers.

    Science.gov (United States)

    Zappa, Francesco; Bernuzzi, Sebastiano; Radice, David; Perego, Albino; Dietrich, Tim

    2018-03-16

    We study the gravitational-wave peak luminosity and radiated energy of quasicircular neutron star mergers using a large sample of numerical relativity simulations with different binary parameters and input physics. The peak luminosity for all the binaries can be described in terms of the mass ratio and of the leading-order post-Newtonian tidal parameter solely. The mergers resulting in a prompt collapse to black hole have the largest peak luminosities. However, the largest amount of energy per unit mass is radiated by mergers that produce a hypermassive neutron star or a massive neutron star remnant. We quantify the gravitational-wave luminosity of binary neutron star merger events, and set upper limits on the radiated energy and the remnant angular momentum from these events. We find that there is an empirical universal relation connecting the total gravitational radiation and the angular momentum of the remnant. Our results constrain the final spin of the remnant black hole and also indicate that stable neutron star remnant forms with super-Keplerian angular momentum.

  1. Multi-messenger Observations of a Binary Neutron Star Merger

    NARCIS (Netherlands)

    Scholten, Olaf; van den Berg, Adriaan

    2017-01-01

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A)

  2. Multi-messenger Observations of a Binary Neutron Star Merger

    DEFF Research Database (Denmark)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.

    2017-01-01

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 17081...

  3. Multi-messenger observations of a binary neutron star merger

    NARCIS (Netherlands)

    LIGO Scientific Collaboration and Virgo Collaboration; Fermi GBM; INTEGRAL; IceCube Collaboration; AstroSat Cadmium Zinc Telluride Imager Team; IPN Collaboration; The Insight-HXMT Collaboration; ANTARES Collaboration; The Swift Collaboration; AGILE Team; The 1M2H Team; The Dark Energy Camera GW-EM Collaboration and the DES Collaboration; The DLT40 Collaboration; GRAWITA: GRAvitational Wave Inaf TeAm; The Fermi Large Area Telescope Collaboration; ATCA: Australia Telescope Compact Array; ASKAP: Australian SKA Path finder; Las Cumbres Observatory Group; OzGrav; DWF (Deeper, Wider, Faster Program); AST3; CAASTRO Collaborations; The VINROUGE Collaboration; MASTER Collaboration; J-GEM; GROWTH; JAGWAR; Caltech- NRAO; TTU-NRAO; NuSTAR Collaborations; Pan-STARR; The MAXI Team; TZAC Consortium; KU Collaboration; Nordic Optical Telescope; ePESSTO; GROND; Texas Tech University; SALT Group; TOROS: Transient Robotic Observatory of the South Collaboration; The BOOTES Collaboration; MWA: Murchison Wide field Array; The CALET Collaboration; IKI-GW Follow-up Collaboration; H.E.S.S. Collaboration; LOFAR Collaboration; LWA: Long Wavelength Array; HAWC Collaboration; The Pierre Auger Collaboration; ALMA Collaboration; Euro VLBI Team; Pi of the Sky Collaboration; The Chandra Team at McGill University; DFN: Desert Fireball Network; ATLAS; High Time Resolution Universe Survey; RIMAS and RATIR; SKA South Africa / MeerKAT

    2017-01-01

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A)

  4. THE FATE OF THE COMPACT REMNANT IN NEUTRON STAR MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    Fryer, Chris L. [Department of Physics, The University of Arizona, Tucson, AZ 85721 (United States); Belczynski, Krzysztoff [Astronomical Observatory, University of Warsaw, Al Ujazdowskie 4, 00-478 Warsaw (Poland); Ramirez-Ruiz, Enrico [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Rosswog, Stephan [The Oskar klein Center, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Shen, Gang [Institute for Nuclear Theory, University of Washington, Seattle, WA 98195 (United States); Steiner, Andrew W. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States)

    2015-10-10

    Neutron star (binary neutron star and neutron star–black hole) mergers are believed to produce short-duration gamma-ray bursts (GRBs). They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and advanced VIRGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of Newtonian merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3–2.4 solar masses. If quick black hole formation is essential in producing GRBs, LIGO/Virgo observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

  5. The cosmic merger rate of neutron stars and black holes

    Science.gov (United States)

    Mapelli, Michela; Giacobbo, Nicola

    2018-06-01

    Six gravitational wave detections have been reported so far, providing crucial insights on the merger rate of double compact objects. We investigate the cosmic merger rate of double neutron stars (DNSs), neutron star-black hole binaries (NSBHs) and black hole binaries (BHBs) by means of population-synthesis simulations coupled with the Illustris cosmological simulation. We have performed six different simulations, considering different assumptions for the efficiency of common envelope (CE) ejection and exploring two distributions for the supernova (SN) kicks. The current BHB merger rate derived from our simulations spans from ˜150 to ˜240 Gpc-3 yr-1 and is only mildly dependent on CE efficiency. In contrast, the current merger rates of DNSs (ranging from ˜20 to ˜600 Gpc-3 yr-1) and NSBHs (ranging from ˜10 to ˜100 Gpc-3 yr-1) strongly depend on the assumptions on CE and natal kicks. The merger rate of DNSs is consistent with the one inferred from the detection of GW170817 only if a high efficiency of CE ejection and low SN kicks (drawn from a Maxwellian distribution with one dimensional root mean square σ = 15 km s-1) are assumed.

  6. Signatures of Heavy Element Production in Neutron Star Mergers

    Science.gov (United States)

    Barnes, Jennifer

    2018-06-01

    Compact object mergers involving at least one neutron star have long been theorized to be sites of astrophysical nucleosynthesis via rapid neutron capture (the r-process). The observation in light and gravitational waves of the first neutron star merger (GW1701817) this past summer provided a stunning confirmation of this theory. Electromagnetic emission powered by the radioactive decay of freshly synthesized nuclei from mergers encodes information about the composition burned by the r-process, including whether a particular merger event synthesized the heaviest nuclei along the r-process path, or froze out at lower mass number. However, efforts to model the emission in detail must still contend with many uncertainties. For instance, the uncertain nuclear masses far from the valley of stability influence the final composition burned by the r-process, as will weak interactions operating in the merger’s immediate aftermath. This in turn can affect the color electromagnetic emission. Understanding the details of these transients’ spectra will also require a detailed accounting the electronic transitions of r-process elements and ions, in order to identify the strong transitions that underlie spectral formation. This talk will provide an overview of our current understanding of radioactive transients from mergers, with an emphasis on the role of experiment in providing critical inputs for models and reducing uncertainty.

  7. Black Hole - Neutron Star Binary Mergers

    Data.gov (United States)

    National Aeronautics and Space Administration — Gravitational radiation waveforms for black hole-neutron star coalescence calculations. The physical input is Newtonian physics, an ideal gas equation of state with...

  8. Multi-messenger Observations of a Binary Neutron Star Merger

    DEFF Research Database (Denmark)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.

    2017-01-01

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A...... Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution....../optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A...

  9. Helicity coherence in binary neutron star mergers and nonlinear feedback

    Science.gov (United States)

    Chatelain, Amélie; Volpe, Cristina

    2017-02-01

    Neutrino flavor conversion studies based on astrophysical environments usually implement neutrino mixings, neutrino interactions with matter, and neutrino self-interactions. In anisotropic media, the most general mean-field treatment includes neutrino mass contributions as well, which introduce a coupling between neutrinos and antineutrinos termed helicity or spin coherence. We discuss resonance conditions for helicity coherence for Dirac and Majorana neutrinos. We explore the role of these mean-field contributions on flavor evolution in the context of a binary neutron star merger remnant. We find that resonance conditions can be satisfied in neutron star merger scenarios while adiabaticity is not sufficient for efficient flavor conversion. We analyze our numerical findings by discussing general conditions to have multiple Mikheyev-Smirnov-Wolfenstein-like resonances, in the presence of nonlinear feedback, in astrophysical environments.

  10. Neutron-Star Merger Detected By Many Eyes and Ears

    Science.gov (United States)

    Kohler, Susanna

    2017-10-01

    Where were you on Thursday, 17 August 2017? I was in Idaho, getting ready for Monday mornings solar eclipse. What I didnt know was that, at the time, around 70 teams around the world were mobilizing to point their ground- and space-based telescopes at a single patch of sky suspected to host the first gravitational-wave-detected merger of two neutron stars.Sudden Leaps for ScienceThe masses for black holes detected through electromagnetic observations (purple), black holes measured by gravitational-wave observations (blue), neutron stars measured with electromagnetic observations (yellow), and the neutron stars that merged in GW170817 (orange). [LIGO-Virgo/Frank Elavsky/NorthwesternUniversity]The process of science is long and arduous, generally occurring at a slow plod as theorists make predictions, and observations are then used to chip away at these theories, gradually confirming or disproving them. It is rare that science progresses forward in a giant leap, with years upon years of theories confirmed in one fell swoop.14 September 2015 marked the day of one such leap, as the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves for the first time simultaneously verifying that black holes exist, that black-hole binaries exist, and that they can merge on observable timescales, emitting signals that directly confirm the predictions of general relativity.As it turns out, 17 August 2017 was another such day. On this day, LIGO observed a gravitational-wave signal unlike its previous black-hole detections. Instead, this was a signal consistent with the merger of two neutron stars.Artists illustrations of the stellar-merger model for short gamma-ray bursts. In the model, 1) two neutron stars inspiral, 2) they merge and produce a gamma-ray burst, 3) a small fraction of their mass is flung out and radiates as a kilonova, 4) a massive neutron star or black hole with a disk remains after the event. [NASA, ESA, and A. Feild (STScI)]What We

  11. Binary neutron star mergers: a review of Einstein's richest laboratory.

    Science.gov (United States)

    Baiotti, Luca; Rezzolla, Luciano

    2017-09-01

    In a single process, the merger of binary neutron star systems combines extreme gravity, the copious emission of gravitational waves, complex microphysics and electromagnetic processes, which can lead to astrophysical signatures observable at the largest redshifts. We review here the recent progress in understanding what could be considered Einstein's richest laboratory, highlighting in particular the numerous significant advances of the last decade. Although special attention is paid to the status of models, techniques and results for fully general-relativistic dynamical simulations, a review is also offered on the initial data and advanced simulations with approximate treatments of gravity. Finally, we review the considerable amount of work carried out on the post-merger phase, including black-hole formation, torus accretion onto the merged compact object, the connection with gamma-ray burst engines, ejected material, and its nucleosynthesis.

  12. Electromagnetic Chirps from Neutron Star-Black Hole Mergers

    Science.gov (United States)

    Schnittman, Jeremy D.; Dal Canton, Tito; Camp, Jordan B.; Tsang, David; Kelly, Bernard J.

    2018-01-01

    We calculate the electromagnetic signal of a gamma-ray flare coming from the surface of a neutron star shortly before merger with a black hole companion. Using a new version of the Monte Carlo radiation transport code Pandurata that incorporates dynamic spacetimes, we integrate photon geodesics from the neutron star surface until they reach a distant observer or are captured by the black hole. The gamma-ray light curve is modulated by a number of relativistic effects, including Doppler beaming and gravitational lensing. Because the photons originate from the inspiraling neutron star, the light curve closely resembles the corresponding gravitational waveform: a chirp signal characterized by a steadily increasing frequency and amplitude. We propose to search for these electromagnetic chirps using matched filtering algorithms similar to those used in LIGO data analysis.

  13. Multi-messenger Observations of a Binary Neutron Star Merger

    International Nuclear Information System (INIS)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.

    2017-01-01

    Here, on 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg 2 at a luminosity distance of 40 −8 +8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M ⊙ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼9 and ∼16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

  14. Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

    Science.gov (United States)

    Shibata, Masaru; Kiuchi, Kenta

    2017-06-01

    Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

  15. Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

    Science.gov (United States)

    Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

    2014-01-01

    We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

  16. The Insignificance of Major Mergers in Driving Star Formation at z approximately equal to 2

    Science.gov (United States)

    Kaviraj, S.; Cohen, S.; Windhorst, R. A.; Silk, J.; O'Connell, R. W.; Dopita, M. A.; Dekel, A.; Hathi, N. P.; Straughn, A.; Rutkowski, M.

    2012-01-01

    We study the significance of major mergers in driving star formation in the early Universe, by quantifying the contribution of this process to the total star formation budget in 80 massive (M(*) > 10(exp 10) Solar M) galaxies at z approx = 2. Employing visually-classified morphologies from rest-frame V-band HST imaging, we find that 55(exp +/-14)% of the star formation budget is hosted by non-interacting late-types, with 27(exp +/-18% in major mergers and 18(exp +/- 6)% in spheroids. Given that a system undergoing a major merger continues to experience star formation driven by other processes at this epoch (e.g. cold accretion, minor mergers), approx 27% is a likely upper limit for the major-merger contribution to star formation activity at this epoch. The ratio of the average specific star formation rate in major mergers to that in the non-interacting late-types is approx 2.2:1, suggesting that the typical enhancement of star formation due to major merging is modest and that just under half the star formation in systems experiencing major mergers is unrelated to the merger itself. Taking this into account, we estimate that the actual major-merger contribution to the star formation budget may be as low as approx 15%. While our study does not preclude a major-merger-dominated. era in the very early Universe, if the major-merger contribution to star formation does not evolve significantly into larger look-back times, then this process has a relatively insignificant role in driving stellar mass assembly over cosmic time.

  17. Properties of Kilonovae from Dynamical and Post-merger Ejecta of Neutron Star Mergers

    Science.gov (United States)

    Tanaka, Masaomi; Kato, Daiji; Gaigalas, Gediminas; Rynkun, Pavel; Radžiūtė, Laima; Wanajo, Shinya; Sekiguchi, Yuichiro; Nakamura, Nobuyuki; Tanuma, Hajime; Murakami, Izumi; Sakaue, Hiroyuki A.

    2018-01-01

    Ejected material from neutron star mergers gives rise to electromagnetic emission powered by radioactive decays of r-process nuclei, the so-called kilonova or macronova. While properties of the emission are largely affected by opacities in the ejected material, available atomic data for r-process elements are still limited. We perform atomic structure calculations for r-process elements: Se (Z = 34), Ru (Z = 44), Te (Z = 52), Ba (Z = 56), Nd (Z = 60), and Er (Z = 68). We confirm that the opacities from bound–bound transitions of open f-shell, lanthanide elements (Nd and Er) are higher than those of the other elements over a wide wavelength range. The opacities of open s-shell (Ba), p-shell (Se and Te), and d-shell (Ru) elements are lower than those of open f-shell elements, and their transitions are concentrated in the ultraviolet and optical wavelengths. We show that the optical brightness can be different by > 2 mag depending on the element abundances in the ejecta such that post-merger, lanthanide-free ejecta produce brighter and bluer optical emission. Such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small. For the ejecta mass of 0.01 {M}ȯ , observed magnitudes of the blue emission will reach 21.0 mag (100 Mpc) and 22.5 mag (200 Mpc) in the g and r bands within a few days after the merger, which are detectable with 1 m or 2 m class telescopes.

  18. GRB 130603B: No Compelling Evidence for Neutron Star Merger

    Directory of Open Access Journals (Sweden)

    Shlomo Dado

    2015-01-01

    Full Text Available The near infrared (NIR flare/rebrightening in the afterglow of the short hard gamma ray burst (SHB 130603B measured with the Hubble Space Telescope (HST and an alleged late-time X-ray excess were interpreted as possible evidence of a neutron star merger origin of SHBs. However, the X-ray afterglow that was measured with the Swift XRT and Newton XMM has the canonical behaviour of a synchrotron afterglow produced by a highly relativistic jet. The H-band flux observed with HST 9.41 days after burst is that expected from the measured late-time X-ray afterglow. The late-time flare/rebrightening of the NIR-optical afterglow of SHB 130603B could have been produced also by jet collision with an interstellar density bump. Moreover, SHB plus a kilonova can be produced also by the collapse of a compact star (neutron star, strange star, or quark star to a more compact object due to cooling, loss of angular momentum, or mass accretion.

  19. Numerical simulation of binary black hole and neutron star mergers

    Energy Technology Data Exchange (ETDEWEB)

    Kastaun, W.; Rezzolla, L. [Albert Einstein Institut, Potsdam-Golm (Germany)

    2016-11-01

    One of the last predictions of general relativity that still awaits direct observational confirmation is the existence of gravitational waves. Those fluctuations of the geometry of space and time are expected to travel with the speed of light and are emitted by any accelerating mass. Only the most violent events in the universe, such as mergers of two black holes or neutron stars, produce gravitational waves strong enough to be measured. Even those waves are extremely weak when arriving at Earth, and their detection is a formidable technological challenge. In recent years sufficiently sensitive detectors became operational, such as GEO600, Virgo, and LIGO. They are expected to observe around 40 events per year. To interpret the observational data, theoretical modeling of the sources is a necessity, and requires numerical simulations of the equations of general relativity and relativistic hydrodynamics. Such computations can only be carried out on large scale supercomputers, given that many scenarios need to be simulated, each of which typically occupies hundreds of CPU cores for a week. Our main goal is to predict the gravitational wave signal from the merger of two compact objects. Comparison with future observations will provide important insights into the fundamental forces of nature in regimes that are impossible to recreate in laboratory experiments. The waveforms from binary black hole mergers would allow one to test the correctness of general relativity in previously inaccessible regimes. The signal from binary neutron star mergers will provide input for nuclear physics, because the signal depends strongly on the unknown properties of matter at the ultra high densities inside neutron stars, which cannot be observed in any other astrophysical scenario. Besides mergers, we also want to improve the theoretical models of close encounters between black holes. A gravitational wave detector with even higher sensitivity, the Einstein Telescope, is already in the

  20. RCB stars from double degenerate white dwarf mergers

    Science.gov (United States)

    Staff, Jan; Wiggins, Brandon K.; Marcello, Dominic; Motl, Patrick; Clayton, Geoffrey C.

    2018-01-01

    We have conducted grid based and SPH based hydrodynamic simulations of white dwarf mergers, to investigate the role of dredge-up and mixing during the merger. The goal is to test if sufficiently little 16O can be brought up to the surface to explain the observed 16O to 18O ratio of order unity found in RCB stars. In all simulations, the total mass is ~< 1 M⊙. By initializing both the grid based and the SPH simulations with the same setup, we can compare the results from these different methods. In most of the simulations, more than 0.01 M⊙ of 16O is brought up to the surface. Hence a similar mass of 18O must be produced in order to explain the observed oxygen ratio. However,in SPH simulations where the accretor is a hybrid He/CO white dwarf, much less 16O is brought to the surface, making this an excellent candidate for the progenitor of RCB stars.

  1. Measuring neutron-star properties via gravitational waves from neutron-star mergers.

    Science.gov (United States)

    Bauswein, A; Janka, H-T

    2012-01-06

    We demonstrate by a large set of merger simulations for symmetric binary neutron stars (NSs) that there is a tight correlation between the frequency peak of the postmerger gravitational-wave (GW) emission and the physical properties of the nuclear equation of state (EoS), e.g., expressed by the radius of the maximum-mass Tolman-Oppenheimer-Volkhoff configuration. Therefore, a single measurement of the peak frequency of the postmerger GW signal will constrain the NS EoS significantly. For optimistic merger-rate estimates a corresponding detection with Advanced LIGO is expected to happen within an operation time of roughly a year.

  2. Numerical relativity simulations of precessing binary neutron star mergers

    Science.gov (United States)

    Dietrich, Tim; Bernuzzi, Sebastiano; Brügmann, Bernd; Ujevic, Maximiliano; Tichy, Wolfgang

    2018-03-01

    We present the first set of numerical relativity simulations of binary neutron mergers that include spin precession effects and are evolved with multiple resolutions. Our simulations employ consistent initial data in general relativity with different spin configurations and dimensionless spin magnitudes ˜0.1 . They start at a gravitational-wave frequency of ˜392 Hz and cover more than 1 precession period and about 15 orbits up to merger. We discuss the spin precession dynamics by analyzing coordinate trajectories, quasilocal spin measurements, and energetics, by comparing spin aligned, antialigned, and irrotational configurations. Gravitational waveforms from different spin configuration are compared by calculating the mismatch between pairs of waveforms in the late inspiral. We find that precession effects are not distinguishable from nonprecessing configurations with aligned spins for approximately face-on binaries, while the latter are distinguishable from nonspinning configurations. Spin precession effects are instead clearly visible for approximately edge-on binaries. For the parameters considered here, precession does not significantly affect the characteristic postmerger gravitational-wave frequencies nor the mass ejection. Our results pave the way for the modeling of spin precession effects in the gravitational waveform from binary neutron star events.

  3. Search for Post-merger Gravitational Waves from the Remnant of the Binary Neutron Star Merger GW170817

    NARCIS (Netherlands)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Afrough, M.; Agarwal, B.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allen, G.; Allocca, A.; Altin, P. A.; Amato, A.; Ananyeva, A.; Anderson, S. B.; Anderson, W. G.; Angelova, S. V.; Antier, S.; Appert, S.; Arai, K.; Araya, M. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Atallah, D. V.; Aufmuth, P.; Aulbert, C.; AultONeal, K.; Austin, C.; Avila-Alvarez, A.; Babak, S.; Bacon, P.; Bader, M. K. M.; Bae, S.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Banagiri, S.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barkett, K.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Bawaj, M.; Bayley, J. C.; Bazzan, M.; Becsy, B.; Beer, C.; Bejger, M.; Belahcene, I.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Bernuzzi, S.; Bero, J. J.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Billman, C. R.; Birch, J.; Birney, R.; Birnholtz, O.; Biscans, S.; Biscoveanu, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blackman, J.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bode, N.; Boer, M.; Bogaert, G.; Bohe, A.; Bondu, F.; Bonilla, E.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bossie, K.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Bustillo, J. Calderon; Callister, T. A.; Calloni, E.; Camp, J. B.; Canepa, M.; Canizares, P.; Cannon, K. C.; Cao, H.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Carney, M. F.; Diaz, J. Casanueva; Casentini, C.; Caudill, S.; Cavaglia, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerda-Duran, P.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chase, E.; Chassande-Mottin, E.; Chatterjee, D.; Cheeseboro, B. D.; Chen, H. Y.; Chen, X.; Chen, Y.; Cheng, H. -P.; Chia, H.; Chincarini, A.; Chiummo, A.; Chmiel, T.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, A. J. K.; Chua, S.; Chung, A. K. W.; Chung, S.; Ciani, G.; Ciolfi, R.; Cirelli, C. E.; Cirone, A.; Clara, F.; Clark, J. A.; Clearwater, P.; Cleva, F.; Cocchieri, C.; Coccia, E.; Cohadon, P. -F.; Cohen, D.; Colla, A.; Collette, C. G.; Cominsky, L. R.; Constancio, M., Jr.; Conti, L.; Cooper, S. J.; Corban, P.; Corbitt, T. R.; Cordero-Carrion, I.; Corley, K. R.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J. -P.; Countryman, S. T.; Couvares, P.; Covas, P. B.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Creighton, J. D. E.; Creighton, T. D.; Cripe, J.; Crowder, S. G.; Cullen, T. J.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Dalya, G.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dasgupta, A.; Costa, C. F. Da Silva; Dattilo, V.; Dave, I.; Davier, M.; Davis, D.; Daw, E. J.; Day, B.; De, S.; DeBra, D.; Degallaix, J.; De Laurentis, M.; Deleglise, S.; Del Pozzo, W.; Demos, N.; Denker, T.; Dent, T.; De Pietri, R.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; De Rossi, C.; DeSalvo, R.; de Varona, O.; Devenson, J.; Dhurandhar, S.; Diaz, M. C.; Dietrich, T.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Renzo, F.; Doctor, Z.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Dorrington, I.; Douglas, R.; Alvarez, M. Dovale; Downes, T. P.; Drago, M.; Dreissigacker, C.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dupej, P.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H. -B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Eisenstein, R. A.; Essick, R. C.; Estevez, D.; Etienne, Z. B.; Etzel, T.; Evans, M.; Evans, T. M.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Farinon, S.; Farr, B.; Farr, W. M.; Fauchon-Jones, E. J.; Favata, M.; Fays, M.; Fee, C.; Fehrmann, H.; Feicht, J.; Fejer, M. M.; Fernandez-Galiana, A.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Finstad, D.; Fiori, I.; Fiorucci, D.; Fishbach, M.; Fisher, R. P.; Fitz-Axen, M.; Flaminio, R.; Fletcher, M.; Flynn, E.; Fong, H.; Font, J. A.; Forsyth, P. W. F.; Forsyth, S. S.; Fournier, J. -D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fries, E. M.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H.; Gadre, B. U.; Gaebel, S. M.; Gair, J. R.; Gammaitoni, L.; Ganija, M. R.; Gaonkar, S. G.; Garcia-Quiros, C.; Garufi, F.; Gateley, B.; Gaudio, S.; Gaur, G.; Gayathri, V.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; George, D.; George, J.; Gergely, L.; Germain, V.; Ghonge, S.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glover, L.; Goetz, E.; Goetz, R.; Gomes, S.; Goncharov, B.; Gonzalez, G.; Castro, J. M. Gonzalez; Gopakumar, A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Gretarsson, E. M.; Groot, P.; Grote, H.; Grunewald, S.; Gruning, P.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Halim, O.; Hall, B. R.; Hall, E. D.; Hamilton, E. Z.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hannuksela, O. A.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Haster, C. -J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hinderer, T.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Horst, C.; Hough, J.; Houston, E. A.; Howell, E. J.; Hreibi, A.; Hu, Y. M.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Inta, R.; Intini, G.; Isa, H. N.; Isac, J. -M.; Isi, M.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jimenez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Junker, J.; Kalaghatgi, C. V.; Kalogera, V.; Kamai, B.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Kastaun, W.; Katolik, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kawabe, K.; Kefelian, F.; Keitel, D.; Kemball, A. J.; Kennedy, R.; Kent, C.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J. C.; Kim, K.; Kim, W.; Kim, W. S.; Kim, Y. -M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kinley-Hanlon, M.; Kirchhoff, R.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Knowles, T. D.; Koch, P.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kraemer, C.; Kringel, V.; Krishnan, B.; Krolak, A.; Kuehn, G.; Kumar, P.; Kumar, R.; Kumar, S.; Kuo, L.; Kutynia, A.; Kwang, S.; Lackey, B. D.; Lai, K. H.; Landry, M.; Lang, R. N.; Lange, J.; Lantz, B.; Lanza, R. K.; Lartaux-Vollard, A.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, H. W.; Lee, K.; Lehmann, J.; Lenon, A.; Leonardi, M.; Leroy, N.; Letendre, N.; Levin, Y.; Li, T. G. F.; Linker, S. D.; Liu, J.; Lo, R. K. L.; Lockerbie, N. A.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lousto, C. O.; Lovelace, G.; Lueck, H.; Lumaca, D.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macas, R.; Macfoy, S.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Hernandez, I. Magana; Magana-Sandoval, F.; Zertuche, L. Magana; Magee, R. M.; Majorana, E.; Maksimovic, I.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marka, S.; Marka, Z.; Markakis, C.; Markosyan, A. S.; Markowitz, A.; Maros, E.; Marquina, A.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Mason, K.; Massera, E.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matas, A.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McCuller, L.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McNeill, L.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Mejuto-Villa, E.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, B. B.; Miller, J.; Milovich-Goff, M. C.; Minazzoli, O.; Minenkov, Y.; Ming, J.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moffa, D.; Moggi, A.; Mogushi, K.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Muniz, E. A.; Muratore, M.; Murray, P. G.; Napier, K.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Neilson, J.; Nelemans, G.; Nelson, T. J. N.; Nery, M.; Neunzert, A.; Nevin, L.; Newport, J. M.; Newton, G.; Ng, K. K. Y.; Nguyen, T. T.; Nichols, D.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Noack, A.; Nocera, F.; Nolting, D.; North, C.; Nuttall, L. K.; Oberling, J.; O'Dea, G. D.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Okada, M. A.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; Ormiston, R.; Ortega, L. F.; O'Shaughnessy, R.; Ossokine, S.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pace, A. E.; Page, J.; Page, M. A.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, Howard; Pan, Huang-Wei; Pang, B.; Pang, P. T. H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Parida, A.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patil, M.; Patricelli, B.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perez, C. J.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Phukon, K. S.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pirello, M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Porter, E. K.; Post, A.; Powell, J.; Prasad, J.; Pratt, J. W. W.; Pratten, G.; Predoi, V.; Prestegard, T.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L. G.; Puncken, O.; Punturo, M.; Puppo, P.; Puerrer, M.; Qi, H.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rajbhandari, B.; Rakhmanov, M.; Ramirez, K. E.; Ramos-Buades, A.; Rapagnani, P.; Raymond, V.; Razzano, M.; Read, J.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Ren, W.; Reyes, S. D.; Ricci, F.; Ricker, P. M.; Rieger, S.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romel, C. L.; Romie, J. H.; Rosinska, D.; Ross, M. P.; Rowan, S.; Ruediger, A.; Ruggi, P.; Rutins, G.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sampson, L. M.; Sanchez, E. J.; Sanchez, L. E.; Sanchis-Gual, N.; Sandberg, V.; Sanders, J. R.; Sarin, N.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Scheel, M.; Scheuer, J.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schoenbeck, A.; Schreiber, E.; Schuette, D.; Schulte, B. W.; Schutz, B. F.; Schwalbe, S. G.; Scott, J.; Scott, S. M.; Seidel, E.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Shaddock, D. A.; Shaffer, T. J.; Shah, A. A.; Shahriar, M. S.; Shaner, M. B.; Shao, L.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, L. P.; Singh, A.; Singhal, A.; Sintes, A. M.; Rana, J.; Slagmolen, B. J. J.; Smith, B.; Smith, R. J. E.; Smith, R. J. E.; Somala, S.; Son, E. J.; Sonnenberg, J. A.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Sowell, E.; Spencer, A. P.; Srivastava, A. K.; Staats, K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stevenson, S. P.; Stone, R.; Stops, D. J.; Strain, K. A.; Stratta, G.; Strigin, S. E.; Strunk, A.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Suresh, J.; Sutton, P. J.; Swinkels, B. L.; Szczepanczyk, M. J.; Tacca, M.; Tait, S. C.; Talbot, C.; Talukder, D.; Tanner, D. B.; Tapai, M.; Taracchini, A.; Tasson, J. D.; Taylor, J. A.; Taylor, R.; Tewari, S. V.; Theeg, T.; Thies, F.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tonelli, M.; Tornasi, Z.; Torres-Forne, A.; Torrie, C. I.; Toyra, D.; Travasso, F.; Traylor, G.; Trinastic, J.; Tringali, M. C.; Trozzo, L.; Tsang, K. W.; Tse, M.; Tso, R.; Tsukada, L.; Tsuna, D.; Tuyenbayev, D.; Ueno, K.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Varma, V.; Vass, S.; Vasuth, M.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Venugopalan, G.; Verkindt, D.; Vetrano, F.; Vicere, A.; Viets, A. D.; Vinciguerra, S.; Vine, D. J.; Vinet, J. -Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walet, R.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, J. Z.; Wang, W. H.; Wang, Y. F.; Ward, R. L.; Warner, J.; Was, M.; Watchi, J.; Weaver, B.; Wei, L. -W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wessel, E. K.; Wessels, P.; Westerweck, J.; Westphal, T.; Wette, K.; Whelan, J. T.; White, D. D.; Whiting, B. F.; Whittle, C.; Wilken, D.; Williams, D.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Wofford, J.; Wong, K. W. K.; Worden, J.; Wright, J. L.; Wu, D. S.; Wysocki, D. M.; Xiao, S.; Yamamoto, H.; Yancey, C. C.; Yang, L.; Yap, M. J.; Yazback, M.; Yu, Hang; Yu, Haocun; Yvert, M.; Zadrozny, A.; Zanolin, M.; Zelenova, T.; Zendri, J. -P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, T.; Zhang, Y. -H.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, S. J.; Zhu, X. J.; Zimmerman, A. B.; Zucker, M. E.; Zweizig, J.

    2017-01-01

    The first observation of a binary neutron star (NS) coalescence by the Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors offers an unprecedented opportunity to study matter under the most extreme conditions. After such a merger, a compact remnant is left over whose nature depends

  4. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xianfei; Bi, Shaolan [Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Hall, Philip D.; Jeffery, C. Simon, E-mail: zxf@bnu.edu.cn [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom)

    2017-02-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  5. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    International Nuclear Information System (INIS)

    Zhang, Xianfei; Bi, Shaolan; Hall, Philip D.; Jeffery, C. Simon

    2017-01-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  6. Advanced LIGO constraints on neutron star mergers and r-process sites

    International Nuclear Information System (INIS)

    Côté, Benoit; Belczynski, Krzysztof; Fryer, Chris L.; Ritter, Christian

    2017-01-01

    The role of compact binary mergers as the main production site of r-process elements is investigated by combining stellar abundances of Eu observed in the Milky Way, galactic chemical evolution (GCE) simulations, and binary population synthesis models, and gravitational wave measurements from Advanced LIGO. We compiled and reviewed seven recent GCE studies to extract the frequency of neutron star–neutron star (NS–NS) mergers that is needed in order to reproduce the observed [Eu/Fe] versus [Fe/H] relationship. We used our simple chemical evolution code to explore the impact of different analytical delay-time distribution functions for NS–NS mergers. We then combined our metallicity-dependent population synthesis models with our chemical evolution code to bring their predictions, for both NS–NS mergers and black hole–neutron star mergers, into a GCE context. Finally, we convolved our results with the cosmic star formation history to provide a direct comparison with current and upcoming Advanced LIGO measurements. When assuming that NS–NS mergers are the exclusive r-process sites, and that the ejected r-process mass per merger event is 0.01 M_⊙, the number of NS–NS mergers needed in GCE studies is about 10 times larger than what is predicted by standard population synthesis models. Here, these two distinct fields can only be consistent with each other when assuming optimistic rates, massive NS–NS merger ejecta, and low Fe yields for massive stars. For now, population synthesis models and GCE simulations are in agreement with the current upper limit (O1) established by Advanced LIGO during their first run of observations. Upcoming measurements will provide an important constraint on the actual local NS–NS merger rate, will provide valuable insights on the plausibility of the GCE requirement, and will help to define whether or not compact binary mergers can be the dominant source of r-process elements in the universe.

  7. Search for dark matter effects on gravitational signals from neutron star mergers

    Science.gov (United States)

    Ellis, John; Hektor, Andi; Hütsi, Gert; Kannike, Kristjan; Marzola, Luca; Raidal, Martti; Vaskonen, Ville

    2018-06-01

    Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components.

  8. arXiv Search for Dark Matter Effects on Gravitational Signals from Neutron Star Mergers

    CERN Document Server

    Ellis, John; Hütsi, Gert; Kannike, Kristjan; Marzola, Luca; Raidal, Martti; Vaskonen, Ville

    2018-06-10

    Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components.

  9. Search for dark matter effects on gravitational signals from neutron star mergers

    OpenAIRE

    Ellis, John; Hektor, Andi; Hütsi, Gert; Kannike, Kristjan; Marzola, Luca; Raidal, Martti; Vaskonen, Ville

    2018-01-01

    Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components.

  10. Searching for dark matter with neutron star mergers and quiet kilonovae

    Science.gov (United States)

    Bramante, Joseph; Linden, Tim; Tsai, Yu-Dai

    2018-03-01

    We identify new astrophysical signatures of dark matter that implodes neutron stars (NSs), which could decisively test whether NS-imploding dark matter is responsible for missing pulsars in the Milky Way galactic center, the source of some r -process elements, and the origin of fast-radio bursts. First, NS-imploding dark matter forms ˜10-10 solar mass or smaller black holes inside neutron stars, which proceed to convert neutron stars into ˜1.5 solar mass black holes (BHs). This decreases the number of neutron star mergers seen by LIGO/Virgo (LV) and associated merger kilonovae seen by telescopes like DES, BlackGEM, and ZTF, instead producing a population of "black mergers" containing ˜1.5 solar mass black holes. Second, dark matter-induced neutron star implosions may create a new kind of kilonovae that lacks a detectable, accompanying gravitational signal, which we call "quiet kilonovae." Using DES data and the Milky Way's r-process abundance, we constrain quiet kilonovae. Third, the spatial distribution of neutron star merger kilonovae and quiet kilonovae in galaxies can be used to detect dark matter. NS-imploding dark matter destroys most neutron stars at the centers of disc galaxies, so that neutron star merger kilonovae would appear mostly in a donut at large radii. We find that as few as ten neutron star merger kilonova events, located to ˜1 kpc precision could validate or exclude dark matter-induced neutron star implosions at 2 σ confidence, exploring dark matter-nucleon cross-sections 4-10 orders of magnitude below current direct detection experimental limits. Similarly, NS-imploding dark matter as the source of fast radio bursts can be tested at 2 σ confidence once 20 bursts are located in host galaxies by radio arrays like CHIME and HIRAX.

  11. R -process Element Cosmic Rays from Neutron Star Mergers

    Energy Technology Data Exchange (ETDEWEB)

    Komiya, Yutaka; Shigeyama, Toshikazu [Research Center for the Early Universe, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, 113-0033, Tokyo (Japan)

    2017-09-10

    Neutron star mergers (NSMs) are one of the most plausible sources of r -process elements in the universe. Therefore, NSMs can also be a major source of ultra-heavy elements in cosmic rays. In this paper, we first estimate the contribution of r -process elements synthesized in NSMs to the ultra-heavy element cosmic rays (UHCRs) by calculating transport equations that take into account energy loss processes and spallations. We show that the flux of UHCRs accelerated by the NSMs themselves fluctuates by many orders of magnitude on a timescale of several million years and can overwhelm UHCRs accelerated by supernova remnants (SNRs) after an NSM takes place within a few kiloparsec from the solar system. Experiments with very long exposure times using meteorites as UHCR detectors can detect this fluctuation. As a consequence, we show that if NSMs are the primary source of UHCRs, future experiments using meteorites may be able to reveal the event history of NSMs in the solar vicinity. We also describe a possible difference in the abundance pattern and energy spectrum of UHCRs between NSM and SNR accelerations.

  12. General relativistic magnetohydrodynamic simulations of binary neutron star mergers forming a long-lived neutron star

    Science.gov (United States)

    Ciolfi, Riccardo; Kastaun, Wolfgang; Giacomazzo, Bruno; Endrizzi, Andrea; Siegel, Daniel M.; Perna, Rosalba

    2017-03-01

    Merging binary neutron stars (BNSs) represent the ultimate targets for multimessenger astronomy, being among the most promising sources of gravitational waves (GWs), and, at the same time, likely accompanied by a variety of electromagnetic counterparts across the entire spectrum, possibly including short gamma-ray bursts (SGRBs) and kilonova/macronova transients. Numerical relativity simulations play a central role in the study of these events. In particular, given the importance of magnetic fields, various aspects of this investigation require general relativistic magnetohydrodynamics (GRMHD). So far, most GRMHD simulations focused the attention on BNS mergers leading to the formation of a hypermassive neutron star (NS), which, in turn, collapses within few tens of ms into a black hole surrounded by an accretion disk. However, recent observations suggest that a significant fraction of these systems could form a long-lived NS remnant, which will either collapse on much longer time scales or remain indefinitely stable. Despite the profound implications for the evolution and the emission properties of the system, a detailed investigation of this alternative evolution channel is still missing. Here, we follow this direction and present a first detailed GRMHD study of BNS mergers forming a long-lived NS. We consider magnetized binaries with different mass ratios and equations of state and analyze the structure of the NS remnants, the rotation profiles, the accretion disks, the evolution and amplification of magnetic fields, and the ejection of matter. Moreover, we discuss the connection with the central engine of SGRBs and provide order-of-magnitude estimates for the kilonova/macronova signal. Finally, we study the GW emission, with particular attention to the post-merger phase.

  13. Fission and r-process nucleosynthesis in neutron star mergers

    International Nuclear Information System (INIS)

    Giuliani, Samuel Andrea

    2018-01-01

    Fission plays a crucial role for the r-process nucleosynthesis in neutron star mergers. Due to the high neutron densities achieved in this astrophysical scenario the sequence of neutron captures and beta decays that constitutes the r process produces superheavy neutron rich nuclei that become unstable against fission. Fission determines thus the heaviest nuclei that can be produced by the r process and the fission yields shape the abundances of lighter nuclei. But despite the key role of fission the sensitivity of the r-process nucleosynthesis to uncertainties in fission predictions has not been explored. Nowadays there are only few set of fission rates suited for r-process calculations and most of them rely on a simplified treatment of the fission process. In this thesis we go beyond these approximations and compute the fission properties of r-process nuclei using the energy density functional approach. Fission is described as a tunneling process where the nucleus ''moves'' in a collective space characterized by coordinates describing the nuclear shape. Thus fission depends on the evolution of the energy with the deformation but also on the inertia due to the motion in the collective space. This is analogous to the quantum mechanical tunneling of a particle inside a potential well. In our study the relevant quantities for the description of the fission process are consistently computed for 3642 nuclei following the Hartree-Fock-Bogolyubov theory with constraining operators. We perform an extensive benchmark against the available experimental data and explore the variations of the fission properties along the superheavy landscape. We find that while collective inertias have a strong impact in the fission probabilities of light nuclei their role becomes less relevant in r -process nuclei. Within the statistical model we compute the neutron induced stellar reaction rates relevant for the r-process nucleosynthesis. These sets of stellar reaction

  14. Rapid Mergers in a Mixed System of Black Holes and Neutron Stars

    Science.gov (United States)

    Tagawa, Hiromichi; Umemura, Masayuki

    Recently, it has been argued that r-process elements in galaxies primarily originate from the mergers of double neutron stars (NSs) and black hole (BH)-NS. However, there is a momentous problem that the merger timescale is estimated to be much longer than the production timescale of r-process elements inferred from metal poor stars in the Galactic halo. To solve this problem, we propose the rapid merger processes in gas-rich first-generation objects in a high redshift epoch. In such an era, it is expected that the dynamical friction by dense gas effectively promotes the merger of compact objects. To explore the possibility of mergers in a system composed of multiple NSs as well as BHs, we perform post Newtonian N-body simulations, incorporating the gas dynamical friction, the gas accretion, and the gravitational wave emission including the recoil kick. As a result, we find that NS-NS or NS-BH can merge within 10 Myr in first-generation objects. Furthermore, to satisfy the condition of the mass ejection of r-process elements, the gas accretion rate need to be lower than 0.1 Hoyle-Lyttleton accretion rate. These results imply that the mergers in early cosmic epochs may reconcile the conflict on the timescale of NS mergers.

  15. Binary neutron star mergers: Dependence on the nuclear equation of state

    International Nuclear Information System (INIS)

    Hotokezaka, Kenta; Kyutoku, Koutarou; Okawa, Hirotada; Shibata, Masaru; Kiuchi, Kenta

    2011-01-01

    We perform a numerical-relativity simulation for the merger of binary neutron stars with 6 nuclear-theory-based equations of states (EOSs) described by piecewise polytropes. Our purpose is to explore the dependence of the dynamical behavior of the binary neutron star merger and resulting gravitational waveforms on the EOS of the supernuclear-density matter. The numerical results show that the merger process and the first outcome are classified into three types: (i) a black hole is promptly formed, (ii) a short-lived hypermassive neutron star (HMNS) is formed, (iii) a long-lived HMNS is formed. The type of the merger depends strongly on the EOS and on the total mass of the binaries. For the EOS with which the maximum mass is larger than 2M · , the lifetime of the HMNS is longer than 10 ms for a total mass m 0 =2.7M · . A recent radio observation suggests that the maximum mass of spherical neutron stars is M max ≥1.97±0.04M · in one σ level. This fact and our results support the possible existence of a HMNS soon after the onset of the merger for a typical binary neutron star with m 0 =2.7M · . We also show that the torus mass surrounding the remnant black hole is correlated with the type of the merger process; the torus mass could be large, ≥0.1M · , in the case that a long-lived HMNS is formed. We also show that gravitational waves carry information of the merger process, the remnant, and the torus mass surrounding a black hole.

  16. The incidence of stellar mergers and mass gainers among massive stars

    International Nuclear Information System (INIS)

    De Mink, S. E.; Sana, H.; Langer, N.; Izzard, R. G.; Schneider, F. R. N.

    2014-01-01

    Because the majority of massive stars are born as members of close binary systems, populations of massive main-sequence stars contain stellar mergers and products of binary mass transfer. We simulate populations of massive stars accounting for all major binary evolution effects based on the most recent binary parameter statistics and extensively evaluate the effect of model uncertainties. Assuming constant star formation, we find that 8 −4 +9 % of a sample of early-type stars are the products of a merger resulting from a close binary system. In total we find that 30 −15 +10 % of massive main-sequence stars are the products of binary interaction. We show that the commonly adopted approach to minimize the effects of binaries on an observed sample by excluding systems detected as binaries through radial velocity campaigns can be counterproductive. Systems with significant radial velocity variations are mostly pre-interaction systems. Excluding them substantially enhances the relative incidence of mergers and binary products in the non-radial velocity variable sample. This poses a challenge for testing single stellar evolutionary models. It also raises the question of whether certain peculiar classes of stars, such as magnetic O stars, are the result of binary interaction and it emphasizes the need to further study the effect of binarity on the diagnostics that are used to derive the fundamental properties (star-formation history, initial mass function, mass-to-light ratio) of stellar populations nearby and at high redshift.

  17. THE UNREASONABLE WEAKNESS OF R -PROCESS COSMIC RAYS IN THE NEUTRON-STAR-MERGER NUCLEOSYNTHESIS SCENARIO

    Energy Technology Data Exchange (ETDEWEB)

    Kyutoku, Koutarou [Interdisciplinary Theoretical Science (iTHES) Research Group, RIKEN, Wako, Saitama 351-0198 (Japan); Ioka, Kunihito, E-mail: koutarou.kyutoku@riken.jp [Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502 (Japan)

    2016-08-10

    We reach the robust conclusion that, by combining the observed cosmic rays of r -process elements with the fact that the velocity of the neutron-star-merger ejecta is much higher than that of the supernova ejecta, either (1) the reverse shock in the neutron-star-merger ejecta is a very inefficient accelerator that converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy or (2) the neutron star merger is not the origin of the Galactic r -process elements. We also find that the acceleration efficiency should be less than 0.1% for the reverse shock of the supernova ejecta with observed cosmic rays lighter than the iron.

  18. The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

    Directory of Open Access Journals (Sweden)

    Alessandro Drago

    2018-03-01

    Full Text Available We discuss the different signals, in gravitational and electromagnetic waves, emitted during the merger of two compact stars. We will focus in particular on the possible contraints that those signals can provide on the equation of state of dense matter. Indeed, the stiffness of the equation of state and the particle composition of the merging compact stars strongly affect, e.g., the life time of the post-merger remnant and its gravitational wave signal, the emission of the short gamma-ray-burst, the amount of ejected mass and the related kilonova. The first detection of gravitational waves from the merger of two compact stars in August 2017, GW170817, and the subsequent detections of its electromagnetic counterparts, GRB170817A and AT2017gfo, is the first example of the era of “multi-messenger astronomy”: we discuss what we have learned from this detection on the equation of state of compact stars and we provide a tentative interpretation of this event, within the two families scenario, as being due to the merger of a hadronic star with a quark star.

  19. Impact of star formation inhomogeneities on merger rates and interpretation of LIGO results

    International Nuclear Information System (INIS)

    O'Shaughnessy, R; Kopparapu, R K; Belczynski, K

    2012-01-01

    Within the next decade, ground based gravitational-wave detectors are in principle capable of determining the compact object merger rate per unit volume of the local universe to better than 20% with more than 30 detections. These measurements will constrain our models of stellar, binary and star cluster evolution in the nearby present-day and ancient universe. We argue that the stellar models are sensitive to heterogeneities (in age and metallicity at least) in such a way that the predicted merger rates are subject to an additional 30-50% systematic errors unless these heterogeneities are taken into account. Without adding new electromagnetic constraints on massive binary evolution or relying on more information from each merger (e.g., binary masses and spins), as few as the 5 merger detections could exhaust the information available in a naive comparison to merger rate predictions. As a concrete example immediately relevant to analysis of initial and enhanced LIGO results, we use a nearby-universe catalog to demonstrate that no one tracer of stellar content can be consistently used to constrain merger rates without introducing a systematic error of order O(30%) at 90% confidence (depending on the type of binary involved). For example, though binary black holes typically take many Gyr to merge, binary neutron stars often merge rapidly; different tracers of stellar content are required for these two types. More generally, we argue that theoretical binary evolution can depend sufficiently sensitively on star-forming conditions-even assuming no uncertainty in binary evolution model-that the distribution of star-forming conditions must be incorporated to reduce the systematic error in merger rate predictions below roughly 40%. We emphasize that the degree of sensitivity to star-forming conditions depends on the binary evolution model and on the amount of relevant variation in star-forming conditions. For example, if after further comparison with electromagnetic and

  20. REPRODUCING THE OBSERVED ABUNDANCES IN RCB AND HdC STARS WITH POST-DOUBLE-DEGENERATE MERGER MODELS-CONSTRAINTS ON MERGER AND POST-MERGER SIMULATIONS AND PHYSICS PROCESSES

    Energy Technology Data Exchange (ETDEWEB)

    Menon, Athira; Herwig, Falk; Denissenkov, Pavel A. [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada); Clayton, Geoffrey C.; Staff, Jan [Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Tower Dr., Baton Rouge, LA 70803-4001 (United States); Pignatari, Marco [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland); Paxton, Bill [Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)

    2013-07-20

    The R Coronae Borealis (RCB) stars are hydrogen-deficient, variable stars that are most likely the result of He-CO WD mergers. They display extremely low oxygen isotopic ratios, {sup 16}O/{sup 18}O {approx_equal} 1-10, {sup 12}C/{sup 13}C {>=} 100, and enhancements up to 2.6 dex in F and in s-process elements from Zn to La, compared to solar. These abundances provide stringent constraints on the physical processes during and after the double-degenerate merger. As shown previously, O-isotopic ratios observed in RCB stars cannot result from the dynamic double-degenerate merger phase, and we now investigate the role of the long-term one-dimensional spherical post-merger evolution and nucleosynthesis based on realistic hydrodynamic merger progenitor models. We adopt a model for extra envelope mixing to represent processes driven by rotation originating in the dynamical merger. Comprehensive nucleosynthesis post-processing simulations for these stellar evolution models reproduce, for the first time, the full range of the observed abundances for almost all the elements measured in RCB stars: {sup 16}O/{sup 18}O ratios between 9 and 15, C-isotopic ratios above 100, and {approx}1.4-2.35 dex F enhancements, along with enrichments in s-process elements. The nucleosynthesis processes in our models constrain the length and temperature in the dynamic merger shell-of-fire feature as well as the envelope mixing in the post-merger phase. s-process elements originate either in the shell-of-fire merger feature or during the post-merger evolution, but the contribution from the asymptotic giant branch progenitors is negligible. The post-merger envelope mixing must eventually cease {approx}10{sup 6} yr after the dynamic merger phase before the star enters the RCB phase.

  1. REPRODUCING THE OBSERVED ABUNDANCES IN RCB AND HdC STARS WITH POST-DOUBLE-DEGENERATE MERGER MODELS—CONSTRAINTS ON MERGER AND POST-MERGER SIMULATIONS AND PHYSICS PROCESSES

    International Nuclear Information System (INIS)

    Menon, Athira; Herwig, Falk; Denissenkov, Pavel A.; Clayton, Geoffrey C.; Staff, Jan; Pignatari, Marco; Paxton, Bill

    2013-01-01

    The R Coronae Borealis (RCB) stars are hydrogen-deficient, variable stars that are most likely the result of He-CO WD mergers. They display extremely low oxygen isotopic ratios, 16 O/ 18 O ≅ 1-10, 12 C/ 13 C ≥ 100, and enhancements up to 2.6 dex in F and in s-process elements from Zn to La, compared to solar. These abundances provide stringent constraints on the physical processes during and after the double-degenerate merger. As shown previously, O-isotopic ratios observed in RCB stars cannot result from the dynamic double-degenerate merger phase, and we now investigate the role of the long-term one-dimensional spherical post-merger evolution and nucleosynthesis based on realistic hydrodynamic merger progenitor models. We adopt a model for extra envelope mixing to represent processes driven by rotation originating in the dynamical merger. Comprehensive nucleosynthesis post-processing simulations for these stellar evolution models reproduce, for the first time, the full range of the observed abundances for almost all the elements measured in RCB stars: 16 O/ 18 O ratios between 9 and 15, C-isotopic ratios above 100, and ∼1.4-2.35 dex F enhancements, along with enrichments in s-process elements. The nucleosynthesis processes in our models constrain the length and temperature in the dynamic merger shell-of-fire feature as well as the envelope mixing in the post-merger phase. s-process elements originate either in the shell-of-fire merger feature or during the post-merger evolution, but the contribution from the asymptotic giant branch progenitors is negligible. The post-merger envelope mixing must eventually cease ∼10 6 yr after the dynamic merger phase before the star enters the RCB phase

  2. Repeating and non-repeating fast radio bursts from binary neutron star mergers

    Science.gov (United States)

    Yamasaki, Shotaro; Totani, Tomonori; Kiuchi, Kenta

    2018-04-01

    Most fast radio bursts (FRB) do not show evidence of repetition, and such non-repeating FRBs may be produced at the time of a merger of binary neutron stars (BNS), provided that the BNS merger rate is close to the high end of the currently possible range. However, the merger environment is polluted by dynamical ejecta, which may prohibit the radio signal from propagating. We examine this by using a general-relativistic simulation of a BNS merger, and show that the ejecta appears about 1 ms after the rotation speed of the merged star becomes the maximum. Therefore there is a time window in which an FRB signal can reach outside, and the short duration of non-repeating FRBs can be explained by screening after ejecta formation. A fraction of BNS mergers may leave a rapidly rotating and stable neutron star, and such objects may be the origin of repeating FRBs like FRB 121102. We show that a merger remnant would appear as a repeating FRB on a time scale of ˜1-10 yr, and expected properties are consistent with the observations of FRB 121102. We construct an FRB rate evolution model that includes these two populations of repeating and non-repeating FRBs from BNS mergers, and show that the detection rate of repeating FRBs relative to non-repeating ones rapidly increases with improving search sensitivity. This may explain why only the repeating FRB 121102 was discovered by the most sensitive FRB search with Arecibo. Several predictions are made, including the appearance of a repeating FRB 1-10 yr after a BNS merger that is localized by gravitational waves and subsequent electromagnetic radiation.

  3. BRIGHT 'MERGER-NOVA' FROM THE REMNANT OF A NEUTRON STAR BINARY MERGER: A SIGNATURE OF A NEWLY BORN, MASSIVE, MILLISECOND MAGNETAR

    International Nuclear Information System (INIS)

    Yu, Yun-Wei; Zhang, Bing; Gao, He

    2013-01-01

    A massive millisecond magnetar may survive the merger of a neutron star (NS) binary, which would continuously power the merger ejecta. We develop a generic dynamic model for the merger ejecta with energy injection from the central magnetar. The ejecta emission (the m erger-nova ) powered by the magnetar peaks in the UV band and the peak of the light curve, progressively shifts to an earlier epoch with increasing frequency. A magnetar-powered merger-nova could have an optical peak brightness comparable to a supernova, which is a few tens or hundreds times brighter than the radioactive-powered merger-novae (the so-called macro-nova or kilo-nova). On the other hand, such a merger-nova would peak earlier and have a significantly shorter duration than that of a supernova. An early collapse of the magnetar could suppress the brightness of the optical emission and shorten its duration. Such millisecond-magnetar-powered merger-novae may be detected from NS-NS merger events without an observed short gamma-ray burst, and could be a bright electromagnetic counterpart for gravitational wave bursts due to NS-NS mergers. If detected, it suggests that the merger leaves behind a massive NS, which has important implications for the equation-of-state of nuclear matter

  4. GW170817: a neutron star merger in a mass-transferring triple system

    Science.gov (United States)

    Chang, Philip; Murray, Norman

    2018-02-01

    The light curve of GW170817 is surprisingly blue and bright. Assuming that the event is a binary neutron star merger, we argue that blueness and brightness of the light curve is the result of ejecta that contains an substantial amount of thermal energy. To achieve this, the ejecta must be reheated at a substantial distance (1-2000 solar radii) from the merger to avoid losing the energy to adiabatic cooling. We show that this reheating can occur if the merger occurs in a hierarchical triple system where the outer star has evolved and filled its Roche lobe. The outer star feeds mass to the inner binary, forming a circumbinary disc, driving the inner binary to merge. Because the outer star fills its Roche lobe, a substantial fraction of the dynamical ejecta collides with the evolved star, reheating the ejecta in the process. We suggest that the process of mass transfer in hierarchical triples tends to form coplanar triple systems such as PSR J0337+1715, and may provide electromagnetic counterparts to binary black hole mergers.

  5. Reconciling mass functions with the star-forming main sequence via mergers

    Science.gov (United States)

    Steinhardt, Charles L.; Yurk, Dominic; Capak, Peter

    2017-06-01

    We combine star formation along the 'main sequence', quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.

  6. The role of neutron star mergers in the chemical evolution of the Galactic halo

    Science.gov (United States)

    Cescutti, G.; Romano, D.; Matteucci, F.; Chiappini, C.; Hirschi, R.

    2015-05-01

    Context. The dominant astrophysical production site of the r-process elements has not yet been unambiguously identified. The suggested main r-process sites are core-collapse supernovae and merging neutron stars. Aims: We explore the problem of the production site of Eu. We also use the information present in the observed spread in the Eu abundances in the early Galaxy, and not only its average trend. Moreover, we extend our investigations to other heavy elements (Ba, Sr, Rb, Zr) to provide additional constraints on our results. Methods: We adopt a stochastic chemical evolution model that takes inhomogeneous mixing into account. The adopted yields of Eu from merging neutron stars and from core-collapse supernovae are those that are able to explain the average [Eu/Fe]-[Fe/H] trend observed for solar neighbourhood stars, the solar abundance of Eu, and the present-day abundance gradient of Eu along the Galactic disc in the framework of a well-tested homogeneous model for the chemical evolution of the Milky Way. Rb, Sr, Zr, and Ba are produced by both the s- and r-processes. The r-process yields were obtained by scaling the Eu yields described above according to the abundance ratios observed in r-process rich stars. The s-process contribution by spinstars is the same as in our previous papers. Results: Neutron star binaries that merge in less than 10 Myr or neutron star mergers combined with a source of r-process generated by massive stars can explain the spread of [Eu/Fe] in the Galactic halo. The combination of r-process production by neutron star mergers and s-process production by spinstars is able to reproduce the available observational data for Sr, Zr, and Ba. We also show the first predictions for Rb in the Galactic halo. Conclusions: We confirm previous results that either neutron star mergers on a very short timescale or both neutron star mergers and at least a fraction of Type II supernovae have contributed to the synthesis of Eu in the Galaxy. The r

  7. The spatial extent and distribution of star formation in 3D-HST mergers at z ˜ 1.5

    Science.gov (United States)

    Schmidt, Kasper B.; Rix, Hans-Walter; da Cunha, Elisabete; Brammer, Gabriel B.; Cox, Thomas J.; van Dokkum, Pieter; Förster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Jonsson, Patrik; Lundgren, Britt; Maseda, Michael V.; Momcheva, Ivelina; Nelson, Erica J.; Skelton, Rosalind E.; van der Wel, Arjen; Whitaker, Katherine E.

    2013-06-01

    We present an analysis of the spatial distribution of star formation in a sample of 60 visually identified galaxy merger candidates at z > 1. Our sample, drawn from the 3D-HST survey, is flux limited and was selected to have high star formation rates based on fits of their broad-band, low spatial resolution spectral energy distributions. It includes plausible pre-merger (close pairs) and post-merger (single objects with tidal features) systems, with total stellar masses and star formation rates derived from multiwavelength photometry. Here we use near-infrared slitless spectra from 3D-HST which produce Hα or [O III] emission line maps as proxies for star formation maps. This provides a first comprehensive high-resolution, empirical picture of where star formation occurred in galaxy mergers at the epoch of peak cosmic star formation rate. We find that detectable star formation can occur in one or both galaxy centres, or in tidal tails. The most common case (58 per cent) is that star formation is largely concentrated in a single, compact region, coincident with the centre of (one of) the merger components. No correlations between star formation morphology and redshift, total stellar mass or star formation rate are found. A restricted set of hydrodynamical merger simulations between similarly massive and gas-rich objects implies that star formation should be detectable in both merger components, when the gas fractions of the individual components are the same. This suggests that z ˜ 1.5 mergers typically occur between galaxies whose gas fractions, masses and/or star formation rates are distinctly different from one another.

  8. Search for Post-merger Gravitational Waves from the Remnant of the Binary Neutron Star Merger GW170817

    Science.gov (United States)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Afrough, M.; Agarwal, B.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allen, G.; Allocca, A.; Altin, P. A.; Amato, A.; Ananyeva, A.; Anderson, S. B.; Anderson, W. G.; Angelova, S. V.; Antier, S.; Appert, S.; Arai, K.; Araya, M. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Atallah, D. V.; Aufmuth, P.; Aulbert, C.; AultONeal, K.; Austin, C.; Avila-Alvarez, A.; Babak, S.; Bacon, P.; Bader, M. K. M.; Bae, S.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Banagiri, S.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barkett, K.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Bawaj, M.; Bayley, J. C.; Bazzan, M.; Bécsy, B.; Beer, C.; Bejger, M.; Belahcene, I.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Bernuzzi, S.; Bero, J. J.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Billman, C. R.; Birch, J.; Birney, R.; Birnholtz, O.; Biscans, S.; Biscoveanu, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blackman, J.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bode, N.; Boer, M.; Bogaert, G.; Bohe, A.; Bondu, F.; Bonilla, E.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bossie, K.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T. A.; Calloni, E.; Camp, J. B.; Canepa, M.; Canizares, P.; Cannon, K. C.; Cao, H.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Carney, M. F.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerdá-Durán, P.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chase, E.; Chassande-Mottin, E.; Chatterjee, D.; Cheeseboro, B. D.; Chen, H. Y.; Chen, X.; Chen, Y.; Cheng, H.-P.; Chia, H.; Chincarini, A.; Chiummo, A.; Chmiel, T.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, A. J. K.; Chua, S.; Chung, A. K. W.; Chung, S.; Ciani, G.; Ciolfi, R.; Cirelli, C. E.; Cirone, A.; Clara, F.; Clark, J. A.; Clearwater, P.; Cleva, F.; Cocchieri, C.; Coccia, E.; Cohadon, P.-F.; Cohen, D.; Colla, A.; Collette, C. G.; Cominsky, L. R.; Constancio, M., Jr.; Conti, L.; Cooper, S. J.; Corban, P.; Corbitt, T. R.; Cordero-Carrión, I.; Corley, K. R.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Covas, P. B.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Creighton, J. D. E.; Creighton, T. D.; Cripe, J.; Crowder, S. G.; Cullen, T. J.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Dálya, G.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davis, D.; Daw, E. J.; Day, B.; De, S.; DeBra, D.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Demos, N.; Denker, T.; Dent, T.; De Pietri, R.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; De Rossi, C.; DeSalvo, R.; de Varona, O.; Devenson, J.; Dhurandhar, S.; Díaz, M. C.; Dietrich, T.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Renzo, F.; Doctor, Z.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Dorrington, I.; Douglas, R.; Dovale Álvarez, M.; Downes, T. P.; Drago, M.; Dreissigacker, C.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dupej, P.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Eisenstein, R. A.; Essick, R. C.; Estevez, D.; Etienne, Z. B.; Etzel, T.; Evans, M.; Evans, T. M.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Farinon, S.; Farr, B.; Farr, W. M.; Fauchon-Jones, E. J.; Favata, M.; Fays, M.; Fee, C.; Fehrmann, H.; Feicht, J.; Fejer, M. M.; Fernandez-Galiana, A.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Finstad, D.; Fiori, I.; Fiorucci, D.; Fishbach, M.; Fisher, R. P.; Fitz-Axen, M.; Flaminio, R.; Fletcher, M.; Flynn, E.; Fong, H.; Font, J. A.; Forsyth, P. W. F.; Forsyth, S. S.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fries, E. M.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H.; Gadre, B. U.; Gaebel, S. M.; Gair, J. R.; Gammaitoni, L.; Ganija, M. R.; Gaonkar, S. G.; Garcia-Quiros, C.; Garufi, F.; Gateley, B.; Gaudio, S.; Gaur, G.; Gayathri, V.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; George, D.; George, J.; Gergely, L.; Germain, V.; Ghonge, S.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glover, L.; Goetz, E.; Goetz, R.; Gomes, S.; Goncharov, B.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Gretarsson, E. M.; Groot, P.; Grote, H.; Grunewald, S.; Gruning, P.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Halim, O.; Hall, B. R.; Hall, E. D.; Hamilton, E. Z.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hannuksela, O. A.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Haster, C.-J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hinderer, T.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Horst, C.; Hough, J.; Houston, E. A.; Howell, E. J.; Hreibi, A.; Hu, Y. M.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Inta, R.; Intini, G.; Isa, H. N.; Isac, J.-M.; Isi, M.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Junker, J.; Kalaghatgi, C. V.; Kalogera, V.; Kamai, B.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Kastaun, W.; Katolik, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kawabe, K.; Kéfélian, F.; Keitel, D.; Kemball, A. J.; Kennedy, R.; Kent, C.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J. C.; Kim, K.; Kim, W.; Kim, W. S.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kinley-Hanlon, M.; Kirchhoff, R.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Knowles, T. D.; Koch, P.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Krämer, C.; Kringel, V.; Krishnan, B.; Królak, A.; Kuehn, G.; Kumar, P.; Kumar, R.; Kumar, S.; Kuo, L.; Kutynia, A.; Kwang, S.; Lackey, B. D.; Lai, K. H.; Landry, M.; Lang, R. N.; Lange, J.; Lantz, B.; Lanza, R. K.; Lartaux-Vollard, A.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, H. W.; Lee, K.; Lehmann, J.; Lenon, A.; Leonardi, M.; Leroy, N.; Letendre, N.; Levin, Y.; Li, T. G. F.; Linker, S. D.; Liu, J.; Lo, R. K. L.; Lockerbie, N. A.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lousto, C. O.; Lovelace, G.; Lück, H.; Lumaca, D.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macas, R.; Macfoy, S.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña Hernandez, I.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markakis, C.; Markosyan, A. S.; Markowitz, A.; Maros, E.; Marquina, A.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Mason, K.; Massera, E.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matas, A.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McCuller, L.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McNeill, L.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Mejuto-Villa, E.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, B. B.; Miller, J.; Milovich-Goff, M. C.; Minazzoli, O.; Minenkov, Y.; Ming, J.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moffa, D.; Moggi, A.; Mogushi, K.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Muñiz, E. A.; Muratore, M.; Murray, P. G.; Napier, K.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Neilson, J.; Nelemans, G.; Nelson, T. J. N.; Nery, M.; Neunzert, A.; Nevin, L.; Newport, J. M.; Newton, G.; Ng, K. K. Y.; Nguyen, T. T.; Nichols, D.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Noack, A.; Nocera, F.; Nolting, D.; North, C.; Nuttall, L. K.; Oberling, J.; O'Dea, G. D.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Okada, M. A.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; Ormiston, R.; Ortega, L. F.; O'Shaughnessy, R.; Ossokine, S.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pace, A. E.; Page, J.; Page, M. A.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, Howard; Pan, Huang-Wei; Pang, B.; Pang, P. T. H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Parida, A.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patil, M.; Patricelli, B.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perez, C. J.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Phukon, K. S.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pirello, M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Porter, E. K.; Post, A.; Powell, J.; Prasad, J.; Pratt, J. W. W.; Pratten, G.; Predoi, V.; Prestegard, T.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L. G.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rajbhandari, B.; Rakhmanov, M.; Ramirez, K. E.; Ramos-Buades, A.; Rapagnani, P.; Raymond, V.; Razzano, M.; Read, J.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Ren, W.; Reyes, S. D.; Ricci, F.; Ricker, P. M.; Rieger, S.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romel, C. L.; Romie, J. H.; Rosińska, D.; Ross, M. P.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Rutins, G.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sampson, L. M.; Sanchez, E. J.; Sanchez, L. E.; Sanchis-Gual, N.; Sandberg, V.; Sanders, J. R.; Sarin, N.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Scheel, M.; Scheuer, J.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schulte, B. W.; Schutz, B. F.; Schwalbe, S. G.; Scott, J.; Scott, S. M.; Seidel, E.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Shaddock, D. A.; Shaffer, T. J.; Shah, A. A.; Shahriar, M. S.; Shaner, M. B.; Shao, L.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, L. P.; Singh, A.; Singhal, A.; Sintes, A. M.; Rana, J.; Slagmolen, B. J. J.; Smith, B.; Smith, J. R.; Smith, R. J. E.; Somala, S.; Son, E. J.; Sonnenberg, J. A.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Sowell, E.; Spencer, A. P.; Srivastava, A. K.; Staats, K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stevenson, S. P.; Stone, R.; Stops, D. J.; Strain, K. A.; Stratta, G.; Strigin, S. E.; Strunk, A.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Suresh, J.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Tait, S. C.; Talbot, C.; Talukder, D.; Tanner, D. B.; Tápai, M.; Taracchini, A.; Tasson, J. D.; Taylor, J. A.; Taylor, R.; Tewari, S. V.; Theeg, T.; Thies, F.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tonelli, M.; Tornasi, Z.; Torres-Forné, A.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trinastic, J.; Tringali, M. C.; Trozzo, L.; Tsang, K. W.; Tse, M.; Tso, R.; Tsukada, L.; Tsuna, D.; Tuyenbayev, D.; Ueno, K.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Varma, V.; Vass, S.; Vasúth, M.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Venugopalan, G.; Verkindt, D.; Vetrano, F.; Viceré, A.; Viets, A. D.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walet, R.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, J. Z.; Wang, W. H.; Wang, Y. F.; Ward, R. L.; Warner, J.; Was, M.; Watchi, J.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wessel, E. K.; Weßels, P.; Westerweck, J.; Westphal, T.; Wette, K.; Whelan, J. T.; White, D. D.; Whiting, B. F.; Whittle, C.; Wilken, D.; Williams, D.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Wofford, J.; Wong, K. W. K.; Worden, J.; Wright, J. L.; Wu, D. S.; Wysocki, D. M.; Xiao, S.; Yamamoto, H.; Yancey, C. C.; Yang, L.; Yap, M. J.; Yazback, M.; Yu, Hang; Yu, Haocun; Yvert, M.; Zadrożny, A.; Zanolin, M.; Zelenova, T.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, T.; Zhang, Y.-H.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, S. J.; Zhu, X. J.; Zimmerman, A. B.; Zucker, M. E.; Zweizig, J.; (LIGO Scientific Collaboration; Virgo Collaboration

    2017-12-01

    The first observation of a binary neutron star (NS) coalescence by the Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors offers an unprecedented opportunity to study matter under the most extreme conditions. After such a merger, a compact remnant is left over whose nature depends primarily on the masses of the inspiraling objects and on the equation of state of nuclear matter. This could be either a black hole (BH) or an NS, with the latter being either long-lived or too massive for stability implying delayed collapse to a BH. Here, we present a search for GWs from the remnant of the binary NS merger GW170817 using data from Advanced LIGO and Advanced Virgo. We search for short- (≲1 s) and intermediate-duration (≲500 s) signals, which include GW emission from a hypermassive NS or supramassive NS, respectively. We find no signal from the post-merger remnant. Our derived strain upper limits are more than an order of magnitude larger than those predicted by most models. For short signals, our best upper limit on the root sum square of the GW strain emitted from 1-4 kHz is {h}{rss}50 % =2.1× {10}-22 {{Hz}}-1/2 at 50% detection efficiency. For intermediate-duration signals, our best upper limit at 50% detection efficiency is {h}{rss}50 % =8.4× {10}-22 {{Hz}}-1/2 for a millisecond magnetar model, and {h}{rss}50 % =5.9× {10}-22 {{Hz}}-1/2 for a bar-mode model. These results indicate that post-merger emission from a similar event may be detectable when advanced detectors reach design sensitivity or with next-generation detectors.

  9. DO R CORONAE BOREALIS STARS FORM FROM DOUBLE WHITE DWARF MERGERS?

    Energy Technology Data Exchange (ETDEWEB)

    Staff, Jan. E.; Clayton, Geoffrey C.; Tohline, Joel E. [Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Tower Drive, Baton Rouge, LA 70803-4001 (United States); Menon, Athira; Herwig, Falk [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada); Even, Wesley; Fryer, Chris L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Motl, Patrick M. [Department of Science, Mathematics and Informatics, Indiana University Kokomo, Kokomo, IN 46904-9003 (United States); Geballe, Tom [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Pignatari, Marco [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)

    2012-09-20

    A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WDs) in a binary. The observed ratio of {sup 16}O/{sup 18}O for RCB stars is in the range of 0.3-20 much smaller than the solar value of {approx}500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He WD. We present the results of five three-dimensional hydrodynamic simulations of the merger of a double WD system where the total mass is 0.9 M{sub Sun} and the initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations with q {approx}< 0.7 a feature around the merged stars where the temperatures and densities are suitable for forming {sup 18}O. However, more {sup 16}O is being dredged up from the C- and O-rich accretor during the merger than the amount of {sup 18}O that is produced. Therefore, on the dynamical timescale over which our hydrodynamics simulation runs, an {sup 16}O/{sup 18}O ratio of {approx}2000 in the 'best' case is found. If the conditions found in the hydrodynamic simulations persist for 10{sup 6} s the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to {approx}4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two WDs remains a strong candidate for the formation of these enigmatic stars.

  10. TIDAL TAILS OF MINOR MERGERS: STAR FORMATION EFFICIENCY IN THE WESTERN TAIL OF NGC 2782

    Energy Technology Data Exchange (ETDEWEB)

    Knierman, Karen; Scowen, Paul; Jansen, Rolf A. [School of Earth and Space Exploration, Arizona State University, 550 East Tyler Mall, Room PSF-686 (P.O. Box 871404), Tempe, AZ 85287-1404 (United States); Knezek, Patricia M. [WIYN Consortium, Inc., 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Wehner, Elizabeth, E-mail: karen.knierman@asu.edu, E-mail: paul.scowen@asu.edu, E-mail: rolf.jansen@asu.edu, E-mail: pknezek@noao.edu, E-mail: ewehner@haverford.edu [Department of Astronomy, Haverford College, Haverford, PA 19041 (United States)

    2012-04-10

    While major mergers and their tidal debris are well studied, they are less common than minor mergers (mass ratios {approx}< 0.3). The peculiar spiral NGC 2782 is the result of a merger between two disk galaxies with a mass ratio of {approx}4: 1 occurring {approx}200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun to occur in that tidal tail. However, deep H{alpha} narrowband images show evidence of recent star formation in the western tail. Across the entire western tail, we find the global star formation rate per unit area ({Sigma}{sub SFR}) to be several orders of magnitude less than expected from the total gas density. Together with extended FUV+NUV emission from Galaxy Evolution Explorer along the tail, this indicates a low global star formation efficiency in the tidal tail producing lower mass star clusters. The H II region that we observed has a local (few-kiloparsec scale) {Sigma}{sub SFR} from H{alpha} that is less than that expected from the total gas density, which is consistent with other observations of tidal debris. The star formation efficiency of this H II region inferred from the total gas density is low, but normal when inferred from the molecular gas density. These results suggest the presence of a very small, locally dense region in the western tail of NGC 2782 or of a low-metallicity and/or low-pressure star-forming region.

  11. Viscous Dissipation and Heat Conduction in Binary Neutron-Star Mergers

    Science.gov (United States)

    Alford, Mark G.; Bovard, Luke; Hanauske, Matthias; Rezzolla, Luciano; Schwenzer, Kai

    2018-01-01

    Inferring the properties of dense matter is one of the most exciting prospects from the measurement of gravitational waves from neutron star mergers. However, it requires reliable numerical simulations that incorporate viscous dissipation and energy transport as these can play a significant role in the survival time of the post-merger object. We calculate time scales for typical forms of dissipation and find that thermal transport and shear viscosity will not be important unless neutrino trapping occurs, which requires temperatures above 10 MeV and gradients over length scales of 0.1 km or less. On the other hand, if direct-Urca processes remain suppressed, leaving modified-Urca processes to establish flavor equilibrium, then bulk viscous dissipation could provide significant damping to density oscillations right after merger. When comparing with data from state-of-the-art merger simulations, we find that the bulk viscosity takes values close to its resonant maximum in a typical merger, motivating a more careful assessment of the role of bulk viscous dissipation in the gravitational-wave signal from merging neutron stars.

  12. Viscous Dissipation and Heat Conduction in Binary Neutron-Star Mergers.

    Science.gov (United States)

    Alford, Mark G; Bovard, Luke; Hanauske, Matthias; Rezzolla, Luciano; Schwenzer, Kai

    2018-01-26

    Inferring the properties of dense matter is one of the most exciting prospects from the measurement of gravitational waves from neutron star mergers. However, it requires reliable numerical simulations that incorporate viscous dissipation and energy transport as these can play a significant role in the survival time of the post-merger object. We calculate time scales for typical forms of dissipation and find that thermal transport and shear viscosity will not be important unless neutrino trapping occurs, which requires temperatures above 10 MeV and gradients over length scales of 0.1 km or less. On the other hand, if direct-Urca processes remain suppressed, leaving modified-Urca processes to establish flavor equilibrium, then bulk viscous dissipation could provide significant damping to density oscillations right after merger. When comparing with data from state-of-the-art merger simulations, we find that the bulk viscosity takes values close to its resonant maximum in a typical merger, motivating a more careful assessment of the role of bulk viscous dissipation in the gravitational-wave signal from merging neutron stars.

  13. ELECTROMAGNETIC EMISSION FROM LONG-LIVED BINARY NEUTRON STAR MERGER REMNANTS. II. LIGHT CURVES AND SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, Daniel M. [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, D-14476 Potsdam-Golm (Germany); Ciolfi, Riccardo, E-mail: daniel.siegel@aei.mpg.de, E-mail: riccardo.ciolfi@unitn.it [Physics Department, University of Trento, Via Sommarive 14, I-38123 Trento (Italy)

    2016-03-01

    Recent observations indicate that in a large fraction of binary neutron star (BNS) mergers a long-lived neutron star (NS) may be formed rather than a black hole. Unambiguous electromagnetic (EM) signatures of such a scenario would strongly impact our knowledge on how short gamma-ray bursts (SGRBs) and their afterglow radiation are generated. Furthermore, such EM signals would have profound implications for multimessenger astronomy with joint EM and gravitational-wave (GW) observations of BNS mergers, which will soon become reality thanks to the ground-based advanced LIGO/Virgo GW detector network. Here we explore such EM signatures based on the model presented in a companion paper, which provides a self-consistent evolution of the post-merger system and its EM emission up to ∼10{sup 7} s. Light curves and spectra are computed for a wide range of post-merger physical properties. We present X-ray afterglow light curves corresponding to the “standard” and the “time-reversal” scenario for SGRBs (prompt emission associated with the merger or with the collapse of the long-lived NS). The light curve morphologies include single and two-plateau features with timescales and luminosities that are in good agreement with Swift observations. Furthermore, we compute the X-ray signal that should precede the SGRB in the time-reversal scenario, the detection of which would represent smoking-gun evidence for this scenario. Finally, we find a bright, highly isotropic EM transient peaking in the X-ray band at ∼10{sup 2}–10{sup 4} s after the BNS merger with luminosities of L{sub X} ∼ 10{sup 46}–10{sup 48} erg s{sup −1}. This signal represents a very promising EM counterpart to the GW emission from BNS mergers.

  14. Detectability of thermal neutrinos from binary neutron-star mergers and implications for neutrino physics

    Science.gov (United States)

    Kyutoku, Koutarou; Kashiyama, Kazumi

    2018-05-01

    We propose a long-term strategy for detecting thermal neutrinos from the remnant of binary neutron-star mergers with a future M-ton water-Cherenkov detector such as Hyper-Kamiokande. Monitoring ≳2500 mergers within ≲200 Mpc , we may be able to detect a single neutrino with a human time-scale operation of ≈80 Mtyears for the merger rate of 1 Mpc-3 Myr-1 , which is slightly lower than the median value derived by the LIGO-Virgo Collaboration with GW170817. Although the number of neutrino events is minimal, contamination from other sources of neutrinos can be reduced efficiently to ≈0.03 by analyzing only ≈1 s after each merger identified with gravitational-wave detectors if gadolinium is dissolved in the water. The contamination may be reduced further to ≈0.01 if we allow the increase of waiting time by a factor of ≈1.7 . The detection of even a single neutrino can pin down the energy scale of thermal neutrino emission from binary neutron-star mergers and could strongly support or disfavor formation of remnant massive neutron stars. Because the dispersion relation of gravitational waves is now securely constrained to that of massless particles with a corresponding limit on the graviton mass of ≲10-22 eV /c2 by binary black-hole mergers, the time delay of a neutrino from gravitational waves can be used to put an upper limit of ≲O (10 ) meV /c2 on the absolute neutrino mass in the lightest eigenstate. Large neutrino detectors will enhance the detectability, and, in particular, 5 Mt Deep-TITAND and 10 Mt MICA planned in the future will allow us to detect thermal neutrinos every ≈16 and 8 years, respectively, increasing the significance.

  15. The cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers

    Science.gov (United States)

    Gottlieb, Ore; Nakar, Ehud; Piran, Tsvi

    2018-01-01

    Short gamma-ray bursts are believed to arise from compact binary mergers (either neutron star-neutron star or black hole-neutron star). If so, their jets must penetrate outflows that are ejected during the merger. As a jet crosses the ejecta, it dissipates its energy, producing a hot cocoon that surrounds it. We present here 3D numerical simulations of jet propagation in mergers' outflows, and we calculate the resulting emission. This emission consists of two components: the cooling emission, the leakage of the thermal energy of the hot cocoon, and the cocoon macronova that arises from the radioactive decay of the cocoon's material. This emission gives a brief (∼1 h) blue, wide angle signal. While the parameters of the outflow and jet are uncertain, for the configurations we have considered, the signal is bright (∼-14 to -15 absolute magnitude) and outshines all other predicted ultraviolet-optical signals. The signal is brighter when the jet breakout time is longer, and its peak brightness does not depend strongly on the highly uncertain opacity. A rapid search for such a signal is a promising strategy to detect an electromagnetic merger counterpart. A detected candidate could be then followed by deep infrared searches for the longer but weaker macronova arising from the rest of the ejecta.

  16. The Properties of Short Gamma-Ray Burst Jets Triggered by Neutron Star Mergers

    Energy Technology Data Exchange (ETDEWEB)

    Murguia-Berthier, Ariadna; Ramirez-Ruiz, Enrico; Montes, Gabriela [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); De Colle, Fabio [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A. P. 70-543 04510 D. F. (Mexico); Rezzolla, Luciano; Takami, Kentaro [Institute for Theoretical Physics, Goethe University, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main (Germany); Rosswog, Stephan [Astronomy and Oskar Klein Centre, Stockholm University, AlbaNova, SE-106 91 Stockholm (Sweden); Perego, Albino [Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt (Germany); Lee, William H. [Instituto de Astronomía, Universidad Nacional Autónoma de México, A. P. 70-264 04510 D. F. (Mexico)

    2017-02-01

    The most popular model for short gamma-ray bursts (sGRBs) involves the coalescence of binary neutron stars. Because the progenitor is actually hidden from view, we must consider under which circumstances such merging systems are capable of producing a successful sGRB. Soon after coalescence, winds are launched from the merger remnant. In this paper, we use realistic wind profiles derived from global merger simulations in order to investigate the interaction of sGRB jets with these winds using numerical simulations. We analyze the conditions for which these axisymmetric winds permit relativistic jets to break out and produce an sGRB. We find that jets with luminosities comparable to those observed in sGRBs are only successful when their half-opening angles are below ≈20°. This jet collimation mechanism leads to a simple physical interpretation of the luminosities and opening angles inferred for sGRBs. If wide, low-luminosity jets are observed, they might be indicative of a different progenitor avenue such as the merger of a neutron star with a black hole. We also use the observed durations of sGRB to place constraints on the lifetime of the wind phase, which is determined by the time it takes the jet to break out. In all cases we find that the derived limits argue against completely stable remnants for binary neutron star mergers that produce sGRBs.

  17. Star formation history of the galaxy merger Mrk848 with SDSS-IV MaNGA

    Science.gov (United States)

    Yuan, Fang-Ting; Shen, Shiyin; Hao, Lei; Fernandez, Maria Argudo

    2017-03-01

    With the 3D data of SDSS-IV MaNGA (Bundy et al. 2015) spectra and multi-wavelength SED modeling, we expect to have a better understanding of the distribution of dust, gas and star formation of galaxy mergers. For a case study of the merging galaxy Mrk848, we use both UV-to-IR broadband SED and the MaNGA integral field spectroscopy to obtain its star formation histories at the tail and core regions. From the SED fitting and full spectral fitting, we find that the star formation in the tail regions are affected by the interaction earlier than the core regions. The core regions show apparently two times of star formation and a strong burst within 500Myr, indicating the recent star formation is triggered by the interaction. The star formation histories derived from these two methods are basically consistent.

  18. MODELS OF KILONOVA/MACRONOVA EMISSION FROM BLACK HOLE–NEUTRON STAR MERGERS

    International Nuclear Information System (INIS)

    Kawaguchi, Kyohei; Shibata, Masaru; Kyutoku, Koutarou; Tanaka, Masaomi

    2016-01-01

    Black hole–neutron star (BH–NS) mergers are among the most promising gravitational-wave sources for ground-based detectors, and gravitational waves from BH–NS mergers are expected to be detected in the next few years. The simultaneous detection of electromagnetic counterparts with gravitational waves would provide rich information about merger events. Among the possible electromagnetic counterparts from BH–NS mergers is the so-called kilonova/macronova, emission powered by the decay of radioactive r-process nuclei, which is one of the best targets for follow-up observations. We derive fitting formulas for the mass and the velocity of ejecta from a generic BH–NS merger based on recently performed numerical-relativity simulations. We combine these fitting formulas with a new semi-analytic model for a BH–NS kilonova/macronova lightcurve, which reproduces the results of radiation-transfer simulations. Specifically, the semi-analytic model reproduces the results of each band magnitude obtained by the previous radiation-transfer simulations within ∼1 mag. By using this semi-analytic model we found that, at 400 Mpc, the kilonova/macronova is as bright as 22–24 mag for cases with a small chirp mass and a high black hole spin, and >28 mag for a large chirp mass and a low black hole spin. We also apply our model to GRB 130603B as an illustration, and show that a BH–NS merger with a rapidly spinning black hole and a large neutron star radius is favored.

  19. Merger of binary neutron stars of unequal mass in full general relativity

    International Nuclear Information System (INIS)

    Shibata, Masaru; Taniguchi, Keisuke; Uryu-bar, Ko-barji

    2003-01-01

    We present results of three dimensional numerical simulations of the merger of unequal-mass binary neutron stars in full general relativity. A Γ-law equation of state P=(Γ-1)ρε is adopted, where P, ρ, ε, and Γ are the pressure, rest mass density, specific internal energy, and the adiabatic constant, respectively. We take Γ=2 and the baryon rest-mass ratio Q M to be in the range 0.85-1. The typical grid size is (633,633,317) for (x,y,z). We improve several implementations since the latest work. In the present code, the radiation reaction of gravitational waves is taken into account with a good accuracy. This fact enables us to follow the coalescence all the way from the late inspiral phase through the merger phase for which the transition is triggered by the radiation reaction. It is found that if the total rest mass of the system is more than ∼1.7 times of the maximum allowed rest mass of spherical neutron stars, a black hole is formed after the merger, irrespective of the mass ratios. The gravitational waveforms and outcomes in the merger of unequal-mass binaries are compared with those in equal-mass binaries. It is found that the disk mass around the so formed black holes increases with decreasing rest-mass ratios and decreases with increasing compactness of neutron stars. The merger process and the gravitational waveforms also depend strongly on the rest-mass ratios even for the range Q M =0.85-1

  20. General-relativistic Large-eddy Simulations of Binary Neutron Star Mergers

    Energy Technology Data Exchange (ETDEWEB)

    Radice, David, E-mail: dradice@astro.princeton.edu [Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540 (United States)

    2017-03-20

    The flow inside remnants of binary neutron star (NS) mergers is expected to be turbulent, because of magnetohydrodynamics instability activated at scales too small to be resolved in simulations. To study the large-scale impact of these instabilities, we develop a new formalism, based on the large-eddy simulation technique, for the modeling of subgrid-scale turbulent transport in general relativity. We apply it, for the first time, to the simulation of the late-inspiral and merger of two NSs. We find that turbulence can significantly affect the structure and survival time of the merger remnant, as well as its gravitational-wave (GW) and neutrino emissions. The former will be relevant for GW observation of merging NSs. The latter will affect the composition of the outflow driven by the merger and might influence its nucleosynthetic yields. The accretion rate after black hole formation is also affected. Nevertheless, we find that, for the most likely values of the turbulence mixing efficiency, these effects are relatively small and the GW signal will be affected only weakly by the turbulence. Thus, our simulations provide a first validation of all existing post-merger GW models.

  1. General Relativistic Simulations of Low-Mass Magnetized Binary Neutron Star Mergers

    Science.gov (United States)

    Giacomazzo, Bruno

    2017-01-01

    We will present general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) systems that produce long-lived neutron stars (NSs) after merger. While the standard scenario for short gamma-ray bursts (SGRBs) requires the formation after merger of a spinning black hole surrounded by an accretion disk, other theoretical models, such as the time-reversal scenario, predict the formation of a long-lived magnetar. The formation of a long-lived magnetar could in particular explain the X-ray plateaus that have been observed in some SGRBs. Moreover, observations of NSs with masses of 2 solar masses indicate that the equation of state of NS matter should support masses larger than that. Therefore a significant fraction of BNS mergers will produce long-lived NSs. This has important consequences both on the emission of gravitational wave signals and on their electromagnetic counterparts. We will discuss GRMHD simulations of ``low-mass'' magnetized BNS systems with different equations of state and mass ratios. We will describe the properties of their post-merger remnants and of their gravitational and electromagnetic emission.

  2. Resolved star formation on sub-galactic scales in a merger at z = 1.7

    International Nuclear Information System (INIS)

    Whitaker, Katherine E.; Rigby, Jane R.; Teng, Stacy H.; Brammer, Gabriel B.; Gladders, Michael D.; Sharon, Keren; Wuyts, Eva

    2014-01-01

    We present a detailed analysis of Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704. We measure the spatial variations of the extinction in RCS0327 through the observed Hγ/Hβ emission line ratios, finding a constant average extinction of E(B – V) gas = 0.40 ± 0.07. We infer that the star formation is enhanced as a result of an ongoing interaction, with measured star formation rates derived from demagnified, extinction-corrected Hβ line fluxes for the individual star-forming clumps falling >1-2 dex above the star formation sequence. When combining the HST/WFC3 [O III] λ5007/Hβ emission line ratio measurements with [N II]/Hα line ratios from Wuyts et al., we find that the majority of the individual star-forming regions fall along the local 'normal' abundance sequence. With the first detections of the He I λ5876 and He II λ4686 recombination lines in a distant galaxy, we probe the massive-star content of the star-forming regions in RCS0327. The majority of the star-forming regions have a He I λ5876 to Hβ ratio consistent with the saturated maximum value, which is only possible if they still contain hot O-stars. Two regions have lower ratios, implying that their last burst of new star formation ended ∼5 Myr ago. Together, the He I λ5876 and He II λ4686 to Hβ line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high-redshift merger. We place the spatial variations of the extinction, star formation rate and ionization conditions in the context of the star formation history of RCS0327.

  3. TIDAL TAILS OF MINOR MERGERS. II. COMPARING STAR FORMATION IN THE TIDAL TAILS OF NGC 2782

    Energy Technology Data Exchange (ETDEWEB)

    Knierman, Karen A.; Scowen, Paul; Veach, Todd; Groppi, Christopher [School of Earth and Space Exploration, Arizona State University, 550 E. Tyler Mall, Room PSF-686 (P.O. Box 871404), Tempe, AZ 85287-1404 (United States); Mullan, Brendan; Charlton, Jane [Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA (United States); Konstantopoulos, Iraklis [Australian Astronomical Observatory, P.O. Box 915, North Ryde NSW 1670 (Australia); Knezek, Patricia M., E-mail: karen.knierman@asu.edu, E-mail: paul.scowen@asu.edu, E-mail: tveach@asu.edu, E-mail: cgroppi@asu.edu, E-mail: mullan@astro.psu.edu, E-mail: iraklis@aao.gov.au, E-mail: pknezek@noao.edu [WIYN Consortium, Inc., 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)

    2013-09-10

    The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio {approx}4: 1 occurring {approx}200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and H{alpha} narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 {mu}m [C II] emission at the location of the three most luminous H{alpha} sources in the eastern tail, but not at the location of the even brighter H{alpha} source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and [C II] emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation.

  4. TIDAL TAILS OF MINOR MERGERS. II. COMPARING STAR FORMATION IN THE TIDAL TAILS OF NGC 2782

    International Nuclear Information System (INIS)

    Knierman, Karen A.; Scowen, Paul; Veach, Todd; Groppi, Christopher; Mullan, Brendan; Charlton, Jane; Konstantopoulos, Iraklis; Knezek, Patricia M.

    2013-01-01

    The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio ∼4: 1 occurring ∼200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and Hα narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 μm [C II] emission at the location of the three most luminous Hα sources in the eastern tail, but not at the location of the even brighter Hα source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and [C II] emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation

  5. The Next Generation of Numerical Modeling in Mergers- Constraining the Star Formation Law

    Science.gov (United States)

    Chien, Li-Hsin

    2010-09-01

    Spectacular images of colliding galaxies like the "Antennae", taken with the Hubble Space Telescope, have revealed that a burst of star/cluster formation occurs whenever gas-rich galaxies interact. A?The ages and locations of these clusters reveal the interaction history and provide crucial clues to the process of star formation in galaxies. A?We propose to carry out state-of-the-art numerical simulations to model six nearby galaxy mergers {Arp 256, NGC 7469, NGC 4038/39, NGC 520, NGC 2623, NGC 3256}, hence increasing the number with this level of sophistication by a factor of 3. These simulations provide specific predictions for the age and spatial distributions of young star clusters. The comparison between these simulation results and the observations will allow us to answer a number of fundamental questions including: 1} is shock-induced or density-dependent star formation the dominant mechanism; 2} are the demographics {i.e. mass and age distributions} of the clusters in different mergers similar, i.e. "universal", or very different; and 3} will it be necessary to include other mechanisms, e.g., locally triggered star formation, in the models to better match the observations?

  6. Illuminating gravitational waves: A concordant picture of photons from a neutron star merger

    Science.gov (United States)

    Kasliwal, M. M.; Nakar, E.; Singer, L. P.; Kaplan, D. L.; Cook, D. O.; Van Sistine, A.; Lau, R. M.; Fremling, C.; Gottlieb, O.; Jencson, J. E.; Adams, S. M.; Feindt, U.; Hotokezaka, K.; Ghosh, S.; Perley, D. A.; Yu, P.-C.; Piran, T.; Allison, J. R.; Anupama, G. C.; Balasubramanian, A.; Bannister, K. W.; Bally, J.; Barnes, J.; Barway, S.; Bellm, E.; Bhalerao, V.; Bhattacharya, D.; Blagorodnova, N.; Bloom, J. S.; Brady, P. R.; Cannella, C.; Chatterjee, D.; Cenko, S. B.; Cobb, B. E.; Copperwheat, C.; Corsi, A.; De, K.; Dobie, D.; Emery, S. W. K.; Evans, P. A.; Fox, O. D.; Frail, D. A.; Frohmaier, C.; Goobar, A.; Hallinan, G.; Harrison, F.; Helou, G.; Hinderer, T.; Ho, A. Y. Q.; Horesh, A.; Ip, W.-H.; Itoh, R.; Kasen, D.; Kim, H.; Kuin, N. P. M.; Kupfer, T.; Lynch, C.; Madsen, K.; Mazzali, P. A.; Miller, A. A.; Mooley, K.; Murphy, T.; Ngeow, C.-C.; Nichols, D.; Nissanke, S.; Nugent, P.; Ofek, E. O.; Qi, H.; Quimby, R. M.; Rosswog, S.; Rusu, F.; Sadler, E. M.; Schmidt, P.; Sollerman, J.; Steele, I.; Williamson, A. R.; Xu, Y.; Yan, L.; Yatsu, Y.; Zhang, C.; Zhao, W.

    2017-12-01

    Merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) with gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. Instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. We posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet.

  7. Gravitational wave spectroscopy of binary neutron star merger remnants with mode stacking

    Science.gov (United States)

    Yang, Huan; Paschalidis, Vasileios; Yagi, Kent; Lehner, Luis; Pretorius, Frans; Yunes, Nicolás

    2018-01-01

    A binary neutron star coalescence event has recently been observed for the first time in gravitational waves, and many more detections are expected once current ground-based detectors begin operating at design sensitivity. As in the case of binary black holes, gravitational waves generated by binary neutron stars consist of inspiral, merger, and postmerger components. Detecting the latter is important because it encodes information about the nuclear equation of state in a regime that cannot be probed prior to merger. The postmerger signal, however, can only be expected to be measurable by current detectors for events closer than roughly ten megaparsecs, which given merger rate estimates implies a low probability of observation within the expected lifetime of these detectors. We carry out Monte Carlo simulations showing that the dominant postmerger signal (the ℓ=m =2 mode) from individual binary neutron star mergers may not have a good chance of observation even with the most sensitive future ground-based gravitational wave detectors proposed so far (the Einstein Telescope and Cosmic Explorer, for certain equations of state, assuming a full year of operation, the latest merger rates, and a detection threshold corresponding to a signal-to-noise ratio of 5). For this reason, we propose two methods that stack the postmerger signal from multiple binary neutron star observations to boost the postmerger detection probability. The first method follows a commonly used practice of multiplying the Bayes factors of individual events. The second method relies on an assumption that the mode phase can be determined from the inspiral waveform, so that coherent mode stacking of the data from different events becomes possible. We find that both methods significantly improve the chances of detecting the dominant postmerger signal, making a detection very likely after a year of observation with Cosmic Explorer for certain equations of state. We also show that in terms of detection

  8. Tracking the Obscured Star Formation Along the Complete Evolutionary Merger Sequence of LIRGs

    Science.gov (United States)

    Diaz-Santos, Tanio

    2014-10-01

    We propose to obtain WFC3 narrow-band Pa-beta imaging of a sample of 24 nearby luminous infrared (IR) galaxies (LIRGs) from the Great Observatories All-sky LIRG survey (GOALS) selected to be in advanced stages of interaction. LIRGs account for half of the obscured star formation of the Universe at z ~ 1-2, and they represent a key population in galaxy formation and evolution. We will use the Pa-beta images to trace the ionized gas in LIRGs and study its spatial distribution from scales of ~ 100 pc to up to several kpc, probing the youngest, massive stars formed in the most buried environments of LIRGs due to the interaction process. This will allow us to measure how the gas in the center of mergers is converted into stars, which eventually leads to the build-up of a nuclear stellar cusp and the "inside-out" growth of bulges. We will also create spatially-resolved Pa-beta equivalent width maps to search for age gradients across the galaxies and correlate the distribution of Pa-beta emission with that of un-obscured star clusters detected in the UV and optical with HST on the same spatial scales. Finally, we will combine our data with previous studies mainly focused on isolated and early-stage interacting LIRG systems to analyze the size and compactness of the starburst along the complete merger sequence of LIRGs. The requested data represent a critical missing piece of information that will allow us to understand both the physics of merger-induced star formation and the applicability of local LIRGs as templates for high-z interacting starburst galaxies.

  9. Rates of short-GRB afterglows in association with binary neutron star mergers

    Science.gov (United States)

    Saleem, M.; Pai, Archana; Misra, Kuntal; Resmi, L.; Arun, K. G.

    2018-03-01

    Assuming all binary neutron star (BNS) mergers produce short gamma-ray bursts, we combine the merger rates of BNS from population synthesis studies, the sensitivities of advanced gravitational wave (GW) interferometer networks, and of the electromagnetic (EM) facilities in various wavebands, to compute the detection rate of associated afterglows in these bands. Using the inclination angle measured from GWs as a proxy for the viewing angle and assuming a uniform distribution of jet opening angle between 3° and 30°, we generate light curves of the counterparts using the open access afterglow hydrodynamics package BOXFIT for X-ray, optical, and radio bands. For different EM detectors, we obtain the fraction of EM counterparts detectable in these three bands by imposing appropriate detection thresholds. In association with BNS mergers detected by five (three) detector networks of advanced GW interferometers, assuming a BNS merger rate of 0.6-774 Gpc-3 yr-1 from population synthesis models, we find the afterglow detection rates (per year) to be 0.04-53 (0.02-27), 0.03-36 (0.01-19), and 0.04-47 (0.02-25) in the X-ray, optical, and radio bands, respectively. Our rates represent maximum possible detections for the given BNS rate since we ignore effects of cadence and field of view in EM follow-up observations.

  10. The influence of thermal pressure on equilibrium models of hypermassive neutron star merger remnants

    Energy Technology Data Exchange (ETDEWEB)

    Kaplan, J. D.; Ott, C. D.; Roberts, L. [TAPIR, California Institute of Technology, Mailcode 350-17, Pasadena, CA 91125 (United States); O' Connor, E. P. [CITA, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Kiuchi, K. [Yukawa Institute for Theoretical Physics, University of Kyoto, Kyoto (Japan); Duez, M., E-mail: cott@tapir.caltech.edu [Department of Physics and Astronomy, Washington State University, Pullman, WA (United States)

    2014-07-20

    The merger of two neutron stars leaves behind a rapidly spinning hypermassive object whose survival is believed to depend on the maximum mass supported by the nuclear equation of state (EOS), angular momentum redistribution by (magneto-)rotational instabilities, and spindown by gravitational waves. The high temperatures (∼5-40 MeV) prevailing in the merger remnant may provide thermal pressure support that could increase its maximum mass and, thus, its life on a neutrino-cooling timescale. We investigate the role of thermal pressure support in hypermassive merger remnants by computing sequences of spherically symmetric and axisymmetric uniformly and differentially rotating equilibrium solutions to the general-relativistic stellar structure equations. Using a set of finite-temperature nuclear EOS, we find that hot maximum-mass critically spinning configurations generally do not support larger baryonic masses than their cold counterparts. However, subcritically spinning configurations with mean density of less than a few times nuclear saturation density yield a significantly thermally enhanced mass. Even without decreasing the maximum mass, cooling and other forms of energy loss can drive the remnant to an unstable state. We infer secular instability by identifying approximate energy turning points in equilibrium sequences of constant baryonic mass parameterized by maximum density. Energy loss carries the remnant along the direction of decreasing gravitational mass and higher density until instability triggers collapse. Since configurations with more thermal pressure support are less compact and thus begin their evolution at a lower maximum density, they remain stable for longer periods after merger.

  11. The influence of thermal pressure on equilibrium models of hypermassive neutron star merger remnants

    International Nuclear Information System (INIS)

    Kaplan, J. D.; Ott, C. D.; Roberts, L.; O'Connor, E. P.; Kiuchi, K.; Duez, M.

    2014-01-01

    The merger of two neutron stars leaves behind a rapidly spinning hypermassive object whose survival is believed to depend on the maximum mass supported by the nuclear equation of state (EOS), angular momentum redistribution by (magneto-)rotational instabilities, and spindown by gravitational waves. The high temperatures (∼5-40 MeV) prevailing in the merger remnant may provide thermal pressure support that could increase its maximum mass and, thus, its life on a neutrino-cooling timescale. We investigate the role of thermal pressure support in hypermassive merger remnants by computing sequences of spherically symmetric and axisymmetric uniformly and differentially rotating equilibrium solutions to the general-relativistic stellar structure equations. Using a set of finite-temperature nuclear EOS, we find that hot maximum-mass critically spinning configurations generally do not support larger baryonic masses than their cold counterparts. However, subcritically spinning configurations with mean density of less than a few times nuclear saturation density yield a significantly thermally enhanced mass. Even without decreasing the maximum mass, cooling and other forms of energy loss can drive the remnant to an unstable state. We infer secular instability by identifying approximate energy turning points in equilibrium sequences of constant baryonic mass parameterized by maximum density. Energy loss carries the remnant along the direction of decreasing gravitational mass and higher density until instability triggers collapse. Since configurations with more thermal pressure support are less compact and thus begin their evolution at a lower maximum density, they remain stable for longer periods after merger.

  12. Constraining the equation of state of neutron stars from binary mergers.

    Science.gov (United States)

    Takami, Kentaro; Rezzolla, Luciano; Baiotti, Luca

    2014-08-29

    Determining the equation of state of matter at nuclear density and hence the structure of neutron stars has been a riddle for decades. We show how the imminent detection of gravitational waves from merging neutron star binaries can be used to solve this riddle. Using a large number of accurate numerical-relativity simulations of binaries with nuclear equations of state, we find that the postmerger emission is characterized by two distinct and robust spectral features. While the high-frequency peak has already been associated with the oscillations of the hypermassive neutron star produced by the merger and depends on the equation of state, a new correlation emerges between the low-frequency peak, related to the merger process, and the total compactness of the stars in the binary. More importantly, such a correlation is essentially universal, thus providing a powerful tool to set tight constraints on the equation of state. If the mass of the binary is known from the inspiral signal, the combined use of the two frequency peaks sets four simultaneous constraints to be satisfied. Ideally, even a single detection would be sufficient to select one equation of state over the others. We test our approach with simulated data and verify it works well for all the equations of state considered.

  13. Detectable radio flares following gravitational waves from mergers of binary neutron stars.

    Science.gov (United States)

    Nakar, Ehud; Piran, Tsvi

    2011-09-28

    Mergers of neutron-star/neutron-star binaries are strong sources of gravitational waves. They can also launch subrelativistic and mildly relativistic outflows and are often assumed to be the sources of short γ-ray bursts. An electromagnetic signature that persisted for weeks to months after the event would strengthen any future claim of a detection of gravitational waves. Here we present results of calculations showing that the interaction of mildly relativistic outflows with the surrounding medium produces radio flares with peak emission at 1.4 gigahertz that persist at detectable (submillijansky) levels for weeks, out to a redshift of 0.1. Slower subrelativistic outflows produce flares detectable for years at 150 megahertz, as well as at 1.4 gigahertz, from slightly shorter distances. The radio transient RT 19870422 (ref. 11) has the properties predicted by our model, and its most probable origin is the merger of a compact neutron-star/neutron-star binary. The lack of radio detections usually associated with short γ-ray bursts does not constrain the radio transients that we discuss here (from mildly relativistic and subrelativistic outflows) because short γ-ray burst redshifts are typically >0.1 and the appropriate timescales (longer than weeks) have not been sampled.

  14. TIDAL TAILS OF MINOR MERGERS: STAR FORMATION EFFICIENCY IN THE WESTERN TAIL OF NGC 2782

    International Nuclear Information System (INIS)

    Knierman, Karen; Scowen, Paul; Jansen, Rolf A.; Knezek, Patricia M.; Wehner, Elizabeth

    2012-01-01

    While major mergers and their tidal debris are well studied, they are less common than minor mergers (mass ratios ∼ SFR ) to be several orders of magnitude less than expected from the total gas density. Together with extended FUV+NUV emission from Galaxy Evolution Explorer along the tail, this indicates a low global star formation efficiency in the tidal tail producing lower mass star clusters. The H II region that we observed has a local (few-kiloparsec scale) Σ SFR from Hα that is less than that expected from the total gas density, which is consistent with other observations of tidal debris. The star formation efficiency of this H II region inferred from the total gas density is low, but normal when inferred from the molecular gas density. These results suggest the presence of a very small, locally dense region in the western tail of NGC 2782 or of a low-metallicity and/or low-pressure star-forming region.

  15. Dark-matter halo mergers as a fertile environment for low-mass Population III star formation

    DEFF Research Database (Denmark)

    Bovino, S.; Latif, M. A.; Grassi, Tommaso

    2014-01-01

    While Population III (Pop III) stars are typically thought to be massive, pathways towards lower mass Pop III stars may exist when the cooling of the gas is particularly enhanced. A possible route is enhanced HD cooling during the merging of dark-matter haloes. The mergers can lead to a high ioni...

  16. Evolution of the Black Hole Mass Function in Star Clusters from Multiple Mergers

    Science.gov (United States)

    Christian, Pierre; Mocz, Philip; Loeb, Abraham

    2018-05-01

    We investigate the effects of black hole (BH) mergers in star clusters on the black hole mass function (BHMF). As BHs are not produced in pair-instability supernovae, it is suggested that there is a dearth of high-mass stellar BHs. This dearth generates a gap in the upper end of the BHMF. Meanwhile, parameter fitting of X-ray binaries suggests the existence of a gap in the mass function under 5 solar masses. We show, through evolving a coagulation equation, that BH mergers can appreciably fill the upper mass gap, and that the lower mass gap generates potentially observable features at larger mass scales. We also explore the importance of ejections in such systems and whether dynamical clusters can be formation sites of intermediate-mass BH seeds.

  17. Multi-messenger observations of a binary neutron star merger

    Czech Academy of Sciences Publication Activity Database

    Abbott, P.B.; Abbott, R.; Abbott, T.D.; Blažek, Jiří; Boháčová, Martina; Caballero-García, María Dolores; Chudoba, Jiří; Ebr, Jan; Jelínek, Martin; Juryšek, Jakub; Kubánek, Petr; Mandát, Dušan; Palatka, Miroslav; Pech, Miroslav; Prouza, Michael; Řídký, Jan; Martins dos Santos, Eva M.; Schovánek, Petr; Trávníček, Petr; Vícha, Jakub; Yushkov, Alexey

    2017-01-01

    Roč. 848, č. 2 (2017), s. 1-59, č. článku L12. ISSN 2041-8205 R&D Projects: GA MŠk LM2015038; GA MŠk LG15014; GA MŠk EF16_013/0001402 Grant - others:OP VVV - AUGER-CZ(XE) CZ.02.1.01/0.0/0.0/16_013/0001402 Institutional support: RVO:68378271 ; RVO:67985815 Keywords : gravitational waves * stars: neutron Subject RIV: BF - Elementary Particles and High Energy Physics; BN - Astronomy, Celestial Mechanics, Astrophysics (ASU-R) OBOR OECD: Particles and field physics; Astronomy (including astrophysics,space science) (ASU-R) Impact factor: 5.522, year: 2016

  18. UPPER LIMITS ON THE RATES OF BINARY NEUTRON STAR AND NEUTRON STAR-BLACK HOLE MERGERS FROM ADVANCED LIGO'S FIRST OBSERVING RUN

    NARCIS (Netherlands)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, E.; Ackley, K.; Adams, C.; Phythian-Adams, A.T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.T.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, R.D.; Barone, E.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, M.J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, A.L.S.; Bock, O.; Boer, M.; Bogaert, J.G.; Bogan, C.; Bohe, A.; Bond, T.C; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, A.D.; Brown, D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderon Bustillo, J.; Callister, T. A.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglia, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, D. S.; Chen, Y; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Qian; Chua, S. E.; Chung, E.S.; Ciani, G.; Clara, E.; Clark, J. A.; Cleva, E.; Coccia, E.; Cohadon, P. -E; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M., Jr.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, A.C.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J. -P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, A.L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; Debra, D.; Debreczeni, G.; Degallaix, J.; De laurentis, M.; Deleglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.A.; Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Diaz, M. C.; Di Fiore, L.; Giovanni, M.G.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H. -B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, T. M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.M.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M; Fournier, J. -D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garunfi, E.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.P.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; Gonzalez, R.G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Lee-Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.M.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Buffoni-Hall, R.; Hall, E. D.; Hammond, G.L.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, P.J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C. -J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Henry, J.A.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J. -M.; Isi, M.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, D.H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; Jimenez-Forteza, E.; Johnson, W.; Jones, I.D.; Jones, R.; Jonker, R. J. G.; Ju, L.; Haris, K.; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.H.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kefelian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.E.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan., S.; Khan, Z.; Khazanov, E. A.; Kusunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, Namjun; Kim, W.; Kim, Y.M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kissel, J. S.; Klein, B.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Krishnan, B.; Krolak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kumar, R.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzar, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C.H.; Lee, K.H.; Lee, M.H.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Lewis, J. B.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Lombardi, A. L.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Luck, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magana-Sandoval, F.; Zertuche, L. Magana; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, E.; Marion, F.; Marka, S.; Marka, Z.; Markosyan, A. S.; Maros, E.; Martelli, E.; Martellini, L.; Martin, I. W.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, A. L.; Miller, B.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B.C.; Moore, J.C.; Moraru, D.; Gutierrez Moreno, M.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, S.D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P.G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; Gutierrez-Neri, M.; Neunzert, A.; Newton-Howes, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Deill, J.; Oelker, E.; Ogin, G. H.; Oh, J.; Oh, S. H.; Ohme, F.; Oliver, M. B.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, E.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.S; Pascucci, D.; Pasqualetti, A.; Passahieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Perri, L. M.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Proxhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Purrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, E. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Rizzo, D.M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romanov, G.; Romie, J. H.; Rosinska, D.; Rowan, S.; Rudiger, A.; Ruggi, P.; Ryan, K.A.; Sachdev, P.S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J; Schmidt, P.; Schnabel, R.B.; Schofield, R. M. S.; Schonbecx, A.; Schreiber, K.E.C.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, M.S.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T. J.; Shahriar, M. S.; Shaltevi, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, António Dias da; Singer, A; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, R. J. E.; Smith, N.D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stone, J.R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S. E.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Sutton, P. J.; Swinkels, B. L.; Szczepanczyk, M. J.; Tacca, M.D.; Talukder, D.; Tanner, D. B.; Tapai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, W.R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Toxmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; Torres, C. V.; Torrie, C. I.; Toyra, D.; Travasso, F.; Traylor, G.; Trifiro, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.G.; van den Brand, J. E. J.; Van Den Broeck, C.F.F.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heuningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasuth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P.J.; Venkateswara, K.; Verkindt, D.; Vetrano, E.; Vicere, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J. -Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, MT; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L. -W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.M.; Wessels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Williams, D.R.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Worden, J.; Wright, J.L.; Wu, D.S.; Wu, G.; Yablong, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; Zadrozny, A.; Zangrando, L.; Zanolin, M.; Zendri, J. -P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.

    2016-01-01

    We report here the non-detection of gravitational waves from the merger of binary-neutron star systems and neutron star-black hole systems during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). In particular, we searched for gravitational-wave

  19. Enrichment of r-Process Elements by Neutron Star Mergers through the Sub-Halo Clustering

    Science.gov (United States)

    Ishimaru, Yuhri; Ojima, Takuya; Wanajo, Shinya; Prantzos, Nikos

    Neutron star mergers (NSMs) are suggested to be the most plausible site of r-process by nucleosynthesis studies, while previous chemical evolution models pointed out that the long lifetimes of NS binaries are in conflict with the observed [r/Fe] of the Galactic halo stars. We attempt to solve this problem, assuming the Galactic halo was formed from merging sub-halos. We find that [r/Fe] start increasing at [Fe/H] < -3, if the star formation efficiencies are smaller for less massive sub-halos. We also show that small numbers of NSMs for least massive sub-halos could cause the large enhancement of [r/Fe]. Our results support NSMs as the major site of r-process.

  20. Insight-HXMT observations of the first binary neutron star merger GW170817

    Science.gov (United States)

    Li, TiPei; Xiong, ShaoLin; Zhang, ShuangNan; Lu, FangJun; Song, LiMing; Cao, XueLei; Chang, Zhi; Chen, Gang; Chen, Li; Chen, TianXiang; Chen, Yong; Chen, YiBao; Chen, YuPeng; Cui, Wei; Cui, WeiWei; Deng, JingKang; Dong, YongWei; Du, YuanYuan; Fu, MinXue; Gao, GuanHua; Gao, He; Gao, Min; Ge, MingYu; Gu, YuDong; Guan, Ju; Guo, ChengCheng; Han, DaWei; Hu, Wei; Huang, Yue; Huo, Jia; Jia, ShuMei; Jiang, LuHua; Jiang, WeiChun; Jin, Jing; Jin, YongJie; Li, Bing; Li, ChengKui; Li, Gang; Li, MaoShun; Li, Wei; Li, Xian; Li, XiaoBo; Li, XuFang; Li, YanGuo; Li, ZiJian; Li, ZhengWei; Liang, XiaoHua; Liao, JinYuan; Liu, CongZhan; Liu, GuoQing; Liu, HongWei; Liu, ShaoZhen; Liu, XiaoJing; Liu, Yuan; Liu, YiNong; Lu, Bo; Lu, XueFeng; Luo, Tao; Ma, Xiang; Meng, Bin; Nang, Yi; Nie, JianYin; Ou, Ge; Qu, JinLu; Sai, Na; Sun, Liang; Tan, Yin; Tao, Lian; Tao, WenHui; Tuo, YouLi; Wang, GuoFeng; Wang, HuanYu; Wang, Juan; Wang, WenShuai; Wang, YuSa; Wen, XiangYang; Wu, BoBing; Wu, Mei; Xiao, GuangCheng; Xu, He; Xu, YuPeng; Yan, LinLi; Yang, JiaWei; Yang, Sheng; Yang, YanJi; Zhang, AiMei; Zhang, ChunLei; Zhang, ChengMo; Zhang, Fan; Zhang, HongMei; Zhang, Juan; Zhang, Qiang; Zhang, Shu; Zhang, Tong; Zhang, Wei; Zhang, WanChang; Zhang, WenZhao; Zhang, Yi; Zhang, Yue; Zhang, YiFei; Zhang, YongJie; Zhang, Zhao; Zhang, ZiLiang; Zhao, HaiSheng; Zhao, JianLing; Zhao, XiaoFan; Zheng, ShiJie; Zhu, Yue; Zhu, YuXuan; Zou, ChangLin

    2018-03-01

    Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area ( 1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints ( 10‒7 to 10‒6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.

  1. Gravitational Waves from Binary Black Hole Mergers inside Stars.

    Science.gov (United States)

    Fedrow, Joseph M; Ott, Christian D; Sperhake, Ulrich; Blackman, Jonathan; Haas, Roland; Reisswig, Christian; De Felice, Antonio

    2017-10-27

    We present results from a controlled numerical experiment investigating the effect of stellar density gas on the coalescence of binary black holes (BBHs) and the resulting gravitational waves (GWs). This investigation is motivated by the proposed stellar core fragmentation scenario for BBH formation and the associated possibility of an electromagnetic counterpart to a BBH GW event. We employ full numerical relativity coupled with general-relativistic hydrodynamics and set up a 30+30  M_{⊙} BBH (motivated by GW150914) inside gas with realistic stellar densities. Our results show that at densities ρ≳10^{6}-10^{7}  g cm^{-3} dynamical friction between the BHs and gas changes the coalescence dynamics and the GW signal in an unmistakable way. We show that for GW150914, LIGO observations appear to rule out BBH coalescence inside stellar gas of ρ≳10^{7}  g cm^{-3}. Typical densities in the collapsing cores of massive stars are in excess of this density. This excludes the fragmentation scenario for the formation of GW150914.

  2. Simulating neutron star mergers as r-process sources in ultrafaint dwarf galaxies

    Science.gov (United States)

    Safarzadeh, Mohammadtaher; Scannapieco, Evan

    2017-10-01

    To explain the high observed abundances of r-process elements in local ultrafaint dwarf (UFD) galaxies, we perform cosmological zoom simulations that include r-process production from neutron star mergers (NSMs). We model star formation stochastically and simulate two different haloes with total masses ≈108 M⊙ at z = 6. We find that the final distribution of [Eu/H] versus [Fe/H] is relatively insensitive to the energy by which the r-process material is ejected into the interstellar medium, but strongly sensitive to the environment in which the NSM event occurs. In one halo, the NSM event takes place at the centre of the stellar distribution, leading to high levels of r-process enrichment such as seen in a local UFD, Reticulum II (Ret II). In a second halo, the NSM event takes place outside of the densest part of the galaxy, leading to a more extended r-process distribution. The subsequent star formation occurs in an interstellar medium with shallow levels of r-process enrichment that results in stars with low levels of [Eu/H] compared to Ret II stars even when the maximum possible r-process mass is assumed to be ejected. This suggests that the natal kicks of neutron stars may also play an important role in determining the r-process abundances in UFD galaxies, a topic that warrants further theoretical investigation.

  3. Realistic fission models, new beta-decay half-lives and the r-process in neutron star mergers

    International Nuclear Information System (INIS)

    Shibagaki, S.; Kajino, T.; Chiba, S.; Lorusso, G.; Nishimura, S.; Mathews, G. J.

    2014-01-01

    Almost half of heavy nuclei beyond iron are considered to be produced by rapid neutron capture process (r-process). This process occurs in the neutron-rich environment such as core-collapse supernovae or neutron star mergers, but the main production site is still unknown. In the r-process of neutron star mergers, nuclear fission reactions play an important role. Also beta-decay half-lives of magic nuclei are crucial for the r-process. We have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions and new beta-decay half-lives for N=82 nuclei measured at RIBF-RIKEN. We investigate the effect of nuclear fission on abundance patterns in the matter ejected from neutron star mergers with two different fission fragment mass distributions. We also discuss how the new experimental beta-decay half-lives affect the r-process

  4. An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system.

    Science.gov (United States)

    Burgay, M; D'Amico, N; Possenti, A; Manchester, R N; Lyne, A G; Joshi, B C; McLaughlin, M A; Kramer, M; Sarkissian, J M; Camilo, F; Kalogera, V; Kim, C; Lorimer, D R

    2003-12-04

    The merger of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity. A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low, because we know of only a few double-neutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737-3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737-3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe).

  5. GW170817 and the Prospect of Forming Supramassive Remnants in Neutron Star Mergers

    Science.gov (United States)

    Ma, Peng-Xiong; Jiang, Jin-Liang; Wang, Hao; Jin, Zhi-Ping; Fan, Yi-Zhong; Wei, Da-Ming

    2018-05-01

    The gravitational wave data of GW170817 favor the equation of state (EoS) models that predict compact neutron stars (NSs), consistent with the radius constraints from X-ray observations. Motivated by such remarkable progress, we examine the fate of the remnants formed in NS mergers and focus on the roles of the angular momentum and the mass distribution of the binary NSs. In the mass-shedding limit (for which the dimensionless angular momentum equals the Keplerian value, i.e., j = j Kep), the adopted seven EoS models, except for H4 and ALF2, yield supramassive NSs in more than half of the mergers. However, for j ≲ 0.7 j Kep, the presence or absence of a non-negligible fraction of supramassive NSs formed in the mergers depends sensitively on both the EoS and the mass distribution of the binary systems. The NS mergers with a total gravitational mass ≤ 2.6 M ⊙ are found to be able to shed valuable light on both the EoS model and the angular momentum of the remnants if supramassive NSs are still absent. We have also discussed the uncertainty on estimating the maximum gravitational mass of nonrotating NSs (M max) due to the unknown j of the precollapse remnants. With the data of GW170817 and the assumption of the mass loss of 0.03 M ⊙, we have M max < (2.19, 2.32) M ⊙ (90% confidence level) for j = (1.0, 0.8) j Kep, respectively.

  6. Gravitational waves and neutrino emission from the merger of binary neutron stars.

    Science.gov (United States)

    Sekiguchi, Yuichiro; Kiuchi, Kenta; Kyutoku, Koutarou; Shibata, Masaru

    2011-07-29

    Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating a finite-temperature (Shen's) equation of state (EOS) and neutrino cooling for the first time. It is found that for this stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime (≫10  ms) is the outcome for the total mass ≲3.0M(⊙). It is shown that the typical total neutrino luminosity of the HMNS is ∼3-8×10(53)  erg/s and the effective amplitude of gravitational waves from the HMNS is 4-6×10(-22) at f=2.1-2.5  kHz for a source distance of 100 Mpc. We also present the neutrino luminosity curve when a black hole is formed for the first time.

  7. Post-merger evolution of a neutron star-black hole binary with neutrino transport

    Science.gov (United States)

    Foucart, Francois; O'Connor, Evan; Roberts, Luke; Duez, Matthew D.; Haas, Roland; Kidder, Lawrence E.; Ott, Christian D.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela

    2015-06-01

    We present a first simulation of the post-merger evolution of a black hole-neutron star binary in full general relativity using an energy-integrated general-relativistic truncated moment formalism for neutrino transport. We describe our implementation of the moment formalism and important tests of our code, before studying the formation phase of an accretion disk after a black hole-neutron star merger. We use as initial data an existing general-relativistic simulation of the merger of a neutron star of mass 1.4 M⊙ with a black hole of mass 7 M⊙ and dimensionless spin χBH=0.8 . Comparing with a simpler leakage scheme for the treatment of the neutrinos, we find noticeable differences in the neutron-to-proton ratio in and around the disk, and in the neutrino luminosity. We find that the electron neutrino luminosity is much lower in the transport simulations, and that both the disk and the disk outflows are less neutron rich. The spatial distribution of the neutrinos is significantly affected by relativistic effects, due to large velocities and curvature in the regions of strongest emission. Over the short time scale evolved, we do not observe purely neutrino-driven outflows. However, a small amount of material (3 ×10-4M⊙ ) is ejected in the polar region during the circularization of the disk. Most of that material is ejected early in the formation of the disk, and is fairly neutron rich (electron fraction Ye˜0.15 - 0.25 ). Through r-process nucleosynthesis, that material should produce high-opacity lanthanides in the polar region, and could thus affect the light curve of radioactively powered electromagnetic transients. We also show that by the end of the simulation, while the bulk of the disk remains neutron rich (Ye˜0.15 - 0.2 and decreasing), its outer layers have a higher electron fraction: 10% of the remaining mass has Ye>0.3 . As that material would be the first to be unbound by disk outflows on longer time scales, and as composition evolution is

  8. Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-radiation Hydrodynamics Study

    Science.gov (United States)

    Fujibayashi, Sho; Kiuchi, Kenta; Nishimura, Nobuya; Sekiguchi, Yuichiro; Shibata, Masaru

    2018-06-01

    We perform long-term general relativistic neutrino radiation hydrodynamics simulations (in axisymmetry) for a massive neutron star (MNS) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. We take into account the effects of viscosity, which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. The viscous effect plays key roles for the mass ejection from the remnant in two phases of the evolution. In the first t ≲ 10 ms, a differential rotation state of the MNS is changed to a rigidly rotating state. A shock wave caused by the variation of its quasi-equilibrium state induces significant mass ejection of mass ∼(0.5–2.0) × {10}-2 {M}ȯ for the α-viscosity parameter of 0.01–0.04. For the longer-term evolution with ∼0.1–10 s, a significant fraction of the torus material is ejected. We find that the total mass of the viscosity-driven ejecta (≳ {10}-2 {M}ȯ ) could dominate over that of the dynamical ejecta (≲ {10}-2 {M}ȯ ). The electron fraction, Y e , of the ejecta is always high enough (Y e ≳ 0.25) that this post-merger ejecta is lanthanide-poor; hence, the opacity of the ejecta is likely to be ∼10–100 times lower than that of the dynamical ejecta. This indicates that the electromagnetic signal from the ejecta would be rapidly evolving, bright, and blue if it is observed from a small viewing angle (≲45°) for which the effect of the dynamical ejecta is minor.

  9. Localization of binary neutron star mergers with second and third generation gravitational-wave detectors

    Science.gov (United States)

    Mills, Cameron; Tiwari, Vaibhav; Fairhurst, Stephen

    2018-05-01

    The observation of gravitational wave signals from binary black hole and binary neutron star mergers has established the field of gravitational wave astronomy. It is expected that future networks of gravitational wave detectors will possess great potential in probing various aspects of astronomy. An important consideration for successive improvement of current detectors or establishment on new sites is knowledge of the minimum number of detectors required to perform precision astronomy. We attempt to answer this question by assessing the ability of future detector networks to detect and localize binary neutron stars mergers on the sky. Good localization ability is crucial for many of the scientific goals of gravitational wave astronomy, such as electromagnetic follow-up, measuring the properties of compact binaries throughout cosmic history, and cosmology. We find that although two detectors at improved sensitivity are sufficient to get a substantial increase in the number of observed signals, at least three detectors of comparable sensitivity are required to localize majority of the signals, typically to within around 10 deg2 —adequate for follow-up with most wide field of view optical telescopes.

  10. Strange Quark Stars in Binaries: Formation Rates, Mergers, and Explosive Phenomena

    International Nuclear Information System (INIS)

    Wiktorowicz, G.; Drago, A.; Pagliara, G.; Popov, S. B.

    2017-01-01

    Recently, the possible coexistence of a first family composed of “normal” neutron stars (NSs) with a second family of strange quark stars (QSs) has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. In this paper, we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and NSs in different subpopulations. We incorporate the strange QS formation model provided by the two-families scenario, and we perform a large-scale population synthesis study in order to obtain the population characteristics. According to our results, the main channel for strange QS formation in binary systems is accretion from a secondary companion on an NS. Therefore, a rather large number of strange QSs form by accretion in low-mass X-ray binaries and this opens the possibility of having explosive GRB-like phenomena not related to supernovae and not due to the merger of two NSs. The number of double strange QS systems is rather small, with only a tiny fraction that merge within a Hubble time. This drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from Earth and lunar experiments. Moreover, this value of the flux rules out at least one relevant channel for the transformation of all NSs into strange QSs by strangelets’ absorption.

  11. Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

    Science.gov (United States)

    Paul, Debdutta

    2018-04-01

    The luminosity function of short Gamma Ray Bursts (GRBs) is modelled by using the available catalogue data of all short GRBs (sGRBs) detected till October, 2017. The luminosities are estimated via the `pseudo-redshifts' obtained from the `Yonetoku correlation', assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. While the simple powerlaw is ruled out to high confidence, the data is fit well both by exponential cutoff powerlaw and broken powerlaw models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of short GRBs are derived. Assuming a short GRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present and future configurations of the GW detector networks. Stringent lower limits of 1.87yr-1 for the aLIGO-VIRGO, and 3.11yr-1 for the upcoming aLIGO-VIRGO-KAGRA-LIGO/India configurations are thus derived for the BNSM rate at 68% confidence. The BNSM rates calculated from this work and that independently inferred from the observation of the only confirmed BNSM observed till date, are shown to have a mild tension; however the scenario that all BNSMs produce sGRBs cannot be ruled out.

  12. Strange Quark Stars in Binaries: Formation Rates, Mergers, and Explosive Phenomena

    Science.gov (United States)

    Wiktorowicz, G.; Drago, A.; Pagliara, G.; Popov, S. B.

    2017-09-01

    Recently, the possible coexistence of a first family composed of “normal” neutron stars (NSs) with a second family of strange quark stars (QSs) has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. In this paper, we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and NSs in different subpopulations. We incorporate the strange QS formation model provided by the two-families scenario, and we perform a large-scale population synthesis study in order to obtain the population characteristics. According to our results, the main channel for strange QS formation in binary systems is accretion from a secondary companion on an NS. Therefore, a rather large number of strange QSs form by accretion in low-mass X-ray binaries and this opens the possibility of having explosive GRB-like phenomena not related to supernovae and not due to the merger of two NSs. The number of double strange QS systems is rather small, with only a tiny fraction that merge within a Hubble time. This drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from Earth and lunar experiments. Moreover, this value of the flux rules out at least one relevant channel for the transformation of all NSs into strange QSs by strangelets’ absorption.

  13. Strange Quark Stars in Binaries: Formation Rates, Mergers, and Explosive Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Wiktorowicz, G. [Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw (Poland); Drago, A.; Pagliara, G. [Dipartimento di Fisica e Scienze della Terra dell’Università di Ferrara and INFN Sezione di Ferrara, Via Saragat 1, I-44100 Ferrara (Italy); Popov, S. B., E-mail: gwiktoro@astrouw.edu.pl [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetsky prospekt 13, 119234, Moscow (Russian Federation)

    2017-09-10

    Recently, the possible coexistence of a first family composed of “normal” neutron stars (NSs) with a second family of strange quark stars (QSs) has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. In this paper, we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and NSs in different subpopulations. We incorporate the strange QS formation model provided by the two-families scenario, and we perform a large-scale population synthesis study in order to obtain the population characteristics. According to our results, the main channel for strange QS formation in binary systems is accretion from a secondary companion on an NS. Therefore, a rather large number of strange QSs form by accretion in low-mass X-ray binaries and this opens the possibility of having explosive GRB-like phenomena not related to supernovae and not due to the merger of two NSs. The number of double strange QS systems is rather small, with only a tiny fraction that merge within a Hubble time. This drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from Earth and lunar experiments. Moreover, this value of the flux rules out at least one relevant channel for the transformation of all NSs into strange QSs by strangelets’ absorption.

  14. A Neutron Star Binary Merger Model for GW170817/GRB 170817A/SSS17a

    Energy Technology Data Exchange (ETDEWEB)

    Murguia-Berthier, A.; Ramirez-Ruiz, E.; Kilpatrick, C. D.; Foley, R. J.; Coulter, D. A.; Pan, Y.-C.; Prochaska, J. X.; Rojas-Bravo, C.; Siebert, M. R. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Kasen, D. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Lee, W. H. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Circuito Exterior, C.U., A. Postal 70-264, 04510 Cd. de México, México (Mexico); Piro, A. L.; Drout, M. R.; Madore, B. F.; Shappee, B. J.; Simon, J. D. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Rest, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2017-10-20

    The merging neutron star gravitational-wave event GW170817 has been observed throughout the entire electromagnetic spectrum from radio waves to γ -rays. The resulting energetics, variability, and light curves are shown to be consistent with GW170817 originating from the merger of two neutron stars, in all likelihood followed by the prompt gravitational collapse of the massive remnant. The available γ -ray, X-ray, and radio data provide a clear probe for the nature of the relativistic ejecta and the non-thermal processes occurring within, while the ultraviolet, optical, and infrared emission are shown to probe material torn during the merger and subsequently heated by the decay of freshly synthesized r -process material. The simplest hypothesis, that the non-thermal emission is due to a low-luminosity short γ -ray burst (sGRB), seems to agree with the present data. While low-luminosity sGRBs might be common, we show here that the collective prompt and multi-wavelength observations are also consistent with a typical, powerful sGRB seen off-axis. Detailed follow-up observations are thus essential before we can place stringent constraints on the nature of the relativistic ejecta in GW170817.

  15. Hydrodynamical simulations of the stream-core interaction in the slow merger of massive stars

    Science.gov (United States)

    Ivanova, N.; Podsiadlowski, Ph.; Spruit, H.

    2002-08-01

    We present detailed simulations of the interaction of a stream emanating from a mass-losing secondary with the core of a massive supergiant in the slow merger of two stars inside a common envelope. The dynamics of the stream can be divided into a ballistic phase, starting at the L1 point, and a hydrodynamical phase, where the stream interacts strongly with the core. Considering the merger of a 1- and 5-Msolar star with a 20-Msolar evolved supergiant, we present two-dimensional hydrodynamical simulations using the PROMETHEUS code to demonstrate how the penetration depth and post-impact conditions depend on the initial properties of the stream material (e.g. entropy, angular momentum, stream width) and the properties of the core (e.g. density structure and rotation rate). Using these results, we present a fitting formula for the entropy generated in the stream-core interaction and a recipe for the determination of the penetration depth based on a modified Bernoulli integral.

  16. Probing Minor-merger-driven Star Formation In Early-type Galaxies Using Spatially-resolved Spectro-photometric Studies

    Science.gov (United States)

    Kaviraj, Sugata; Crockett, M.; Silk, J.; O'Connell, R. W.; Whitmore, B.; Windhorst, R.; Cappellari, M.; Bureau, M.; Davies, R.

    2012-01-01

    Recent studies that leverage the rest-frame ultraviolet (UV) spectrum have revealed widespread recent star formation in early-type galaxies (ETGs), traditionally considered to be old, passively-evolving systems. This recent star formation builds 20% of the ETG stellar mass after z 1, driven by repeated minor mergers between ETGs and small, gas-rich satellites. We demonstrate how spatially-resolved studies, using a combination of high-resolution UV-optical imaging and integral-field spectroscopy (IFS), is a powerful tool to quantify the assembly history of individual ETGs and elucidate the poorly-understood minor-merger process. Using a combination of WFC3 UV-optical (2500-8200 angstroms) imaging and IFS from the SAURON project of the ETG NGC 4150, we show that this galaxy experienced a merger with mass ratio 1:15 around 0.9 Gyr ago, which formed 3% of its stellar mass and a young kinematically-decoupled core. A UV-optical analysis of its globular cluster system shows that the bulk of the stars locked up in these clusters likely formed 6-7 Gyrs in the past. We introduce a new HST-WFC3 programme, approved in Cycle 19, which will leverage similar UV-optical imaging of a representative sample of nearby ETGs from SAURON to study the recent star formation and its drivers in unprecedented detail and put definitive constraints on minor-merger-driven star formation in massive galaxies at late epochs.

  17. Dynamical ejecta from precessing neutron star-black hole mergers with a hot, nuclear-theory based equation of state

    International Nuclear Information System (INIS)

    Foucart, F; Kasen, D; Desai, D; Brege, W; Duez, M D; Hemberger, D A; Scheel, M A; Kidder, L E; Pfeiffer, H P

    2017-01-01

    Neutron star-black hole binaries are among the strongest sources of gravitational waves detectable by current observatories. They can also power bright electromagnetic signals (gamma-ray bursts, kilonovae), and may be a significant source of production of r-process nuclei. A misalignment of the black hole spin with respect to the orbital angular momentum leads to precession of that spin and of the orbital plane, and has a significant effect on the properties of the post-merger remnant and of the material ejected by the merger. We present a first set of simulations of precessing neutron star-black hole mergers using a hot, composition dependent, nuclear-theory based equation of state (DD2). We show that the mass of the remnant and of the dynamical ejecta are broadly consistent with the result of simulations using simpler equations of state, while differences arise when considering the dynamics of the merger and the velocity of the ejecta. We show that the latter can easily be understood from assumptions about the composition of low-density, cold material in the different equations of state, and propose an updated estimate for the ejecta velocity which takes those effects into account. We also present an updated mesh-refinement algorithm which allows us to improve the numerical resolution used to evolve neutron star-black hole mergers. (paper)

  18. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

    Science.gov (United States)

    Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G.; Doctor, Z.; Chornock, R.; Villar, V. A.; Cowperthwaite, P. S.; Annis, J.; Brout, D.; Brown, D. A.; Chen, H.-Y.; Eftekhari, T.; Frieman, J. A.; Holz, D. E.; Metzger, B. D.; Rest, A.; Sako, M.; Soares-Santos, M.

    2017-10-01

    We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational-wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at ≳ 10 {Gyr} ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 {M}⊙ yr-1, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of {11.2}-1.4+0.7 Gyr, with a 90% confidence range of 6.8{--}13.6 {Gyr}. This in turn indicates an initial binary separation of ≈ 4.5 {R}⊙ , comparable to the inferred values for Galactic BNS systems. We also use new and archival Hubble Space Telescope images to measure a projected offset of the optical counterpart of 2.1 kpc (0.64r e ) from the center of NGC 4993 and to place a limit of {M}r≳ -7.2 mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of ˜200 km s-1. Future GW-EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of r-process enrichment in the universe.

  19. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

    Energy Technology Data Exchange (ETDEWEB)

    Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G.; Doctor, Z.; Chornock, R.; Villar, V. A.; Cowperthwaite, P. S.; Annis, J.; Brout, D.; Brown, D. A.; Chen, H. -Y.; Eftekhari, T.; Frieman, J. A.; Holz, D. E.; Metzger, B. D.; Rest, A.; Sako, M.; Soares-Santos, M.

    2017-10-16

    We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at $\\gtrsim 10$ Gyr ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 M$_{\\odot}$ yr$^{-1}$, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of $11.2^{+0.7}_{-1.4}$ Gyr, with a 90% confidence range of $6.8-13.6$ Gyr. This in turn indicates an initial binary separation of $\\approx 4.5$ R$_{\\odot}$, comparable to the inferred values for Galactic BNS systems. We also use new and archival $Hubble$ $Space$ $Telescope$ images to measure a projected offset of the optical counterpart of $2.1$ kpc (0.64$r_{e}$) from the center of NGC 4993 and to place a limit of $M_{r} \\gtrsim -7.2$ mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of $\\sim 200$ km s$^{-1}$. Future GW$-$EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of $r$-process enrichment in the Universe.

  20. Illuminating gravitational waves: A concordant picture of photons from a neutron star merger.

    Science.gov (United States)

    Kasliwal, M M; Nakar, E; Singer, L P; Kaplan, D L; Cook, D O; Van Sistine, A; Lau, R M; Fremling, C; Gottlieb, O; Jencson, J E; Adams, S M; Feindt, U; Hotokezaka, K; Ghosh, S; Perley, D A; Yu, P-C; Piran, T; Allison, J R; Anupama, G C; Balasubramanian, A; Bannister, K W; Bally, J; Barnes, J; Barway, S; Bellm, E; Bhalerao, V; Bhattacharya, D; Blagorodnova, N; Bloom, J S; Brady, P R; Cannella, C; Chatterjee, D; Cenko, S B; Cobb, B E; Copperwheat, C; Corsi, A; De, K; Dobie, D; Emery, S W K; Evans, P A; Fox, O D; Frail, D A; Frohmaier, C; Goobar, A; Hallinan, G; Harrison, F; Helou, G; Hinderer, T; Ho, A Y Q; Horesh, A; Ip, W-H; Itoh, R; Kasen, D; Kim, H; Kuin, N P M; Kupfer, T; Lynch, C; Madsen, K; Mazzali, P A; Miller, A A; Mooley, K; Murphy, T; Ngeow, C-C; Nichols, D; Nissanke, S; Nugent, P; Ofek, E O; Qi, H; Quimby, R M; Rosswog, S; Rusu, F; Sadler, E M; Schmidt, P; Sollerman, J; Steele, I; Williamson, A R; Xu, Y; Yan, L; Yatsu, Y; Zhang, C; Zhao, W

    2017-12-22

    Merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) with gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. Instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. We posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet. Copyright © 2017, American Association for the Advancement of Science.

  1. Implications of Binary Black Hole Detections on the Merger Rates of Double Neutron Stars and Neutron Star–Black Holes

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Anuradha; Arun, K. G.; Sathyaprakash, B. S., E-mail: axg645@psu.edu, E-mail: kgarun@cmi.ac.in, E-mail: bss25@psu.edu [Institute for Gravitation and Cosmos, Physics Department, Pennsylvania State University, University Park, PA 16802 (United States)

    2017-11-01

    We show that the inferred merger rate and chirp masses of binary black holes (BBHs) detected by advanced LIGO (aLIGO) can be used to constrain the rate of double neutron star (DNS) and neutron star–black hole (NSBH) mergers in the universe. We explicitly demonstrate this by considering a set of publicly available population synthesis models of Dominik et al. and show that if all the BBH mergers, GW150914, LVT151012, GW151226, and GW170104, observed by aLIGO arise from isolated binary evolution, the predicted DNS merger rate may be constrained to be 2.3–471.0 Gpc{sup −3} yr{sup −1} and that of NSBH mergers will be constrained to 0.2–48.5 Gpc{sup −3} yr{sup −1}. The DNS merger rates are not constrained much, but the NSBH rates are tightened by a factor of ∼4 as compared to their previous rates. Note that these constrained DNS and NSBH rates are extremely model-dependent and are compared to the unconstrained values 2.3–472.5 Gpc{sup −3} yr{sup −1} and 0.2–218 Gpc{sup −3} yr{sup −1}, respectively, using the same models of Dominik et al. (2012a). These rate estimates may have implications for short Gamma Ray Burst progenitor models assuming they are powered (solely) by DNS or NSBH mergers. While these results are based on a set of open access population synthesis models, which may not necessarily be the representative ones, the proposed method is very general and can be applied to any number of models, thereby yielding more realistic constraints on the DNS and NSBH merger rates from the inferred BBH merger rate and chirp mass.

  2. A relationship of polycyclic aromatic hydrocarbon features with galaxy merger in star-forming galaxies at z < 0.2

    Science.gov (United States)

    Murata, Katsuhiro L.; Yamada, Rika; Oyabu, Shinki; Kaneda, Hidehiro; Ishihara, Daisuke; Yamagishi, Mitsuyoshi; Kokusho, Takuma; Takeuchi, Tsutomu T.

    2017-11-01

    Using the AKARI, Wide-field Infrared Survey Explorer (WISE), Infrared Astronomical Satellite (IRAS), Sloan Digital Sky Survey (SDSS) and Hubble Space Telescope (HST) data, we investigated the relation of polycyclic aromatic hydrocarbon (PAH) mass (MPAH), very small grain mass (MVSG), big grain mass (MBG) and stellar mass (Mstar) with galaxy merger for 55 star-forming galaxies at redshift z 0.1, we divided the galaxies into merger galaxies and non-merger galaxies with the morphological parameter asymmetry A, and quantified merging stages of galaxies based on the morphological indicators, the second-order momentum of the brightest 20 per cent region M20 and the Gini coefficient. We find that MPAH/MBG of merger galaxies tend to be lower than that of non-merger galaxies and there are no systematic differences of MVSG/MBG and MBG/Mstar between merger galaxies and non-merger galaxies. We find that galaxies with very low MPAH/MBG seem to be merger galaxies at late stages. These results suggest that PAHs are partly destroyed at late stages of merging processes. Furthermore, we investigated MPAH/MBG variations in radiation field intensity strength G0 and the emission line ratio of [O I] λ 6300/Hα that is a shock tracer for merger galaxies and find that MPAH/MBG decreases with increasing both G0 and [O I]/Hα. PAH destruction is likely to be caused by two processes: strong radiation fields and large-scale shocks during merging processes of galaxies.

  3. Implications of Binary Black Hole Detections on the Merger Rates of Double Neutron Stars and Neutron Star–Black Holes

    International Nuclear Information System (INIS)

    Gupta, Anuradha; Arun, K. G.; Sathyaprakash, B. S.

    2017-01-01

    We show that the inferred merger rate and chirp masses of binary black holes (BBHs) detected by advanced LIGO (aLIGO) can be used to constrain the rate of double neutron star (DNS) and neutron star–black hole (NSBH) mergers in the universe. We explicitly demonstrate this by considering a set of publicly available population synthesis models of Dominik et al. and show that if all the BBH mergers, GW150914, LVT151012, GW151226, and GW170104, observed by aLIGO arise from isolated binary evolution, the predicted DNS merger rate may be constrained to be 2.3–471.0 Gpc −3 yr −1 and that of NSBH mergers will be constrained to 0.2–48.5 Gpc −3 yr −1 . The DNS merger rates are not constrained much, but the NSBH rates are tightened by a factor of ∼4 as compared to their previous rates. Note that these constrained DNS and NSBH rates are extremely model-dependent and are compared to the unconstrained values 2.3–472.5 Gpc −3 yr −1 and 0.2–218 Gpc −3 yr −1 , respectively, using the same models of Dominik et al. (2012a). These rate estimates may have implications for short Gamma Ray Burst progenitor models assuming they are powered (solely) by DNS or NSBH mergers. While these results are based on a set of open access population synthesis models, which may not necessarily be the representative ones, the proposed method is very general and can be applied to any number of models, thereby yielding more realistic constraints on the DNS and NSBH merger rates from the inferred BBH merger rate and chirp mass.

  4. THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    De Mink, S. E. [Space Telescope Science Institute, Baltimore, MD (United States); Langer, N.; Izzard, R. G. [Argelander-Institut fuer Astronomie der Universitaet Bonn, D-53121 Bonn (Germany); Sana, H.; De Koter, A. [Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam (Netherlands)

    2013-02-20

    Rotation is thought to be a major factor in the evolution of massive stars-especially at low metallicity-with consequences for their chemical yields, ionizing flux, and final fate. Deriving the birth spin distribution is of high priority given its importance as a constraint on theories of massive star formation and as input for models of stellar populations in the local universe and at high redshift. Recently, it has become clear that the majority of massive stars interact with a binary companion before they die. We investigate how this affects the distribution of rotation rates, through stellar winds, expansion, tides, mass transfer, and mergers. For this purpose, we simulate a massive binary-star population typical for our Galaxy assuming continuous star formation. We find that, because of binary interaction, 20{sup +5} {sub -10}% of all massive main-sequence stars have projected rotational velocities in excess of 200 km s{sup -1}. We evaluate the effect of uncertain input distributions and physical processes and conclude that the main uncertainties are the mass transfer efficiency and the possible effect of magnetic braking, especially if magnetic fields are generated or amplified during mass accretion and stellar mergers. The fraction of rapid rotators we derive is similar to that observed. If indeed mass transfer and mergers are the main cause for rapid rotation in massive stars, little room remains for rapidly rotating stars that are born single. This implies that spin-down during star formation is even more efficient than previously thought. In addition, this raises questions about the interpretation of the surface abundances of rapidly rotating stars as evidence for rotational mixing. Furthermore, our results allow for the possibility that all early-type Be stars result from binary interactions and suggest that evidence for rotation in explosions, such as long gamma-ray bursts, points to a binary origin.

  5. The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers at z is approximately 1.5

    Science.gov (United States)

    Schmidt, Kasper B.; Rix, Hans-Walter; da Cunha, Elisabete; Brammer, Gabriel B.; Cox, Thomas J.; Van Dokkum, Pieter; Foerster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Jonsson, Patrik; hide

    2013-01-01

    We present an analysis of the spatial distribution of star formation in a sample of 60 visually identified galaxy merger candidates at z greater than 1. Our sample, drawn from the 3D-HST survey, is flux-limited and was selected to have high star formation rates based on fits of their broad-band, low spatial resolution spectral energy distributions. It includes plausible pre-merger (close pairs) and post-merger (single objects with tidal features) systems,with total stellar masses and star formation rates derived from multi-wavelength photometry. Here we use near-infrared slitless spectra from 3D-HST which produce H or [OIII] emission line maps as proxies for star-formation maps. This provides a first comprehensive high-resolution, empirical picture of where star formation occurred in galaxy mergers at the epoch of peak cosmic star formation rate. We find that detectable star formation can occur in one or both galaxy centres, or in tidal tails. The most common case (58%) is that star formation is largely concentrated in a single, compact region, coincident with the centre of (one of) the merger components. No correlations between star formation morphology and redshift, total stellar mass, or star formation rate are found. A restricted set of hydrodynamical merger simulationsbetween similarly massive and gas-rich objects implies that star formation should be detectable in both merger components, when the gas fractions of the individual components are the same. This suggests that z is approximately 1.5 mergers typically occur between galaxies whose gas fractions, masses, andor star formation rates are distinctly different from one another.

  6. Gravitational waves, neutrino emissions and effects of hyperons in binary neutron star mergers

    International Nuclear Information System (INIS)

    Kiuchi, Kenta; Sekiguchi, Yuichiro; Kyutoku, Koutarou; Shibata, Masaru

    2012-01-01

    Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that for the nucleonic and hyperonic EOS, a hyper-massive neutron star (HMNS) with a long lifetime (t life ≥ 10 ms) is the outcome for the total mass ≅2.7M sun . For the total mass ≅3 M sun , a long-lived (short-lived with t life ≅ 3 ms) HMNS is the outcome for the nucleonic (hyperonic) EOS. It is shown that the typical total neutrino luminosity of the HMNS is ∼3-6 x 10 53 erg s -1 and the effective amplitude of gravitational waves from the HMNS is 1-4 x 10 -22 at f ≅ 2-3.2 kHz for a source of distance of 100 Mpc. During the HMNS phase, characteristic frequencies of gravitational waves shift to a higher frequency for the hyperonic EOS in contrast to the nucleonic EOS in which they remain constant approximately. Our finding suggests that the effects of hyperons are well imprinted in gravitational waves and their detection will give us a potential opportunity to explore the composition of the neutron star matter. We present the neutrino luminosity curve when a black hole is formed as well. (paper)

  7. Probing Extreme-density Matter with Gravitational-wave Observations of Binary Neutron Star Merger Remnants

    Energy Technology Data Exchange (ETDEWEB)

    Radice, David [Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540 (United States); Bernuzzi, Sebastiano [Department of Mathematical, Physical and Computer Sciences, University of Parma, I-43124 Parma (Italy); Pozzo, Walter Del [Dipartimento di Fisica “Enrico Fermi,” Università di Pisa, Pisa I-56127 (Italy); Roberts, Luke F. [NSCL/FRIB and Department of Physics and Astronomy, Michigan State University, 640 S Shaw Lane, East Lansing, MI 48824 (United States); Ott, Christian D. [TAPIR, Walter Burke Institute for Theoretical Physics, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125 (United States)

    2017-06-20

    We present a proof-of-concept study, based on numerical-relativity simulations, of how gravitational waves (GWs) from neutron star merger remnants can probe the nature of matter at extreme densities. Phase transitions and extra degrees of freedom can emerge at densities beyond those reached during the inspiral, and typically result in a softening of the equation of state (EOS). We show that such physical effects change the qualitative dynamics of the remnant evolution, but they are not identifiable as a signature in the GW frequency, with the exception of possible black hole formation effects. The EOS softening is, instead, encoded in the GW luminosity and phase and is in principle detectable up to distances of the order of several megaparsecs with advanced detectors and up to hundreds of megaparsecs with third-generation detectors. Probing extreme-density matter will require going beyond the current paradigm and developing a more holistic strategy for modeling and analyzing postmerger GW signals.

  8. Probing Extreme-density Matter with Gravitational-wave Observations of Binary Neutron Star Merger Remnants

    International Nuclear Information System (INIS)

    Radice, David; Bernuzzi, Sebastiano; Pozzo, Walter Del; Roberts, Luke F.; Ott, Christian D.

    2017-01-01

    We present a proof-of-concept study, based on numerical-relativity simulations, of how gravitational waves (GWs) from neutron star merger remnants can probe the nature of matter at extreme densities. Phase transitions and extra degrees of freedom can emerge at densities beyond those reached during the inspiral, and typically result in a softening of the equation of state (EOS). We show that such physical effects change the qualitative dynamics of the remnant evolution, but they are not identifiable as a signature in the GW frequency, with the exception of possible black hole formation effects. The EOS softening is, instead, encoded in the GW luminosity and phase and is in principle detectable up to distances of the order of several megaparsecs with advanced detectors and up to hundreds of megaparsecs with third-generation detectors. Probing extreme-density matter will require going beyond the current paradigm and developing a more holistic strategy for modeling and analyzing postmerger GW signals.

  9. MASTER Optical Detection of the First LIGO/Virgo Neutron Star Binary Merger GW170817

    Science.gov (United States)

    Lipunov, V. M.; Gorbovskoy, E.; Kornilov, V. G.; . Tyurina, N.; Balanutsa, P.; Kuznetsov, A.; Vlasenko, D.; Kuvshinov, D.; Gorbunov, I.; Buckley, D. A. H.; Krylov, A. V.; Podesta, R.; Lopez, C.; Podesta, F.; Levato, H.; Saffe, C.; Mallamachi, C.; Potter, S.; Budnev, N. M.; Gress, O.; Ishmuhametova, Yu.; Vladimirov, V.; Zimnukhov, D.; Yurkov, V.; Sergienko, Yu.; Gabovich, A.; Rebolo, R.; Serra-Ricart, M.; Israelyan, G.; Chazov, V.; Wang, Xiaofeng; Tlatov, A.; Panchenko, M. I.

    2017-11-01

    Following the discovery of the gravitational-wave source GW170817 by three Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo antennae (Abbott et al., 2017a), the MASTER Global Robotic Net telescopes obtained the first image of the NGC 4993 host galaxy. An optical transient, MASTER OTJ130948.10-232253.3/SSS17a was later found, which appears to be a kilonova resulting from the merger of two neutron stars (NSs). Here we describe this independent detection and photometry of the kilonova made in white light, and in B, V, and R filters. We note that the luminosity of this kilonova in NGC 4993 is very close to those measured for other kilonovae possibly associated with gamma-ray burst (GRB) 130603 and GRB 080503.

  10. Galactic r-process enrichment by neutron star mergers in cosmological simulations of a Milky Way-mass galaxy

    Science.gov (United States)

    van de Voort, Freeke; Quataert, Eliot; Hopkins, Philip F.; Kereš, Dušan; Faucher-Giguère, Claude-André

    2015-02-01

    We quantify the stellar abundances of neutron-rich r-process nuclei in cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback In Realistic Environments project. The galaxy is enriched with r-process elements by binary neutron star (NS) mergers and with iron and other metals by supernovae. These calculations include key hydrodynamic mixing processes not present in standard semi-analytic chemical evolution models, such as galactic winds and hydrodynamic flows associated with structure formation. We explore a range of models for the rate and delay time of NS mergers, intended to roughly bracket the wide range of models consistent with current observational constraints. We show that NS mergers can produce [r-process/Fe] abundance ratios and scatter that appear reasonably consistent with observational constraints. At low metallicity, [Fe/H] ≲ -2, we predict there is a wide range of stellar r-process abundance ratios, with both supersolar and subsolar abundances. Low-metallicity stars or stars that are outliers in their r-process abundance ratios are, on average, formed at high redshift and located at large galactocentric radius. Because NS mergers are rare, our results are not fully converged with respect to resolution, particularly at low metallicity. However, the uncertain rate and delay time distribution of NS mergers introduce an uncertainty in the r-process abundances comparable to that due to finite numerical resolution. Overall, our results are consistent with NS mergers being the source of most of the r-process nuclei in the Universe.

  11. GRAVITATIONAL WAVES FROM MASSIVE MAGNETARS FORMED IN BINARY NEUTRON STAR MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    Dall' Osso, Simone [Theoretical Astrophysics, University of Tübingen, auf der Morgenstelle 10 D-72076 (Germany); Giacomazzo, Bruno [Physics Department, University of Trento, via Sommarive 14, I-38123 Trento (Italy); Perna, Rosalba [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Stella, Luigi, E-mail: simone.dallosso@uni-tuebingen.de [INAF-Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio Catone, Roma (Italy)

    2015-01-01

    Binary neutron star (NS) mergers are among the most promising sources of gravitational waves (GWs), as well as candidate progenitors for short gamma-ray bursts (SGRBs). Depending on the total initial mass of the system and the NS equation of state (EOS), the post-merger phase can be characterized by a prompt collapse to a black hole or by the formation of a supramassive NS, or even a stable NS. In the latter cases of post-merger NS (PMNS) formation, magnetic field amplification during the merger will produce a magnetar and induce a mass quadrupole moment in the newly formed NS. If the timescale for orthogonalization of the magnetic symmetry axis with the spin axis is smaller than the spindown time, the NS will radiate its spin down energy primarily via GWs. Here we study this scenario for the various outcomes of NS formation: we generalize the set of equilibrium states for a twisted torus magnetic configuration to include solutions that, for the same external dipolar field, carry a larger magnetic energy reservoir; we hence compute the magnetic ellipticity for such configurations, and the corresponding strength of the expected GW signal as a function of the relative magnitude of the dipolar and toroidal field components. The relative number of GW detections from PMNSs and from binary NSs is a very strong function of the NS EOS, being higher (∼1%) for the stiffest EOSs and negligibly small for the softest ones. For intermediate-stiffness EOSs, such as the n = 4/7 polytrope recently used by Giacomazzo and Perna or the GM1 used by Lasky et al., the relative fraction is ∼0.3%; correspondingly, we estimate a GW detection rate from stable PMNSs of ∼0.1-1 yr{sup –1} with advanced detectors, and of ∼100-1000 yr{sup –1} with detectors of third generation such as the Einstein Telescope. Measurement of such GW signals would provide constraints on the NS EOS and, in connection with an SGRB, on the nature of the binary progenitors giving rise to these events.

  12. Post-Newtonian Dynamics in Dense Star Clusters: Highly Eccentric, Highly Spinning, and Repeated Binary Black Hole Mergers.

    Science.gov (United States)

    Rodriguez, Carl L; Amaro-Seoane, Pau; Chatterjee, Sourav; Rasio, Frederic A

    2018-04-13

    We present models of realistic globular clusters with post-Newtonian dynamics for black holes. By modeling the relativistic accelerations and gravitational-wave emission in isolated binaries and during three- and four-body encounters, we find that nearly half of all binary black hole mergers occur inside the cluster, with about 10% of those mergers entering the LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead to the birth of a second generation of black holes with larger masses and high spins, which, depending on the black hole natal spins, can sometimes be retained in the cluster and merge again. As a result, globular clusters can produce merging binaries with detectable spins regardless of the birth spins of black holes formed from massive stars. These second-generation black holes would also populate any upper mass gap created by pair-instability supernovae.

  13. Post-Newtonian Dynamics in Dense Star Clusters: Highly Eccentric, Highly Spinning, and Repeated Binary Black Hole Mergers

    Science.gov (United States)

    Rodriguez, Carl L.; Amaro-Seoane, Pau; Chatterjee, Sourav; Rasio, Frederic A.

    2018-04-01

    We present models of realistic globular clusters with post-Newtonian dynamics for black holes. By modeling the relativistic accelerations and gravitational-wave emission in isolated binaries and during three- and four-body encounters, we find that nearly half of all binary black hole mergers occur inside the cluster, with about 10% of those mergers entering the LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead to the birth of a second generation of black holes with larger masses and high spins, which, depending on the black hole natal spins, can sometimes be retained in the cluster and merge again. As a result, globular clusters can produce merging binaries with detectable spins regardless of the birth spins of black holes formed from massive stars. These second-generation black holes would also populate any upper mass gap created by pair-instability supernovae.

  14. NECESSARY CONDITIONS FOR SHORT GAMMA-RAY BURST PRODUCTION IN BINARY NEUTRON STAR MERGERS

    International Nuclear Information System (INIS)

    Murguia-Berthier, Ariadna; Montes, Gabriela; Ramirez-Ruiz, Enrico; De Colle, Fabio; Lee, William H.

    2014-01-01

    The central engine of short gamma-ray bursts (sGRBs) is hidden from direct view, operating at a scale much smaller than that probed by the emitted radiation. Thus we must infer its origin not only with respect to the formation of the trigger—the actual astrophysical configuration that is capable of powering an sGRB—but also from the consequences that follow from the various evolutionary pathways that may be involved in producing it. Considering binary neutron star mergers we critically evaluate, analytically and through numerical simulations, whether the neutrino-driven wind produced by the newly formed hyper-massive neutron star can allow the collimated relativistic outflow that follows its collapse to actually produce an sGRB or not. Upon comparison with the observed sGRB duration distribution, we find that collapse cannot be significantly delayed (≤100 ms) before the outflow is choked, thus limiting the possibility that long-lived hyper-massive remnants can account for these events. In the case of successful breakthrough of the jet through the neutrino-driven wind, the energy stored in the cocoon could contribute to the precursor and extended emission observed in sGRBs

  15. Properties of Neutrino-driven Ejecta from the Remnant of a Binary Neutron Star Merger: Pure Radiation Hydrodynamics Case

    Energy Technology Data Exchange (ETDEWEB)

    Fujibayashi, Sho [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Sekiguchi, Yuichiro [Department of Physics, Toho University, Funabashi, Chiba 274-8510 (Japan); Kiuchi, Kenta; Shibata, Masaru, E-mail: sho.fujibayashi@yukawa.kyoto-u.ac.jp [Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2017-09-10

    We performed general relativistic, long-term, axisymmetric neutrino radiation hydrodynamics simulations for the remnant formed after a binary neutron star merger, which consists of a massive neutron star and a torus surrounding it. As an initial condition, we employ the result derived in a three-dimensional, numerical relativity simulation for the binary neutron star merger. We investigate the properties of neutrino-driven ejecta. Due to the pair-annihilation heating, the dynamics of the neutrino-driven ejecta are significantly modified. The kinetic energy of the ejecta is about two times larger than that in the absence of pair-annihilation heating. This suggests that the pair-annihilation heating plays an important role in the evolution of merger remnants. The relativistic outflow, which is required for driving gamma-ray bursts, is not observed because the specific heating rate around the rotational axis is not sufficiently high, due to the baryon loading caused by the neutrino-driven ejecta from the massive neutron star. We discuss the condition for launching the relativistic outflow and the nucleosynthesis in the ejecta.

  16. The electromagnetic Christodoulou memory effect and its application to neutron star binary mergers

    International Nuclear Information System (INIS)

    Bieri, Lydia; Chen, PoNing; Yau, Shing-Tung

    2012-01-01

    Gravitational waves are predicted by the general theory of relativity. It has been shown that gravitational waves have a nonlinear memory, displacing test masses permanently. This is called the Christodoulou memory. We proved that the electromagnetic field contributes at highest order to the nonlinear memory effect of gravitational waves, enlarging the permanent displacement of test masses. In experiments like LISA or LIGO which measure distances of test masses, the Christodoulou memory will manifest itself as a permanent displacement of these objects. It has been suggested to detect the Christodoulou memory effect using radio telescopes investigating small changes in pulsar’s pulse arrival times. The latter experiments are based on present-day technology and measure changes in frequency. In the present paper, we study the electromagnetic Christodoulou memory effect and compute it for binary neutron star mergers. These are typical sources of gravitational radiation. During these processes, not only mass and momenta are radiated away in form of gravitational waves, but also very strong magnetic fields are produced and radiated away. Moreover, a large portion of the energy is carried away by neutrinos. We give constraints on the conditions, where the energy transported by electromagnetic radiation is of similar or slightly higher order than the energy radiated in gravitational waves or in form of neutrinos. We find that for coalescing neutron stars, large magnetic fields magnify the Christodoulou memory as long as the gaseous environment is sufficiently rarefied. Thus the observed effect on test masses of a laser interferometer gravitational wave detector will be enlarged by the contribution of the electromagnetic field. Therefore, the present results are important for the planned experiments. Looking at the null asymptotics of spacetimes, which are solutions of the Einstein–Maxwell equations, we derive the electromagnetic Christodoulou memory effect. We obtain

  17. Neutron star mergers as a probe of modifications of general relativity with finite-range scalar forces

    Science.gov (United States)

    Sagunski, Laura; Zhang, Jun; Johnson, Matthew C.; Lehner, Luis; Sakellariadou, Mairi; Liebling, Steven L.; Palenzuela, Carlos; Neilsen, David

    2018-03-01

    Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test general relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universally coupled massive scalar field. Such scalar degrees of freedom (d.o.f.) are a characteristic feature of many extensions of general relativity. For concreteness, we work in the context of metric f (R ) gravity, which is equivalent to general relativity and a universally coupled scalar field with a nonlinear potential whose form is fixed by the choice of f (R ). In theories where neutron stars (or other compact objects) obtain a significant scalar charge, the resulting attractive finite-range scalar force has implications for both the inspiral and merger phases of binary systems. We first present an analysis of the inspiral dynamics in Newtonian limit, and forecast the constraints on the mass of the scalar and charge of the compact objects for the Advanced LIGO gravitational wave observatory. We then perform a comparative study of binary neutron star mergers in general relativity with those of a one-parameter model of f (R ) gravity using fully relativistic hydrodynamical simulations. These simulations elucidate the effects of the scalar on the merger and postmerger dynamics. We comment on the utility of the full waveform (inspiral, merger, postmerger) to probe different regions of parameter space for both the particular model of f (R ) gravity studied here and for finite-range scalar forces more generally.

  18. Shock Acceleration of Electrons and Synchrotron Emission from the Dynamical Ejecta of Neutron Star Mergers

    Science.gov (United States)

    Lee, Shiu-Hang; Maeda, Keiichi; Kawanaka, Norita

    2018-05-01

    Neutron star mergers (NSMs) eject energetic subrelativistic dynamical ejecta into circumbinary media. Analogous to supernovae and supernova remnants, the NSM dynamical ejecta are expected to produce nonthermal emission by electrons accelerated at a shock wave. In this paper, we present the expected radio and X-ray signals by this mechanism, taking into account nonlinear diffusive shock acceleration (DSA) and magnetic field amplification. We suggest that the NSM is unique as a DSA site, where the seed relativistic electrons are abundantly provided by the decays of r-process elements. The signal is predicted to peak at a few 100–1000 days after the merger, determined by the balance between the decrease of the number of seed electrons and the increase of the dissipated kinetic energy, due to the shock expansion. While the resulting flux can ideally reach the maximum flux expected from near-equipartition, the available kinetic energy dissipation rate of the NSM ejecta limits the detectability of such a signal. It is likely that the radio and X-ray emission are overwhelmed by other mechanisms (e.g., an off-axis jet) for an observer placed in a jet direction (i.e., for GW170817). However, for an off-axis observer, to be discovered once a number of NSMs are identified, the dynamical ejecta component is predicted to dominate the nonthermal emission. While the detection of this signal is challenging even with near-future facilities, this potentially provides a robust probe of the creation of r-process elements in NSMs.

  19. Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers

    Science.gov (United States)

    Siegel, Daniel M.; Metzger, Brian D.

    2018-05-01

    Merging binaries consisting of two neutron stars (NSs) or an NS and a stellar-mass black hole typically form a massive accretion torus around the remnant black hole or long-lived NS. Outflows from these neutrino-cooled accretion disks represent an important site for r-process nucleosynthesis and the generation of kilonovae. We present the first three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulations including weak interactions and a realistic equation of state of such accretion disks over viscous timescales (380 ms). We witness the emergence of steady-state MHD turbulence, a magnetic dynamo with an ∼20 ms cycle, and the generation of a “hot” disk corona that launches powerful thermal outflows aided by the energy released as free nucleons recombine into α-particles. We identify a self-regulation mechanism that keeps the midplane electron fraction low (Y e ∼ 0.1) over viscous timescales. This neutron-rich reservoir, in turn, feeds outflows that retain a sufficiently low value of Y e ≈ 0.2 to robustly synthesize third-peak r-process elements. The quasi-spherical outflows are projected to unbind 40% of the initial disk mass with typical asymptotic escape velocities of 0.1c and may thus represent the dominant mass ejection mechanism in NS–NS mergers. Including neutrino absorption, our findings agree with previous hydrodynamical α-disk simulations that the entire range of r-process nuclei from the first to the third r-process peak can be synthesized in the outflows, in good agreement with observed solar system abundances. The asymptotic escape velocities and quantity of ejecta, when extrapolated to moderately higher disk masses, are consistent with those needed to explain the red kilonova emission following the NS merger GW170817.

  20. Neutron-Star Radius from a Population of Binary Neutron Star Mergers.

    Science.gov (United States)

    Bose, Sukanta; Chakravarti, Kabir; Rezzolla, Luciano; Sathyaprakash, B S; Takami, Kentaro

    2018-01-19

    We show how gravitational-wave observations with advanced detectors of tens to several tens of neutron-star binaries can measure the neutron-star radius with an accuracy of several to a few percent, for mass and spatial distributions that are realistic, and with none of the sources located within 100 Mpc. We achieve such an accuracy by combining measurements of the total mass from the inspiral phase with those of the compactness from the postmerger oscillation frequencies. For estimating the measurement errors of these frequencies, we utilize analytical fits to postmerger numerical relativity waveforms in the time domain, obtained here for the first time, for four nuclear-physics equations of state and a couple of values for the mass. We further exploit quasiuniversal relations to derive errors in compactness from those frequencies. Measuring the average radius to well within 10% is possible for a sample of 100 binaries distributed uniformly in volume between 100 and 300 Mpc, so long as the equation of state is not too soft or the binaries are not too heavy. We also give error estimates for the Einstein Telescope.

  1. LFsGRB: Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

    Science.gov (United States)

    Paul, Debdutta

    2018-04-01

    LFsGRB models the luminosity function (LF) of short Gamma Ray Bursts (sGRBs) by using the available catalog data of all short GRBs (sGRBs) detected till 2017 October, estimating the luminosities via pseudo-redshifts obtained from the Yonetoku correlation, and then assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. The data are fit well both by exponential cutoff powerlaw and broken powerlaw models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of short GRBs is derived. Assuming a short GRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present and future configurations of the GW detector networks.

  2. An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers

    Science.gov (United States)

    van de Voort, Freeke; Davis, Timothy A.; Matsushita, Satoki; Rowlands, Kate; Shabala, Stanislav S.; Allison, James R.; Ting, Yuan-Sen; Sansom, Anne E.; van der Werf, Paul P.

    2018-05-01

    Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt-Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density.

  3. Evolution models of helium white dwarf--main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    OpenAIRE

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2017-01-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with ...

  4. NEUTRON-STAR MERGER EJECTA AS OBSTACLES TO NEUTRINO-POWERED JETS OF GAMMA-RAY BURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Just, O.; Janka, H.-T.; Schwarz, N. [Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); Obergaulinger, M. [Departament d´Astronomia i Astrofísica, Universitat de València, Edifici d´Investigació Jeroni Muñoz, C/ Dr. Moliner, 50, E-46100 Burjassot (València) (Spain); Bauswein, A., E-mail: ojust@mpa-garching.mpg.de, E-mail: thj@mpa-garching.mpg.de [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece)

    2016-01-10

    We present the first special relativistic, axisymmetric hydrodynamic simulations of black hole-torus systems (approximating general relativistic gravity) as remnants of binary-neutron star (NS–NS) and neutron star–black hole (NS–BH) mergers, in which the viscously driven evolution of the accretion torus is followed with self-consistent energy-dependent neutrino transport and the interaction with the cloud of dynamical ejecta expelled during the NS–NS merging is taken into account. The modeled torus masses, BH masses and spins, and the ejecta masses, velocities, and spatial distributions are adopted from relativistic merger simulations. We find that energy deposition by neutrino annihilation can accelerate outflows with initially high Lorentz factors along polar low-density funnels, but only in mergers with extremely low baryon pollution in the polar regions. NS–BH mergers, where polar mass ejection during the merging phase is absent, provide sufficiently baryon-poor environments to enable neutrino-powered, ultrarelativistic jets with terminal Lorentz factors above 100 and considerable dynamical collimation, favoring short gamma-ray bursts (sGRBs), although their typical energies and durations might be too small to explain the majority of events. In the case of NS–NS mergers, however, neutrino emission of the accreting and viscously spreading torus is too short and too weak to yield enough energy for the outflows to break out from the surrounding ejecta shell as highly relativistic jets. We conclude that neutrino annihilation alone cannot power sGRBs from NS–NS mergers.

  5. NEUTRON-STAR MERGER EJECTA AS OBSTACLES TO NEUTRINO-POWERED JETS OF GAMMA-RAY BURSTS

    International Nuclear Information System (INIS)

    Just, O.; Janka, H.-T.; Schwarz, N.; Obergaulinger, M.; Bauswein, A.

    2016-01-01

    We present the first special relativistic, axisymmetric hydrodynamic simulations of black hole-torus systems (approximating general relativistic gravity) as remnants of binary-neutron star (NS–NS) and neutron star–black hole (NS–BH) mergers, in which the viscously driven evolution of the accretion torus is followed with self-consistent energy-dependent neutrino transport and the interaction with the cloud of dynamical ejecta expelled during the NS–NS merging is taken into account. The modeled torus masses, BH masses and spins, and the ejecta masses, velocities, and spatial distributions are adopted from relativistic merger simulations. We find that energy deposition by neutrino annihilation can accelerate outflows with initially high Lorentz factors along polar low-density funnels, but only in mergers with extremely low baryon pollution in the polar regions. NS–BH mergers, where polar mass ejection during the merging phase is absent, provide sufficiently baryon-poor environments to enable neutrino-powered, ultrarelativistic jets with terminal Lorentz factors above 100 and considerable dynamical collimation, favoring short gamma-ray bursts (sGRBs), although their typical energies and durations might be too small to explain the majority of events. In the case of NS–NS mergers, however, neutrino emission of the accreting and viscously spreading torus is too short and too weak to yield enough energy for the outflows to break out from the surrounding ejecta shell as highly relativistic jets. We conclude that neutrino annihilation alone cannot power sGRBs from NS–NS mergers

  6. NGC 2782: A Merger Remnant with Young Stars in its Gaseous Tidal Tail

    Science.gov (United States)

    Torres-Flores, S.; de Oliveira, C. Mendes; de Mello, D. F.; Scarano, S. Jr.; Urrutia-Viscarra, R.

    2012-01-01

    We have searched for young star-forming regions around the merger remnant NGC 2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources, located at distances greater than 26 kpc from the center of NGG 2782, and coinciding with its western HI tidal tail. These regions were resolved in several smaller systems when Gemini/GMOS r-band images were used. We compared the observed colors to stellar population synthesis models and we found that these objects have ages of l to ll11yr and masses ranging from 10(exp 3.9) to l0(exp 4.6) Solar Mass. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H)=8.74+/-0.20, 8.81+/-0.20 and 8.78+/-0.20). These metallicities are similar to the value presented by the nuclear region of NGG 2782 and also similar to the value presented for an object located close to the main body of NGG 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGG 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the center of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.

  7. MONTE CARLO NEUTRINO TRANSPORT THROUGH REMNANT DISKS FROM NEUTRON STAR MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    Richers, Sherwood; Ott, Christian D. [TAPIR, Mailcode 350-17, Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, CA 91125 (United States); Kasen, Daniel; Fernández, Rodrigo [Department of Astronomy and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States); O’Connor, Evan [Department of Physics, Campus Code 8202, North Carolina State University, Raleigh, NC 27695 (United States)

    2015-11-01

    We present Sedonu, a new open source, steady-state, special relativistic Monte Carlo (MC) neutrino transport code, available at bitbucket.org/srichers/sedonu. The code calculates the energy- and angle-dependent neutrino distribution function on fluid backgrounds of any number of spatial dimensions, calculates the rates of change of fluid internal energy and electron fraction, and solves for the equilibrium fluid temperature and electron fraction. We apply this method to snapshots from two-dimensional simulations of accretion disks left behind by binary neutron star mergers, varying the input physics and comparing to the results obtained with a leakage scheme for the cases of a central black hole and a central hypermassive neutron star. Neutrinos are guided away from the densest regions of the disk and escape preferentially around 45° from the equatorial plane. Neutrino heating is strengthened by MC transport a few scale heights above the disk midplane near the innermost stable circular orbit, potentially leading to a stronger neutrino-driven wind. Neutrino cooling in the dense midplane of the disk is stronger when using MC transport, leading to a globally higher cooling rate by a factor of a few and a larger leptonization rate by an order of magnitude. We calculate neutrino pair annihilation rates and estimate that an energy of 2.8 × 10{sup 46} erg is deposited within 45° of the symmetry axis over 300 ms when a central BH is present. Similarly, 1.9 × 10{sup 48} erg is deposited over 3 s when an HMNS sits at the center, but neither estimate is likely to be sufficient to drive a gamma-ray burst jet.

  8. MONTE CARLO NEUTRINO TRANSPORT THROUGH REMNANT DISKS FROM NEUTRON STAR MERGERS

    International Nuclear Information System (INIS)

    Richers, Sherwood; Ott, Christian D.; Kasen, Daniel; Fernández, Rodrigo; O’Connor, Evan

    2015-01-01

    We present Sedonu, a new open source, steady-state, special relativistic Monte Carlo (MC) neutrino transport code, available at bitbucket.org/srichers/sedonu. The code calculates the energy- and angle-dependent neutrino distribution function on fluid backgrounds of any number of spatial dimensions, calculates the rates of change of fluid internal energy and electron fraction, and solves for the equilibrium fluid temperature and electron fraction. We apply this method to snapshots from two-dimensional simulations of accretion disks left behind by binary neutron star mergers, varying the input physics and comparing to the results obtained with a leakage scheme for the cases of a central black hole and a central hypermassive neutron star. Neutrinos are guided away from the densest regions of the disk and escape preferentially around 45° from the equatorial plane. Neutrino heating is strengthened by MC transport a few scale heights above the disk midplane near the innermost stable circular orbit, potentially leading to a stronger neutrino-driven wind. Neutrino cooling in the dense midplane of the disk is stronger when using MC transport, leading to a globally higher cooling rate by a factor of a few and a larger leptonization rate by an order of magnitude. We calculate neutrino pair annihilation rates and estimate that an energy of 2.8 × 10 46 erg is deposited within 45° of the symmetry axis over 300 ms when a central BH is present. Similarly, 1.9 × 10 48 erg is deposited over 3 s when an HMNS sits at the center, but neither estimate is likely to be sufficient to drive a gamma-ray burst jet

  9. The rise and fall of stellar across the peak of cosmic star formation history: effects of mergers versus diffuse stellar mass acquisition

    Science.gov (United States)

    Welker, C.; Dubois, Y.; Devriendt, J.; Pichon, C.; Kaviraj, S.; Peirani, S.

    2017-02-01

    Building galaxy merger trees from a state-of-the-art cosmological hydrodynamical simulation, Horizon-AGN, we perform a statistical study of how mergers and diffuse stellar mass acquisition processes drive galaxy morphologic properties above z > 1. By diffuse mass acquisition here, we mean both accretion of stars by unresolved mergers (relative stellar mass growth smaller than 4.5 per cent) as well as in situ star formation when no resolved mergers are detected along the main progenitor branch of a galaxy. We investigate how stellar densities, galaxy sizes and galaxy morphologies (defined via shape parameters derived from the inertia tensor of the stellar density) depend on mergers of different mass ratios. We investigate how stellar densities, effective radii and shape parameters derived from the inertia tensor depend on mergers of different mass ratios. We find strong evidence that diffuse stellar accretion and in situ formation tend to flatten small galaxies over cosmic time, leading to the formation of discs. On the other hand, mergers, and not only the major ones, exhibit a propensity to puff up and destroy stellar discs, confirming the origin of elliptical galaxies. We confirm that mergers grow galaxy sizes more efficiently than diffuse processes (r_{0.5}∝ M_s^{0.85} and r_{0.5}∝ M_s^{0.1} on average, respectively) and we also find that elliptical galaxies are more susceptible to grow in size through mergers than disc galaxies with a size-mass evolution r_{0.5}∝ M_s^{1.2} instead of r_{0.5}∝ M_s^{-0.5}-M^{0.5} for discs depending on the merger mass ratio. The gas content drives the size-mass evolution due to merger with a faster size growth for gas-poor galaxies r_{0.5}∝ M_s2 than for gas-rich galaxies r0.5 ∝ Ms.

  10. Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers

    Science.gov (United States)

    Wu, Meng-Ru; Fernández, Rodrigo; Martínez-Pinedo, Gabriel; Metzger, Brian D.

    2016-12-01

    We consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star-black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important - and in some cases dominant - contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second r-process peak (mass number A ˜ 130), independent of model parameters, with significant production of A spike at A = 132 that is absent in the Solar system r-process distribution. The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. We conclude that disc outflows provide an important - and perhaps dominant - contribution to the r-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of r-process elements in the Galaxy.

  11. Central-engine-powered Bright X-Ray Flares in Short Gamma-Ray Bursts: A Hint of a Black Hole–Neutron Star Merger?

    Science.gov (United States)

    Mu, Hui-Jun; Gu, Wei-Min; Mao, Jirong; Hou, Shu-Jin; Lin, Da-Bin; Liu, Tong

    2018-05-01

    Short gamma-ray bursts may originate from the merger of a double neutron star (NS) or the merger of a black hole (BH) and an NS. We propose that the bright X-ray flare related to the central engine reactivity may indicate a BH–NS merger, since such a merger can provide more fallback materials and therefore a more massive accretion disk than the NS–NS merger. Based on the 49 observed short bursts with the Swift/X-ray Telescope follow-up observations, we find that three bursts have bright X-ray flares, among which three flares from two bursts are probably related to the central engine reactivity. We argue that these two bursts may originate from the BH–NS merger rather than the NS–NS merger. Our suggested link between the central-engine-powered bright X-ray flare and the BH–NS merger event can be checked by future gravitational wave detections from advanced LIGO and Virgo.

  12. Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event.

    Science.gov (United States)

    Kasen, Daniel; Metzger, Brian; Barnes, Jennifer; Quataert, Eliot; Ramirez-Ruiz, Enrico

    2017-11-02

    The cosmic origin of elements heavier than iron has long been uncertain. Theoretical modelling shows that the matter that is expelled in the violent merger of two neutron stars can assemble into heavy elements such as gold and platinum in a process known as rapid neutron capture (r-process) nucleosynthesis. The radioactive decay of isotopes of the heavy elements is predicted to power a distinctive thermal glow (a 'kilonova'). The discovery of an electromagnetic counterpart to the gravitational-wave source GW170817 represents the first opportunity to detect and scrutinize a sample of freshly synthesized r-process elements. Here we report models that predict the electromagnetic emission of kilonovae in detail and enable the mass, velocity and composition of ejecta to be derived from observations. We compare the models to the optical and infrared radiation associated with the GW170817 event to argue that the observed source is a kilonova. We infer the presence of two distinct components of ejecta, one composed primarily of light (atomic mass number less than 140) and one of heavy (atomic mass number greater than 140) r-process elements. The ejected mass and a merger rate inferred from GW170817 imply that such mergers are a dominant mode of r-process production in the Universe.

  13. Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    Science.gov (United States)

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2018-02-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

  14. THE FAST-ROTATING, LOW-GRAVITY SUBDWARF B STAR EC 22081-1916: REMNANT OF A COMMON ENVELOPE MERGER EVENT

    International Nuclear Information System (INIS)

    Geier, S.; Classen, L.; Heber, U.

    2011-01-01

    Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red-giant branch. In binary systems, mass transfer to the companion provides the extraordinary mass loss required for their formation. However, apparently single sdBs exist as well and their formation has been unclear for decades. The merger of helium white dwarfs (He-WDs) leading to an ignition of core helium burning or the merger of a helium core and a low-mass star during the common envelope phase have been proposed as processes leading to sdB formation. Here we report the discovery of EC 22081-1916 as a fast-rotating, single sdB star of low gravity. Its atmospheric parameters indicate that the hydrogen envelope must be unusually thick, which is at variance with the He-WD merger scenario, but consistent with a common envelope merger of a low-mass, possibly substellar object with a red-giant core.

  15. Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory

    NARCIS (Netherlands)

    Albert, A.; Andre, M.; Anghinolfi, M.; Ardid, M.; Aubert, J. -J.; Aublin, J.; Avgitas, T.; Baret, B.; Barrios-Marti, J.; Basa, S.; Belhorma, B.; Bertin, V.; Biagi, S.; Bormuth, R.; Bourret, S.; Bouwhuis, M. C.; Branzas, H.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Celli, S.; El Moursli, R. Cherkaoui; Chiarusi, T.; Circella, M.; Coelho, J. A. B.; Coleiro, A.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; Diaz, A. F.; Deschamps, A.; De Bonis, G.; Distefano, C.; Di Palma, I.; Domi, A.; Donzaud, C.; Dornic, D.; Drouhin, D.; Eberl, T.; El Bojaddaini, I.; El Khayati, N.; Elsaesser, D.; Enzenhofer, A.; Ettahiri, A.; Fassi, F.; Felis, I.; Fusco, L. A.; Gay, P.; Giordano, V.; Glotin, H.; Gregoire, T.; Ruiz, R. Gracia; Graf, K.; Hallmann, S.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernandez-Rey, J. J.; Hoessl, J.; Hofestaedt, J.; Illuminati, G.; James, C. W.; de Jong, M.; Jongen, M.; Kadler, M.; Kalekin, O.; Katz, U.; Kiessling, D.; Kouchner, A.; Kreter, M.; Kreykenbohm, I.; Kulikovskiy, V.; Lachaud, C.; Lahmann, R.; Lefevre, D.; Leonora, E.; Lotze, M.; Loucatos, S.; Marcelin, M.; Margiotta, A.; Marinelli, A.; Martinez-Mora, J. A.; Mele, R.; Melis, K.; Michael, T.; Migliozzi, P.; Moussa, A.; Navas, S.; Nezri, E.; Organokov, M.; Pavalas, G. E.; Pellegrino, C.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Quinn, L.; Racca, C.; Riccobene, G.; Sanchez-Losa, A.; Saldana, M.; Salvadori, I.; Samtleben, D. F. E.; Sanguineti, M.; Sapienza, P.; Schussler, F.; Sieger, C.; Spurio, M.; Stolarczyk, Th.; Taiuti, M.; Tayalati, Y.; Trovato, A.; Turpin, D.; Tonnis, C.; Vallage, B.; Van Elewyck, V.; Versari, F.; Vivolo, D.; Vizzoca, A.; Wilms, J.; Zornoza, J. D.; Zuniga, J.; Aartsen, M. G.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Al Samarai, I.; Altmann, D.; Andeen, K.; Anderson, T.; Ansseau, I.; Anton, G.; Arguelles, C.; Auffenberg, J.; Axani, S.; Bagherpour, H.; Bai, X.; Barron, J. P.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Tjus, J. Becker; Becker, K. H.; BenZvi, S.; Berley, D.; Bernardini, E.; Besson, D. Z.; Binder, G.; Bindig, D.; Blaufuss, E.; Blot, S.; Bohm, C.; Boerner, M.; Bos, F.; Bose, D.; Boeser, S.; Botner, O.; Bourbeau, E.; Bourbeau, J.; Bradascio, F.; Braun, J.; Brayeur, L.; Brenzke, M.; Bretz, H. -P.; Bron, S.; Brostean-Kaiser, J.; Burgman, A.; Carver, T.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Coenders, S.; Collin, G. H.; Conrad, J. M.; Cowen, D. F.; Cross, R.; Day, M.; de Andre, J. P. A. M.; De Clercq, C.; DeLaunay, J. J.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Diaz-Velez, J. C.; di Lorenzo, V.; Dujmovic, H.; Dumm, J. 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L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Gretarsson, E. M.; Groot, P.; Grote, H.; Grunewald, S.; Gruning, P.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Halim, O.; Hall, B. R.; Hall, E. D.; Hamilton, E. Z.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hannuksela, O. A.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Haster, C. -J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hinderer, T.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Horst, C.; Hough, J.; Houston, E. A.; Howell, E. J.; Hreibi, A.; Hu, Y. M.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Inta, R.; Intini, G.; Isa, H. N.; Isac, J. -M.; Isi, M.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jimenez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Junker, J.; Kalaghatgi, C. V.; Kalogera, V.; Kamai, B.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katolik, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kawabe, K.; Kefelian, F.; Keitel, D.; Kemball, A. J.; Kennedy, R.; Kent, C.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J. C.; Kim, K.; Kim, W.; Kim, W. S.; Kim, Y. -M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kinley-Hanlon, M.; Kirchhoff, R.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Knowles, T. D.; Koch, P.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kramer, C.; Kringel, V.; Krishnan, B.; Krolak, A.; Kuehn, G.; Kumar, P.; Kumar, R.; Kumar, S.; Kuo, L.; Kutynia, A.; Kwang, S.; Lackey, B. D.; Lai, K. H.; Landry, M.; Lang, R. N.; Lange, J.; Lantz, B.; Lanza, R. K.; Lartaux-Vollard, A.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lee, C. H.; Lee, H. M.; Lee, H. W.; Lee, K.; Lehmann, J.; Lenon, A.; Leonardi, M.; Leroy, N.; Letendre, N.; Levin, Y.; Li, T. G. F.; Linker, S. D.; Littenberg, T. B.; Liu, J.; Lo, R. K. L.; Lockerbie, N. A.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lousto, C. O.; Lovelace, G.; Lueck, H.; Lumaca, D.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macas, R.; Macfoy, S.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Hernandez, I. Magana; Magana-Sandoval, F.; Zertuche, L. Magana; Magee, R. M.; Majorana, E.; Maksimovic, I.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marka, S.; Marka, Z.; Markakis, C.; Markosyan, A. S.; Markowitz, A.; Maros, E.; Marquina, A.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Mason, K.; Massera, E.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matas, A.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McCuller, L.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McNeill, L.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Mejuto-Villa, E.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, B. B.; Miller, J.; Millhouse, M.; Milovich-Goff, M. C.; Minazzoli, O.; Minenkov, Y.; Ming, J.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moffa, D.; Moggi, A.; Mogushi, K.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Muniz, E. A.; Muratore, M.; Murray, P. G.; Napier, K.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Neilson, J.; Nelemans, G.; Nelson, T. J. N.; Nery, M.; Neunzert, A.; Nevin, L.; Newport, J. M.; Newton, G.; Ng, K. K. Y.; Nguyen, T. T.; Nichols, D.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Noack, A.; Nocera, F.; Nolting, D.; North, C.; Nuttall, L. K.; Oberling, J.; O'Dea, G. D.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Okada, M. A.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; Ormiston, R.; Ortega, L. F.; O'Shaughnessy, R.; Ossokine, S.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pace, A. E.; Page, J.; Page, M. A.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, Howard; Pan, Huang-Wei; Pang, B.; Pang, P. T. H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Parida, A.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patil, M.; Patricelli, B.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perez, C. J.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pirello, M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Porter, E. K.; Post, A.; Powell, J.; Prasad, J.; Pratt, J. W. W.; Pratten, G.; Predoi, V.; Prestegard, T.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L. G.; Puncken, O.; Punturo, M.; Puppo, P.; Puerrer, M.; Qi, H.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rajbhandari, B.; Rakhmanov, M.; Ramirez, K. E.; Ramos-Buades, A.; Rapagnani, P.; Raymond, V.; Razzano, M.; Read, J.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Ren, W.; Reyes, S. D.; Ricci, F.; Ricker, P. M.; Rieger, S.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romel, C. L.; Romie, J. H.; Rosinska, D.; Ross, M. P.; Rowan, S.; Ruediger, A.; Ruggi, P.; Rutins, G.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sampson, L. M.; Sanchez, E. J.; Sanchez, L. E.; Sanchis-Gual, N.; Sandberg, V.; Sanders, J. R.; Sassolas, B.; Saulson, P. R.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Scheel, M.; Scheuer, J.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schoenbeck, A.; Schreiber, E.; Schuette, D.; Schulte, B. W.; Schutz, B. F.; Schwalbe, S. G.; Scott, J.; Scott, S. M.; Seidel, E.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Shaddock, D. A.; Shaffer, T. J.; Shah, A. A.; Shahriar, M. S.; Shaner, M. B.; Shao, L.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, L. P.; Singh, A.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, B.; Smith, R. J. E.; Smith, R. J. E.; Somala, S.; Son, E. J.; Sonnenberg, J. A.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Spencer, A. P.; Srivastava, A. K.; Staats, K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stevenson, S. P.; Stone, R.; Stops, D. J.; Strain, K. A.; Stratta, G.; Strigin, S. E.; Strunk, A.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Suresh, J.; Sutton, P. J.; Swinkels, B. L.; Szczepanczyk, M. J.; Tacca, M.; Tait, S. C.; Talbot, C.; Talukder, D.; Tanner, D. B.; Tapai, M.; Taracchini, A.; Tasson, J. D.; Taylor, J. A.; Taylor, R.; Tewari, S. V.; Theeg, T.; Thies, F.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tonelli, M.; Tornasi, Z.; Torres-Forne, A.; Torrie, C. I.; Toyra, D.; Travasso, F.; Traylor, G.; Trinastic, J.; Tringali, M. C.; Trozzo, L.; Tsang, K. W.; Tse, M.; Tso, R.; Tsukada, L.; Tsuna, D.; Tuyenbayev, D.; Ueno, K.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Varma, V.; Vass, S.; Vasuth, M.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Venugopalan, G.; Verkindt, D.; Vetrano, F.; Vicere, A.; Viets, A. D.; Vinciguerra, S.; Vine, D. J.; Vinet, J. -Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walet, R.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, J. Z.; Wang, W. H.; Wang, Y. F.; Ward, R. L.; Warner, J.; Was, M.; Watchi, J.; Weaver, B.; Wei, L. -W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wessel, E. K.; Wessels, P.; Westerweck, J.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Whittle, C.; Wilken, D.; Williams, D.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Wofford, J.; Wong, K. W. K.; Worden, J.; Wright, J. L.; Wu, D. S.; Wysocki, D. M.; Xiao, S.; Yamamoto, H.; Yancey, C. C.; Yang, L.; Yap, M. J.; Yazback, M.; Yu, Hang; Yu, Haocun; Yvert, M.; Zadrozny, A.; Zanolin, M.; Zelenova, T.; Zendri, J. -P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, T.; Zhang, Y. -H.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, S. J.; Zhu, X. J.; Zucker, M. E.; Zweizig, J.

    2017-01-01

    The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield

  16. A peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor.

    Science.gov (United States)

    Zhang, B-B; Zhang, B; Sun, H; Lei, W-H; Gao, H; Li, Y; Shao, L; Zhao, Y; Hu, Y-D; Lü, H-J; Wu, X-F; Fan, X-L; Wang, G; Castro-Tirado, A J; Zhang, S; Yu, B-Y; Cao, Y-Y; Liang, E-W

    2018-01-31

    Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASA's Fermi Space Telescope as GRB 170817A. Here, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least [Formula: see text] Gpc -3  yr -1 , which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the Fermi archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs.

  17. HERSCHEL OBSERVATIONS OF MAJOR MERGER PAIRS AT z = 0: DUST MASS AND STAR FORMATION

    International Nuclear Information System (INIS)

    Cao, Chen; Xu, Cong Kevin; Lu, Nanyao; Mazzarella, Joe; Domingue, Donovan; Ronca, Joseph; Jacques, Allison; Buat, Veronique; Cheng, Yi-Wen; Gao, Yu; Huang, Jiasheng; Jarrett, Thomas H.; Lisenfeld, Ute; Sun, Wei-Hsin; Wu, Hong; Yun, Min S.

    2016-01-01

    We present Herschel PACS and SPIRE far-infrared (FIR) and submillimeter imaging observations for a large K-band selected sample of 88 close major-merger pairs of galaxies (H-KPAIRs) in 6 photometric bands (70, 100, 160, 250, 350, and 500 μm). Among 132 spiral galaxies in the 44 spiral–spiral (S+S) pairs and 44 spiral–elliptical (S+E) pairs, 113 are detected in at least 1 Herschel band. The star formation rate (SFR) and dust mass (M dust ) are derived from the IR SED fitting. The mass of total gas (M gas ) is estimated by assuming a constant dust-to-gas mass ratio of 0.01. Star-forming spiral galaxies (SFGs) in S+S pairs show significant enhancements in both specific star formation rate (sSFR) and star formation efficiency (SFE), while having nearly the same gas mass compared to control galaxies. On the other hand, for SFGs in S+E pairs, there is no significant sSFR enhancement and the mean SFE enhancement is significantly lower than that of SFGs in S+S pairs. This suggests an important role for the disk–disk collision in the interaction-induced star formation. The M gas of SFGs in S+E pairs is marginally lower than that of their counterparts in both S+S pairs and the control sample. Paired galaxies with and without interaction signs do not differ significantly in their mean sSFR and SFE. As found in previous works, this much larger sample confirms that the primary and secondary spirals in S+S pairs follow a Holmberg effect correlation on sSFR

  18. Galaxy pairs in the SDSS - XIII. The connection between enhanced star formation and molecular gas properties in galaxy mergers

    Science.gov (United States)

    Violino, Giulio; Ellison, Sara L.; Sargent, Mark; Coppin, Kristen E. K.; Scudder, Jillian M.; Mendel, Trevor J.; Saintonge, Amelie

    2018-05-01

    We investigate the connection between star formation and molecular gas properties in galaxy mergers at low redshift (z ≤ 0.06). The study we present is based on IRAM 30-m CO(1-0) observations of 11 galaxies with a close companion selected from the Sloan Digital Sky Survey (SDSS). The pairs have mass ratios ≤4, projected separations rp ≤ 30 kpc and velocity separations ΔV ≤ 300 km s-1, and have been selected to exhibit enhanced specific star formation rates (sSFRs). We calculate molecular gas (H2) masses, assigning to each galaxy a physically motivated conversion factor αCO, and we derive molecular gas fractions and depletion times. We compare these quantities with those of isolated galaxies from the extended CO Legacy Data base for the GALEX Arecibo SDSS Survey sample (xCOLDGASS; Saintonge et al.) with gas quantities computed in an identical way. Ours is the first study which directly compares the gas properties of galaxy pairs and those of a control sample of normal galaxies with rigorous control procedures and for which SFR and H2 masses have been estimated using the same method. We find that the galaxy pairs have shorter depletion times and an average molecular gas fraction enhancement of 0.4 dex compared to the mass matched control sample drawn from xCOLDGASS. However, the gas masses (and fractions) in galaxy pairs and their depletion times are consistent with those of non-mergers whose SFRs are similarly elevated. We conclude that both external interactions and internal processes may lead to molecular gas enhancement and decreased depletion times.

  19. The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum

    Science.gov (United States)

    Margutti, R.; Alexander, K. D.; Xie, X.; Sironi, L.; Metzger, B. D.; Kathirgamaraju, A.; Fong, W.; Blanchard, P. K.; Berger, E.; MacFadyen, A.; Giannios, D.; Guidorzi, C.; Hajela, A.; Chornock, R.; Cowperthwaite, P. S.; Eftekhari, T.; Nicholl, M.; Villar, V. A.; Williams, P. K. G.; Zrake, J.

    2018-03-01

    We report deep Chandra X-ray Observatory (CXO), Hubble Space Telescope (HST), and Karl J. Jansky Very Large Array (VLA) observations of the binary neutron star event GW170817 at t spectrum extending for eight orders of magnitude in frequency enables the most precise measurement of the index p of the distribution of non-thermal relativistic electrons N(γ )\\propto {γ }-p accelerated by a shock launched by a neutron star (NS)–NS merger to date. We find p = 2.17 ± 0.01, which indicates that radiation from ejecta with Γ ∼ 3–10 dominates the observed emission. While constraining the nature of the emission process, these observations do not constrain the nature of the relativistic ejecta. We employ simulations of explosive outflows launched in NS ejecta clouds to show that the spectral and temporal evolution of the non-thermal emission from GW170817 is consistent with both emission from radially stratified quasi-spherical ejecta traveling at mildly relativistic speeds, and emission from off-axis collimated ejecta characterized by a narrow cone of ultra-relativistic material with slower wings extending to larger angles. In the latter scenario, GW170817 harbored a normal short gamma-ray burst (SGRB) directed away from our line of sight. Observations at t ≤ 200 days are unlikely to settle the debate, as in both scenarios the observed emission is effectively dominated by radiation from mildly relativistic material.

  20. COSMIC EVOLUTION OF STAR FORMATION ENHANCEMENT IN CLOSE MAJOR-MERGER GALAXY PAIRS SINCE z = 1

    International Nuclear Information System (INIS)

    Xu, C. K.; Shupe, D. L.; Bock, J.; Bridge, C.; Cooray, A.; Lu, N.; Schulz, B.; Béthermin, M.; Aussel, H.; Elbaz, D.; Le Floc'h, E.; Riguccini, L.; Berta, S.; Lutz, D.; Magnelli, B.; Conley, A.; Franceschini, A.; Marsden, G.; Oliver, S. J.; Pozzi, F.

    2012-01-01

    The infrared (IR) emission of 'M * galaxies' (10 10.4 ≤ M star ≤ 10 11.0 M ☉ ) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of ∼10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs.

  1. Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

    Science.gov (United States)

    Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

    2000-08-01

    We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (rstandard models of photoionization, shocks, and starbursts). We present four detailed emission

  2. THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS

    International Nuclear Information System (INIS)

    Eichler, M.; Panov, I.; Rauscher, T.; Thielemann, F.-K.; Arcones, A.; Langanke, K.; Martinez-Pinedo, G.; Kelic, A.; Korobkin, O.; Rosswog, S.; Marketin, T.; Winteler, C.; Zinner, N. T.

    2015-01-01

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree–Fock–Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)–(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well

  3. THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS

    Energy Technology Data Exchange (ETDEWEB)

    Eichler, M.; Panov, I.; Rauscher, T.; Thielemann, F.-K. [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland); Arcones, A.; Langanke, K.; Martinez-Pinedo, G. [Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstrasse 2, D-64289 Darmstadt (Germany); Kelic, A. [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany); Korobkin, O.; Rosswog, S. [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Marketin, T. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia); Winteler, C. [Institut Energie am Bau, Fachhochschule Nordwestschweiz, St. Jakobs-Strasse 84, 4132 Muttenz (Switzerland); Zinner, N. T., E-mail: marius.eichler@unibas.ch [Department of Physics and Astronomy, Aarhus University, Ny Munkegade, bygn. 1520, DK-8000 Aarhus C (Denmark)

    2015-07-20

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree–Fock–Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)–(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  4. Decoding Galactic Merger Histories

    Directory of Open Access Journals (Sweden)

    Eric F. Bell

    2017-12-01

    Full Text Available Galaxy mergers are expected to influence galaxy properties, yet measurements of individual merger histories are lacking. Models predict that merger histories can be measured using stellar halos and that these halos can be quantified using observations of resolved stars along their minor axis. Such observations reveal that Milky Way-mass galaxies have a wide range of stellar halo properties and show a correlation between their stellar halo masses and metallicities. This correlation agrees with merger-driven models where stellar halos are formed by satellite galaxy disruption. In these models, the largest accreted satellite dominates the stellar halo properties. Consequently, the observed diversity in the stellar halos of Milky Way-mass galaxies implies a large range in the masses of their largest merger partners. In particular, the Milky Way’s low mass halo implies an unusually quiet merger history. We used these measurements to seek predicted correlations between the bulge and central black hole (BH mass and the mass of the largest merger partner. We found no significant correlations: while some galaxies with large bulges and BHs have large stellar halos and thus experienced a major or minor merger, half have small stellar halos and never experienced a significant merger event. These results indicate that bulge and BH growth is not solely driven by merger-related processes.

  5. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta

    Energy Technology Data Exchange (ETDEWEB)

    Nicholl, M.; Berger, E.; Kasen, D.; Metzger, B. D.; Elias, J.; Briceño, C.; Alexander, K. D.; Blanchard, P. K.; Chornock, R.; Cowperthwaite, P. S.; Eftekhari, T.; Fong, W.; Margutti, R.; Villar, V. A.; Williams, P. K. G.; Brown, W.; Annis, J.; Bahramian, A.; Brout, D.; Brown, D. A.; Chen, H. -Y.; Clemens, J. C.; Dennihy, E.; Dunlap, B.; Holz, D. E.; Marchesini, E.; Massaro, F.; Moskowitz, N.; Pelisoli, I.; Rest, A.; Ricci, F.; Sako, M.; Soares-Santos, M.; Strader, J.

    2017-10-16

    We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the SOAR and Magellan telescopes; the UV spectrum was obtained with the \\textit{Hubble Space Telescope} at 5.5 days. Our data reveal a rapidly-fading blue component ($T\\approx5500$ K at 1.5 days) that quickly reddens; spectra later than $\\gtrsim 4.5$ days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at $\\sim 7900$ \\AA\\ at $t\\lesssim 4.5$ days. The colours, rapid evolution and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light $r$-process nuclei with atomic mass number $A\\lesssim 140$. This indicates a sight-line within $\\theta_{\\rm obs}\\lesssim 45^{\\circ}$ of the orbital axis. Comparison to models suggests $\\sim0.03$ M$_\\odot$ of blue ejecta, with a velocity of $\\sim 0.3c$. The required lanthanide fraction is $\\sim 10^{-4}$, but this drops to $<10^{-5}$ in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of $\\lesssim 12$ km. This mass also supports the idea that neutron star mergers are a major contributor to $r$-process nucleosynthesis.

  6. Concluding Remarks: Connecting Relativistic Heavy Ion Collisions and Neutron Star Mergers by the Equation of State of Dense Hadron- and Quark Matter as signalled by Gravitational Waves

    Science.gov (United States)

    Hanauske, Matthias; Steinheimer, Jan; Bovard, Luke; Mukherjee, Ayon; Schramm, Stefan; Takami, Kentaro; Papenfort, Jens; Wechselberger, Natascha; Rezzolla, Luciano; Stöcker, Horst

    2017-07-01

    The underlying open questions in the fields of general relativistic astrophysics and elementary particle and nuclear physics are strongly connected and their results are interdependent. Although the physical systems are quite different, the 4D-simulation of a merger of a binary system of two neutron stars and the properties of the hot and dense matter created in high energy heavy ion collisions, strongly depend on the equation of state of fundamental elementary matter. Neutron star mergers represent optimal astrophysical laboratories to investigate the QCD phase structure using a spectrogram of the post-merger phase of the emitted gravitational waves. These studies can be supplemented by observations from heavy ion collisions to possibly reach a conclusive picture on the QCD phase structure at high density and temperature. As gravitational waves (GWs) emitted from merging neutron star binaries are on the verge of their first detection, it is important to understand the main characteristics of the underlying merging system in order to predict the expected GW signal. Based on numerical-relativity simulations of merging neutron star binaries, the emitted GW and the interior structure of the generated hypermassive neutron stars (HMNS) have been analyzed in detail. This article will focus on the internal and rotational HMNS properties and their connection with the emitted GW signal. Especially, the appearance of the hadon-quark phase transition in the interior region of the HMNS and its conjunction with the spectral properties of the emitted GW will be addressed and confronted with the simulation results of high energy heavy ion collisions.

  7. Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers

    Science.gov (United States)

    Wollaeger, Ryan T.; Korobkin, Oleg; Fontes, Christopher J.; Rosswog, Stephan K.; Even, Wesley P.; Fryer, Christopher L.; Sollerman, Jesper; Hungerford, Aimee L.; van Rossum, Daniel R.; Wollaber, Allan B.

    2018-04-01

    The electromagnetic transients accompanying compact binary mergers (γ-ray bursts, afterglows and 'macronovae') are crucial to pinpoint the sky location of gravitational wave sources. Macronovae are caused by the radioactivity from freshly synthesised heavy elements, e.g. from dynamic ejecta and various types of winds. We study macronova signatures by using multi-dimensional radiative transfer calculations. We employ the radiative transfer code SuperNu and state-of-the art LTE opacities for a few representative elements from the wind and dynamical ejecta (Cr, Pd, Se, Te, Br, Zr, Sm, Ce, Nd, U) to calculate synthetic light curves and spectra for a range of ejecta morphologies. The radioactive power of the resulting macronova is calculated with the detailed input of decay products. We assess the detection prospects for our most complex models, based on the portion of viewing angles that are sufficiently bright, at different cosmological redshifts (z). The brighter emission from the wind is unobscured by the lanthanides (or actinides) in some of the models, permitting non-zero detection probabilities for redshifts up to z = 0.07. We also find the nuclear mass model and the resulting radioactive heating rate are crucial for the detectability. While for the most pessimistic heating rate (from the FRDM model) no reasonable increase in the ejecta mass or velocity, or wind mass or velocity, can possibly make the light curves agree with the observed nIR excess after GRB130603B, a more optimistic heating rate (from the Duflo-Zuker model) leads to good agreement. We conclude that future reliable macronova observations would constrain nuclear heating rates, and consequently help constrain nuclear mass models.

  8. Early Soft X-Ray to UV Emission from Double Neutron Star Mergers: Implications from the Long-term Observations of GW170817

    Science.gov (United States)

    Wang, Xiang-Yu; Huang, Zhi-Qiu

    2018-01-01

    Recent long-term radio follow-up observations of GW170817 reveal a simple power-law rising light curve, with a slope of {t}0.78, up to 93 days after the merger. The latest X-ray detection at 109 days is also consistent with such a temporal slope. Such a shallow rise behavior requires a mildly relativistic outflow with a steep velocity gradient profile, so that slower material with larger energy catches up with the decelerating ejecta and re-energizes it. It has been suggested that this mildly relativistic outflow may represent a cocoon of material. We suggest that the velocity gradient profile may form during the stage that the cocoon is breaking out of the merger ejecta, resulting from shock propagation down a density gradient. The cooling of the hot relativistic cocoon material immediately after it breaks out should have produced soft X-ray to UV radiation at tens of seconds to hours after the merger. The soft X-ray emission has a luminosity of {L}{{X}}∼ {10}45 {erg} {{{s}}}-1 over a period of tens of seconds for a merger event like GW170817. The UV emission shows a rise initially and peaks at about a few hours with a luminosity of {L}{UV}∼ {10}42 {erg} {{{s}}}-1. The soft X-ray transients could be detected by future wide-angle X-ray detectors, such as the Chinese mission Einstein Probe. This soft X-ray/UV emission would serve as one of the earliest electromagnetic counterparts of gravitation waves from double neutron star mergers and could provide the earliest localization of the sources.

  9. Bimodal Long-lasting Components in Short Gamma-Ray Bursts: Promising Electromagnetic Counterparts to Neutron Star Binary Mergers

    Energy Technology Data Exchange (ETDEWEB)

    Kisaka, Shota; Sakamoto, Takanori [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa, 252-5258 (Japan); Ioka, Kunihito, E-mail: kisaka@phys.aoyama.ac.jp, E-mail: tsakamoto@phys.aoyama.ac.jp, E-mail: kunihito.ioka@yukawa.kyoto-u.ac.jp [Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2017-09-10

    Long-lasting emission of short gamma-ray bursts (GRBs) is crucial to reveal the physical origin of the central engine as well as to detect electromagnetic (EM) counterparts to gravitational waves (GWs) from neutron star binary mergers. We investigate 65 X-ray light curves of short GRBs, which is six times more than previous studies, by combining both Swift /BAT and XRT data. The light curves are found to consist of two distinct components at >5 σ with bimodal distributions of luminosity and duration, i.e., extended (with a timescale of ≲10{sup 3} s) and plateau emission (with a timescale of ≳10{sup 3} s), which are likely the central engine activities, but not afterglows. The extended emission has an isotropic energy comparable to the prompt emission, while the plateau emission has ∼0.01–1 times this energy. Half (50%) of our sample has both components, while the other half is consistent with having both components. This leads us to conjecture that almost all short GRBs have both the extended and plateau emission. The long-lasting emission can be explained by the jets from black holes with fallback ejecta, and could power macronovae (or kilonovae) like GRB 130603B and GRB 160821B. Based on the observed properties, we quantify the detectability of EM counterparts to GWs, including the plateau emission scattered to the off-axis angle, with CALET /HXM, INTEGRAL /SPI-ACS, Fermi /GBM, MAXI /GSC, Swift /BAT, XRT, the future ISS-Lobster /WFI, Einstein Probe /WXT, and eROSITA .

  10. Merger driven star-formation activity in Cl J1449+0856 at z=1.99 as seen by ALMA and JVLA

    Science.gov (United States)

    Coogan, R. T.; Daddi, E.; Sargent, M. T.; Strazzullo, V.; Valentino, F.; Gobat, R.; Magdis, G.; Bethermin, M.; Pannella, M.; Onodera, M.; Liu, D.; Cimatti, A.; Dannerbauer, H.; Carollo, M.; Renzini, A.; Tremou, E.

    2018-06-01

    We use ALMA and JVLA observations of the galaxy cluster Cl J1449+0856 at z=1.99, in order to study how dust-obscured star-formation, ISM content and AGN activity are linked to environment and galaxy interactions during the crucial phase of high-z cluster assembly. We present detections of multiple transitions of 12CO, as well as dust continuum emission detections from 11 galaxies in the core of Cl J1449+0856. We measure the gas excitation properties, star-formation rates, gas consumption timescales and gas-to-stellar mass ratios for the galaxies. We find evidence for a large fraction of galaxies with highly-excited molecular gas, contributing >50% to the total SFR in the cluster core. We compare these results with expectations for field galaxies, and conclude that environmental influences have strongly enhanced the fraction of excited galaxies in this cluster. We find a dearth of molecular gas in the galaxies' gas reservoirs, implying a high star-formation efficiency (SFE) in the cluster core, and find short gas depletion timescales τdepstar-formation rates (sSFRs) in the cluster galaxies, despite their high SFEs and gas excitations. We find evidence for a large number of mergers in the cluster core, contributing a large fraction of the core's total star-formation compared with expectations in the field. We conclude that the environmental impact on the galaxy excitations is linked to the high rate of galaxy mergers, interactions and active galactic nuclei in the cluster core.

  11. Starburst to Quiescent from HST/ALMA: Stars and Dust Unveil Minor Mergers in Submillimeter Galaxies at z ∼ 4.5

    Science.gov (United States)

    Gómez-Guijarro, C.; Toft, S.; Karim, A.; Magnelli, B.; Magdis, G. E.; Jiménez-Andrade, E. F.; Capak, P. L.; Fraternali, F.; Fujimoto, S.; Riechers, D. A.; Schinnerer, E.; Smolčić, V.; Aravena, M.; Bertoldi, F.; Cortzen, I.; Hasinger, G.; Hu, E. M.; Jones, G. C.; Koekemoer, A. M.; Lee, N.; McCracken, H. J.; Michałowski, M. J.; Navarrete, F.; Pović, M.; Puglisi, A.; Romano-Díaz, E.; Sheth, K.; Silverman, J. D.; Staguhn, J.; Steinhardt, C. L.; Stockmann, M.; Tanaka, M.; Valentino, F.; van Kampen, E.; Zirm, A.

    2018-04-01

    Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z ≥ 3 have been proposed as progenitors of z ≥ 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust, and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ∼ 4.5. The stellar UV emission probed by HST is extended and irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical, finding that the systems are undergoing minor mergers with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median r e = 0.70 ± 0.29 kpc), and it is in all cases associated with the most massive component of the mergers (median {log}({M}* /{M}ȯ )=10.49+/- 0.32). We compare spatially resolved UV slope (β) maps with the FIR dust continuum to study the infrared excess (IRX = L IR/L UV)–β relation. The SMGs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass–size plane at smaller stellar masses and sizes than the cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations.

  12. BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

    International Nuclear Information System (INIS)

    Deaton, M. Brett; Duez, Matthew D.; Foucart, Francois; O'Connor, Evan; Ott, Christian D.; Scheel, Mark A.; Szilagyi, Bela; Kidder, Lawrence E.; Muhlberger, Curran D.

    2013-01-01

    Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron star mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state (EOS) and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 M ☉ neutron star, 5.6 M ☉ black hole), high-spin (black hole J/M 2 = 0.9) system with the K 0 = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M ☉ of nuclear matter is ejected from the system, while another 0.3 M ☉ forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Y e of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ∼ 6 MeV) and luminous in neutrinos (L ν ∼ 10 54 erg s –1 ), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution

  13. Three-Dimensional General-Relativistic Magnetohydrodynamic Simulations of Remnant Accretion Disks from Neutron Star Mergers: Outflows and r-Process Nucleosynthesis.

    Science.gov (United States)

    Siegel, Daniel M; Metzger, Brian D

    2017-12-08

    The merger of binary neutron stars, or of a neutron star and a stellar-mass black hole, can result in the formation of a massive rotating torus around a spinning black hole. In addition to providing collimating media for γ-ray burst jets, unbound outflows from these disks are an important source of mass ejection and rapid neutron capture (r-process) nucleosynthesis. We present the first three-dimensional general-relativistic magnetohydrodynamic (GRMHD) simulations of neutrino-cooled accretion disks in neutron star mergers, including a realistic equation of state valid at low densities and temperatures, self-consistent evolution of the electron fraction, and neutrino cooling through an approximate leakage scheme. After initial magnetic field amplification by magnetic winding, we witness the vigorous onset of turbulence driven by the magnetorotational instability (MRI). The disk quickly reaches a balance between heating from MRI-driven turbulence and neutrino cooling, which regulates the midplane electron fraction to a low equilibrium value Y_{e}≈0.1. Over the 380-ms duration of the simulation, we find that a fraction ≈20% of the initial torus mass is unbound in powerful outflows with asymptotic velocities v≈0.1c and electron fractions Y_{e}≈0.1-0.25. Postprocessing the outflows through a nuclear reaction network shows the production of a robust second- and third-peak r process. Though broadly consistent with the results of previous axisymmetric hydrodynamical simulations, extrapolation of our results to late times suggests that the total ejecta mass from GRMHD disks is significantly higher. Our results provide strong evidence that postmerger disk outflows are an important site for the r process.

  14. BLACK HOLE-NEUTRON STAR MERGERS AND SHORT GAMMA-RAY BURSTS: A RELATIVISTIC TOY MODEL TO ESTIMATE THE MASS OF THE TORUS

    International Nuclear Information System (INIS)

    Pannarale, Francesco; Tonita, Aaryn; Rezzolla, Luciano

    2011-01-01

    The merger of a binary system composed of a black hole (BH) and a neutron star (NS) may leave behind a torus of hot, dense matter orbiting around the BH. While numerical-relativity simulations are necessary to simulate this process accurately, they are also computationally expensive and unable at present to cover the large space of possible parameters, which include the relative mass ratio, the stellar compactness, and the BH spin. To mitigate this and provide a first reasonable coverage of the space of parameters, we have developed a method for estimating the mass of the remnant torus from BH-NS mergers. The toy model makes use of an improved relativistic affine model to describe the tidal deformations of an extended tri-axial ellipsoid orbiting around a Kerr BH and measures the mass of the remnant torus by considering which of the fluid particles composing the star are on bound orbits at the time of the tidal disruption. We tune the toy model by using the results of fully general-relativistic simulations obtaining relative precisions of a few percent and use it to investigate the space of parameters extensively. In this way, we find that the torus mass is largest for systems with highly spinning BHs, small stellar compactnesses, and large mass ratios. As an example, tori as massive as M b,tor ≅ 1.33 M sun can be produced for a very extended star with compactness C ≅ 0.1 inspiralling around a BH with dimensionless spin parameter a = 0.85 and mass ratio q ≅ 0.3. However, for a more astrophysically reasonable mass ratio q ≅ 0.14 and a canonical value of the stellar compactness C ≅ 0.145, the toy model sets a considerably smaller upper limit of M b,tor ∼ sun .

  15. Mixing processes in galaxy mergers

    International Nuclear Information System (INIS)

    White, S.D.M.

    1980-01-01

    Previously published simulations of mergers between galaxies are used to examine the degree to which population gradients are weakened during the coalescence of two or more stellar systems. Although substantial mixing occurs during a merger, its effect on such gradients is quite moderate and can be overwhelmed by the effect of changes in structure. Experiment suggests that the centre-to-edge population difference in a merger remnant will be 20 per cent smaller than that in its progenitor galaxies if these are identical centrally concentrated systems. A sequence of three binary mergers is thus required to reduce such differences by a factor of 2. Because of changes in radial structure, population gradients are, in general, reduced more rapidly than is suggested by these numbers. Mixing is more efficient in mergers between less concentrated systems. In real merger remnants any weakening of gradients may often be masked by star-formation in residual interstellar gas. (author)

  16. ALMA and GMRT Constraints on the Off-axis Gamma-Ray Burst 170817A from the Binary Neutron Star Merger GW170817

    Science.gov (United States)

    Kim, S.; Schulze, S.; Resmi, L.; González-López, J.; Higgins, A. B.; Ishwara-Chandra, C. H.; Bauer, F. E.; de Gregorio-Monsalvo, I.; De Pasquale, M.; de Ugarte Postigo, A.; Kann, D. A.; Martín, S.; Oates, S. R.; Starling, R. L. C.; Tanvir, N. R.; Buchner, J.; Campana, S.; Cano, Z.; Covino, S.; Fruchter, A. S.; Fynbo, J. P. U.; Hartmann, D. H.; Hjorth, J.; Jakobsson, P.; Levan, A. J.; Malesani, D.; Michałowski, M. J.; Milvang-Jensen, B.; Misra, K.; O’Brien, P. T.; Sánchez-Ramírez, R.; Thöne, C. C.; Watson, D. J.; Wiersema, K.

    2017-12-01

    Binary neutron-star mergers (BNSMs) are among the most readily detectable gravitational-wave (GW) sources with the Laser Interferometer Gravitational-wave Observatory (LIGO). They are also thought to produce short γ-ray bursts (SGRBs) and kilonovae that are powered by r-process nuclei. Detecting these phenomena simultaneously would provide an unprecedented view of the physics during and after the merger of two compact objects. Such a Rosetta Stone event was detected by LIGO/Virgo on 2017 August 17 at a distance of ∼44 Mpc. We monitored the position of the BNSM with Atacama Large Millimeter/submillimeter Array (ALMA) at 338.5 GHz and the Giant Metrewave Radio Telescope (GMRT) at 1.4 GHz, from 1.4 to 44 days after the merger. Our observations rule out any afterglow more luminous than 3× {10}26 {erg} {{{s}}}-1 {{Hz}}-1 in these bands, probing >2–4 dex fainter than previous SGRB limits. We match these limits, in conjunction with public data announcing the appearance of X-ray and radio emission in the weeks after the GW event, to templates of off-axis afterglows. Our broadband modeling suggests that GW170817 was accompanied by an SGRB and that the γ-ray burst (GRB) jet, powered by {E}{AG,{iso}}∼ {10}50 erg, had a half-opening angle of ∼ 20^\\circ , and was misaligned by ∼ 41^\\circ from our line of sight. The data are also consistent with a more collimated jet: {E}{AG,{iso}}∼ {10}51 erg, {θ }1/2,{jet}∼ 5^\\circ ,{θ }{obs}∼ 17^\\circ . This is the most conclusive detection of an off-axis GRB afterglow and the first associated with a BNSM-GW event to date. We use the viewing angle estimates to infer the initial bulk Lorentz factor and true energy release of the burst.

  17. BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

    Energy Technology Data Exchange (ETDEWEB)

    Deaton, M. Brett; Duez, Matthew D. [Department of Physics and Astronomy, Washington State University, Pullman, WA 99164 (United States); Foucart, Francois; O' Connor, Evan [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario M5S 3H8 (Canada); Ott, Christian D.; Scheel, Mark A.; Szilagyi, Bela [TAPIR, MC 350-17, California Institute of Technology, Pasadena, CA 91125 (United States); Kidder, Lawrence E.; Muhlberger, Curran D., E-mail: mbdeaton@wsu.edu, E-mail: m.duez@wsu.edu [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)

    2013-10-10

    Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron star mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state (EOS) and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 M{sub ☉} neutron star, 5.6 M{sub ☉} black hole), high-spin (black hole J/M {sup 2} = 0.9) system with the K{sub 0} = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M{sub ☉} of nuclear matter is ejected from the system, while another 0.3 M{sub ☉} forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Y{sub e} of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ∼ 6 MeV) and luminous in neutrinos (L{sub ν} ∼ 10{sup 54} erg s{sup –1}), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution.

  18. Neutron star/red giant encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1988-01-01

    The author presents a simple expression for the amount by which xsub(crit) is diminished as a star evolves xsub(crit) Rsub(crit)/R*, where Rsub(crit) is the maximum distance of closest approach between two stars for which the tidal energy is sufficient to bind the system, and R* is the radius of the star on which tides are being raised. Also it is concluded that tidal capture of giants by neutron stars resulting in binary systems is unlikely in globular clusters. However, collisions between neutron stars and red giants, or an alternative process involving tidal capture of a main-sequence star into an initially detached binary system, may result either in rapidly rotating neutron stars or in white dwarf/neutron star binaries. (author)

  19. Origin of the early-type R stars: a binary-merger solution to a century-old problem?

    NARCIS (Netherlands)

    Izzard, R.G.; Jeffery, C.S.; Lattanzio, J.C.

    2007-01-01

    The early-R stars are carbon-rich K-type giants. They are enhanced in C12, C13 and N14, have approximately solar oxygen, magnesium isotopes, s-process and iron abundances, have the luminosity of core-helium burning stars, are not rapid rotators, are members of the Galactic thick disk and, most

  20. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r -process Nucleosynthesis with Gemini-South

    Energy Technology Data Exchange (ETDEWEB)

    Chornock, R. [Astrophysical Institute, Department of Physics and Astronomy, 251B Clippinger Lab, Ohio University, Athens, OH 45701 (United States); Berger, E.; Cowperthwaite, P. S.; Nicholl, M.; Villar, V. A.; Alexander, K. D.; Blanchard, P. K.; Eftekhari, T.; Williams, P. K. G. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kasen, D. [Departments of Physics and Astronomy, and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720-7300 (United States); Fong, W.; Margutti, R. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States); Annis, J.; Frieman, J. A. [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Brout, D. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Brown, D. A. [Department of Physics, Syracuse University, Syracuse NY 13224 (United States); Chen, H.-Y. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Drout, M. R. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Farr, B. [Department of Physics, University of Oregon, Eugene, OR 97403 (United States); Foley, R. J., E-mail: chornock@ohio.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); and others

    2017-10-20

    We present a near-infrared spectral sequence of the electromagnetic counterpart to the binary neutron star merger GW170817 detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo. Our data set comprises seven epochs of J + H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after the merger. In the initial epoch, the spectrum is dominated by a smooth blue continuum due to a high-velocity, lanthanide-poor blue kilonova component. Starting the following night, all of the subsequent spectra instead show features that are similar to those predicted in model spectra of material with a high concentration of lanthanides, including spectral peaks near 1.07 and 1.55 μ m. Our fiducial model with 0.04 M {sub ⊙} of ejecta, an ejection velocity of v = 0.1 c , and a lanthanide concentration of X {sub lan} = 10{sup −2} provides a good match to the spectra taken in the first five days, although it over-predicts the late-time fluxes. We also explore models with multiple fitting components, in each case finding that a significant abundance of lanthanide elements is necessary to match the broad spectral peaks that we observe starting at 2.5 days after the merger. These data provide direct evidence that binary neutron star mergers are significant production sites of even the heaviest r -process elements.

  1. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models

    Energy Technology Data Exchange (ETDEWEB)

    Cowperthwaite, P. S.; Berger, E.; Villar, V. A.; Metzger, B. D.; Nicholl, M.; Chornock, R.; Blanchard, P. K.; Fong, W.; Margutti, R.; Soares-Santos, M.; Alexander, K. D.; Allam, S.; Annis, J.; Brout, D.; Brown, D. A.; Butler, R. E.; Chen, H. -Y.; Diehl, H. T.; Doctor, Z.; Drout, M. R.; Eftekhari, T.; Farr, B.; Finley, D. A.; Foley, R. J.; Frieman, J. A.; Fryer, C. L.; García-Bellido, J.; Gill, M. S. S.; Guillochon, J.; Herner, K.; Holz, D. E.; Kasen, D.; Kessler, R.; Marriner, J.; Matheson, T.; Neilsen, E. H.; Quataert, E.; Palmese, A.; Rest, A.; Sako, M.; Scolnic, D. M.; Smith, N.; Tucker, D. L.; Williams, P. K. G.; Balbinot, E.; Carlin, J. L.; Cook, E. R.; Durret, F.; Li, T. S.; Lopes, P. A. A.; Lourenço, A. C. C.; Marshall, J. L.; Medina, G. E.; Muir, J.; Muñoz, R. R.; Sauseda, M.; Schlegel, D. J.; Secco, L. F.; Vivas, A. K.; Wester, W.; Zenteno, A.; Zhang, Y.; Abbott, T. M. C.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bertin, E.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Castander, F. J.; Crocce, M.; Cunha, C. E.; D’Andrea, C. B.; Costa, L. N. da; Davis, C.; DePoy, D. L.; Desai, S.; Dietrich, J. P.; Drlica-Wagner, A.; Eifler, T. F.; Evrard, A. E.; Fernandez, E.; Flaugher, B.; Fosalba, P.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Johnson, M. W. G.; Johnson, M. D.; Kent, S.; Krause, E.; Kron, R.; Kuehn, K.; Nuropatkin, N.; Lahav, O.; Lima, M.; Lin, H.; Maia, M. A. G.; March, M.; Martini, P.; McMahon, R. G.; Menanteau, F.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Neilsen, E.; Nichol, R. C.; Ogando, R. L. C.; Plazas, A. A.; Roe, N.; Romer, A. K.; Roodman, A.; Rykoff, E. S.; Sanchez, E.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, M.; Smith, R. C.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Thomas, R. C.; Troxel, M. A.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Yanny, B.; Zuntz, J.

    2017-10-16

    We present UV, optical, and NIR photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced LIGO/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at $0.47$ days to $18.5$ days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-South/FLAMINGOS-2 (GS/F2), and the {\\it Hubble Space Telescope} ({\\it HST}). The spectral energy distribution (SED) inferred from this photometry at $0.6$ days is well described by a blackbody model with $T\\approx 8300$ K, a radius of $R\\approx 4.5\\times 10^{14}$ cm (corresponding to an expansion velocity of $v\\approx 0.3c$), and a bolometric luminosity of $L_{\\rm bol}\\approx 5\\times10^{41}$ erg s$^{-1}$. At $1.5$ days we find a multi-component SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands and significant reddening of the optical/NIR colors. Modeling the entire data set we find that models with heating from radioactive decay of $^{56}$Ni, or those with only a single component of opacity from $r$-process elements, fail to capture the rapid optical decline and red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data, the resulting "blue" component has $M_\\mathrm{ej}^\\mathrm{blue}\\approx 0.01$ M$_\\odot$ and $v_\\mathrm{ej}^\\mathrm{blue}\\approx 0.3$c, and the "red" component has $M_\\mathrm{ej}^\\mathrm{red}\\approx 0.04$ M$_\\odot$ and $v_\\mathrm{ej}^\\mathrm{red}\\approx 0.1$c. These ejecta masses are broadly consistent with the estimated $r$-process production rate required to explain the Milky Way $r$-process abundances, providing the first evidence that BNS mergers can be a dominant site of $r$-process enrichment.

  2. THE DIRT ON DRY MERGERS

    International Nuclear Information System (INIS)

    Desai, Vandana; Soifer, B. T.; Dey, Arjun; Cohen, Emma; Le Floc'h, Emeric

    2011-01-01

    Using data from the Spitzer Space Telescope, we analyze the mid-infrared (3-70 μm) spectral energy distributions of dry merger candidates in the Booetes field of the NOAO Deep Wide-Field Survey. These candidates were selected by previous authors to be luminous, red, early-type galaxies with morphological evidence of recent tidal interactions. We find that a significant fraction of these candidates exhibit 8 and 24 μm excesses compared to expectations for old stellar populations. We estimate that a quarter of dry merger candidates have mid-infrared-derived star formation rates greater than ∼1 M sun yr -1 . This represents a 'frosting' on top of a large old stellar population, and has been seen in previous studies of elliptical galaxies. Further, the dry merger candidates include a higher fraction of star-forming galaxies relative to a control sample without tidal features. We therefore conclude that the star formation in these massive ellipticals is likely triggered by merger activity. Our data suggest that the mergers responsible for the observed tidal features were not completely dry, and may be minor mergers involving a gas-rich dwarf galaxy.

  3. The role of fission on neutron star mergers and its impact on the r-process peaks

    International Nuclear Information System (INIS)

    Eichler, M.; Thielemann, F.-K.; Arcones, A.; Langanke, K.; Martinez-Pinedo, G.; Kelic, A.; Korobkin, O.; Rosswog, S.; Marketin, T.; Panov, I.; Rauscher, T.; Winteler, C.; Zinner, N. T.

    2016-01-01

    The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations using four different fission fragment distribution models. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which has been noticed in a number of merger nucleosynthesis predictions. We show that this shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  4. The role of fission on neutron star mergers and its impact on the r-process peaks

    Energy Technology Data Exchange (ETDEWEB)

    Eichler, M., E-mail: marius.eichler@unibas.ch; Thielemann, F.-K. [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel (Switzerland); Arcones, A.; Langanke, K.; Martinez-Pinedo, G. [Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstrasse 2, D-64289 Darmstadt (Germany); GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany); Kelic, A. [GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany); Korobkin, O.; Rosswog, S. [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-10691 Stockholm (Sweden); Marketin, T. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia); Panov, I. [SSC RF ITEP of NRC “Kurchatov Institute”, Bolshaya Cheremushkinskaya 25, 117218 Moscow (Russian Federation); Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel (Switzerland); Rauscher, T. [Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel (Switzerland); Winteler, C. [Institut Energie am Bau, Fachhochschule Nordwestschweiz, St. Jakobs-Strasse 84, 4132 Muttenz (Switzerland); Zinner, N. T. [Department of Physics and Astronomy, Aarhus University, Ny Munkegade, bygn. 1520, DK-8000 Aarhus C (Denmark)

    2016-06-21

    The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations using four different fission fragment distribution models. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which has been noticed in a number of merger nucleosynthesis predictions. We show that this shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  5. Binary neutron star mergers and short gamma-ray bursts: Effects of magnetic field orientation, equation of state, and mass ratio

    Science.gov (United States)

    Kawamura, Takumu; Giacomazzo, Bruno; Kastaun, Wolfgang; Ciolfi, Riccardo; Endrizzi, Andrea; Baiotti, Luca; Perna, Rosalba

    2016-09-01

    We present fully general-relativistic magnetohydrodynamic simulations of the merger of binary neutron star (BNS) systems. We consider BNSs producing a hypermassive neutron star (HMNS) that collapses to a spinning black hole (BH) surrounded by a magnetized accretion disk in a few tens of ms. We investigate whether such systems may launch relativistic jets and hence power short gamma-ray bursts. We study the effects of different equations of state (EOSs), different mass ratios, and different magnetic field orientations. For all cases, we present a detailed investigation of the matter dynamics and of the magnetic field evolution, with particular attention to its global structure and possible emission of relativistic jets. The main result of this work is that we observe the formation of an organized magnetic field structure. This happens independently of EOS, mass ratio, and initial magnetic field orientation. We also show that those models that produce a longer-lived HMNS lead to a stronger magnetic field before collapse to a BH. Such larger fields make it possible, for at least one of our models, to resolve the magnetorotational instability and hence further amplify the magnetic field in the disk. However, by the end of our simulations, we do not (yet) observe a magnetically dominated funnel nor a relativistic outflow. With respect to the recent simulations of Ruiz et al. [Astrophys. J. 824, L6 (2016)], we evolve models with lower and more plausible initial magnetic field strengths and (for computational reasons) we do not evolve the accretion disk for the long time scales that seem to be required in order to see a relativistic outflow. Since all our models produce a similar ordered magnetic field structure aligned with the BH spin axis, we expect that the results found by Ruiz et al. (who only considered an equal-mass system with an ideal fluid EOS) should be general and—at least from a qualitative point of view—independent of the mass ratio, magnetic field

  6. Evolution of the magnetized, neutrino-cooled accretion disk in the aftermath of a black hole-neutron star binary merger

    Science.gov (United States)

    Hossein Nouri, Fatemeh; Duez, Matthew D.; Foucart, Francois; Deaton, M. Brett; Haas, Roland; Haddadi, Milad; Kidder, Lawrence E.; Ott, Christian D.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela

    2018-04-01

    Black hole-torus systems from compact binary mergers are possible engines for gamma-ray bursts (GRBs). During the early evolution of the postmerger remnant, the state of the torus is determined by a combination of neutrino cooling and magnetically driven heating processes, so realistic models must include both effects. In this paper, we study the postmerger evolution of a magnetized black hole-neutron star binary system using the Spectral Einstein Code (SpEC) from an initial postmerger state provided by previous numerical relativity simulations. We use a finite-temperature nuclear equation of state and incorporate neutrino effects in a leakage approximation. To achieve the needed accuracy, we introduce improvements to SpEC's implementation of general-relativistic magnetohydrodynamics (MHD), including the use of cubed-sphere multipatch grids and an improved method for dealing with supersonic accretion flows where primitive variable recovery is difficult. We find that a seed magnetic field triggers a sustained source of heating, but its thermal effects are largely cancelled by the accretion and spreading of the torus from MHD-related angular momentum transport. The neutrino luminosity peaks at the start of the simulation, and then drops significantly over the first 20 ms but in roughly the same way for magnetized and nonmagnetized disks. The heating rate and disk's luminosity decrease much more slowly thereafter. These features of the evolution are insensitive to grid structure and resolution, formulation of the MHD equations, and seed field strength, although turbulent effects are not fully converged.

  7. NuSTAR View of the Black Hole Wind in the Galaxy Merger IRAS F11119+3257

    Science.gov (United States)

    Tombesi, F.; Veilleux, S.; Meléndez, M.; Lohfink, A.; Reeves, J. N.; Piconcelli, E.; Fiore, F.; Feruglio, C.

    2017-12-01

    Galactic winds driven by active galactic nuclei (AGNs) have been invoked to play a fundamental role in the co-evolution between supermassive black holes and their host galaxies. Finding observational evidence of such feedback mechanisms is of crucial importance and it requires a multi-wavelength approach in order to compare winds at different scales and phases. In Tombesi et al., we reported the detection of a powerful ultra-fast outflow (UFO) in the Suzaku X-ray spectrum of the ultra-luminous infrared galaxy IRAS F11119+3257. The comparison with a galaxy-scale OH molecular outflow observed with Herschel in the same source supported the energy-conserving scenario for AGN feedback. The main objective of this work is to perform an independent check of the Suzaku results using the higher sensitivity and wider X-ray continuum coverage of NuSTAR. We clearly detect a highly ionized Fe K UFO in the 100 ks NuSTAR spectrum with parameters N H = (3.2 ± 1.5) × 1024 cm-2, log ξ = {4.0}-0.3+1.2 erg s-1 cm, and {v}{out}={0.253}-0.118+0.061c. The launching radius is likely at a distance of r ≥ 16r s from the black hole. The mass outflow rate is in the range of {\\dot{M}}{out} ≃ 0.5-2 M ⊙ yr-1. The UFO momentum rate and power are {\\dot{P}}{out} ≃ 0.5-2 L AGN/c and {\\dot{E}}{out} ≃ 7%-27% L AGN, respectively. The UFO parameters are consistent between the 2013 Suzaku and the 2015 NuSTAR observations. Only the column density is found to be variable, possibly suggesting a clumpy wind. The comparison with the energetics of molecular outflows estimated in infrared and millimeter wavelengths support a connection between the nuclear and galaxy-scale winds in luminous AGNs.

  8. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-time Emission from the Kilonova Ejecta

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, K. D.; Berger, E.; Fong, W.; Williams, P. K. G.; Guidorzi, C.; Margutti, R.; Metzger, B. D.; Annis, J.; Blanchard, P. K.; Brout, D.; Brown, D. A.; Chen, H. -Y.; Chornock, R.; Cowperthwaite, P. S.; Drout, M.; Eftekhari, T.; Frieman, J.; Holz, D. E.; Nicholl, M.; Rest, A.; Sako, M.; Soares-Santos, M.; Villar, V. A.

    2017-10-16

    We present Very Large Array (VLA) and Atacama Large Millimeter/sub-millimeter Array ALMA radio observations of GW\\,170817, the first Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from a binary neutron star merger and the first GW event with an electromagnetic (EM) counterpart. Our data include the first observations following the discovery of the optical transient at both the centimeter ($13.7$ hours post merger) and millimeter ($2.41$ days post merger) bands. We detect faint emission at 6 GHz at 19.47 and 39.23 days after the merger, but not in an earlier observation at 2.46 d. We do not detect cm/mm emission at the position of the optical counterpart at frequencies of 10-97.5 GHz at times ranging from 0.6 to 30 days post merger, ruling out an on-axis short gamma-ray burst (SGRB) for energies $\\gtrsim 10^{48}$ erg. For fiducial SGRB parameters, our limits require an observer viewer angle of $\\gtrsim 20^{\\circ}$. The radio and X-ray data can be jointly explained as the afterglow emission from an SGRB with a jet energy of $\\sim 10^{49}-10^{50}$ erg that exploded in a uniform density environment with $n\\sim 10^{-4}-10^{-2}$ cm$^{-3}$, viewed at an angle of $\\sim 20^{\\circ}-40^{\\circ}$ from the jet axis. Using the results of our light curve and spectral modeling, in conjunction with the inference of the circumbinary density, we predict the emergence of late-time radio emission from the deceleration of the kilonova (KN) ejecta on a timescale of $\\sim 5-10$ years that will remain detectable for decades with next-generation radio facilities, making GW\\,170817 a compelling target for long-term radio monitoring.

  9. Creating lenticular galaxies with mergers

    NARCIS (Netherlands)

    Querejeta, Miguel; Eliche-Moral, M. Carmen; Tapia, Trinidad; Borlaff, Alejandro; van de Ven, Glenn; Lyubenova, Mariya; Martig, Marie; Falcón-Barroso, Jesús; Méndez-Abreu, Jairo; Zamorano, Jaime; Gallego, Jesús

    Lenticular galaxies (S0s) represent the majority of early-type galaxies in the local Universe, but their formation channels are still poorly understood. While galaxy mergers are obvious pathways to suppress star formation and increase bulge sizes, the marked parallelism between spiral and lenticular

  10. Mergers + acquisitions.

    Science.gov (United States)

    Hoppszallern, Suzanna

    2002-05-01

    The hospital sector in 2001 led the health care field in mergers and acquisitions. Most deals involved a network augmenting its presence within a specific region or in a market adjacent to its primary service area. Analysts expect M&A activity to increase in 2002.

  11. Mergers & Acquisitions

    DEFF Research Database (Denmark)

    Fomcenco, Alex

    This dissertation is a legal dogmatic thesis, the goal of which is to describe and analyze the current state of law in Europe in regard to some relevant selected elements related to mergers and acquisitions, and the adviser’s counsel in this regard. Having regard to the topic of the dissertation...... and fiscal neutrality, group-related issues, holding-structure issues, employees, stock exchange listing issues, and corporate nationality....

  12. Galaxy mergers

    International Nuclear Information System (INIS)

    Roos, N.

    1981-01-01

    This thesis contains a series of four papers dealing with the effects of interactions among galaxies during the epoch of cluster formation. Galaxy interactions are investigated and the results incorporated in numerical simulations of the formation of groups and clusters of galaxies. The role of galaxy interactions is analysed in the more general context of simulations of an expanding universe. The evolution of galaxies in rich clusters is discussed. The results of the investigations are presented and their relation to other work done in the field are briefly reviewed and an attempt is made to link galaxy mergers to the occurrence of activity in galactic nuclei. (Auth.)

  13. THE POPULATION OF HELIUM-MERGER PROGENITORS: OBSERVATIONAL PREDICTIONS

    International Nuclear Information System (INIS)

    Fryer, Chris L.; Belczynski, Krzysztof; Bulik, Tomasz; Berger, Edo; Thöne, Christina; Ellinger, Carola

    2013-01-01

    The helium-merger gamma-ray burst (GRB) progenitor is produced by the rapid accretion onto a compact remnant (neutron star or black hole) when it undergoes a common envelope inspiral with its companion's helium core. This merger phase produces a very distinct environment around these outbursts and recent observations suggest that, in some cases, we are detecting the signatures of the past merger in the GRB afterglow. These observations allow us, for the first time, to study the specific features of the helium-merger progenitor. In this paper, we couple population synthesis calculations to our current understanding of GRB engines and common envelope evolution to make observational predictions for the helium-merger GRB population. Many mergers do not produce GRB outbursts and we discuss the implications of these mergers with the broader population of astrophysical transients.

  14. Observational evidence for mergers

    International Nuclear Information System (INIS)

    Schweizer, F.

    1983-01-01

    Theory has long suggested that dynamical friction between colliding galaxies must lead to mergers. The problem for observers has been to find which galaxies are mergers. The author first reviews the available evidence for mergers in various kinds of galaxies, then proposes a tentative classification scheme for mergers, and finally discusses mergers in giant ellipticals and their relation to the evolution and perhaps even the formation of ellipticals. (Auth.)

  15. Chandra Observations of Galaxy Zoo Mergers: Frequency of Binary Active Nuclei in Massive Mergers

    Science.gov (United States)

    Teng, Stacy H.; Schawinski, Kevin; Urry, C. Megan; Darg, Dan W.; Kaviraj, Sugata; Oh, Kyuseok; Bonning, Erin W.; Cardamone, Carolin N.; Keel, William C.; Lintott, Chris J.; hide

    2012-01-01

    We present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 1011 M that already have optical AGN signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured (N(sub H) approx merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGN in these mergers are rare (0-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.

  16. MAJOR-MERGER GALAXY PAIRS IN THE COSMOS FIELD—MASS-DEPENDENT MERGER RATE EVOLUTION SINCE z = 1

    International Nuclear Information System (INIS)

    Xu, C. Kevin; Zhao, Yinghe; Gao, Y.; Scoville, N.; Capak, P.; Drory, N.

    2012-01-01

    We present results of a statistical study of the cosmic evolution of the mass-dependent major-merger rate since z = 1. A stellar mass limited sample of close major-merger pairs (the CPAIR sample) was selected from the archive of the COSMOS survey. Pair fractions at different redshifts derived using the CPAIR sample and a local K-band-selected pair sample show no significant variations with stellar mass. The pair fraction exhibits moderately strong cosmic evolution, with the best-fitting function of f pair = 10 –1.88(±0.03) (1 + z) 2.2(±0.2) . The best-fitting function for the merger rate is R mg (Gyr –1 ) = 0.053 × (M star /10 10.7 M ☉ ) 0.3 (1 + z) 2.2 /(1 + z/8). This rate implies that galaxies of M star ∼ 10 10 -10 11.5 M ☉ have undergone ∼0.5-1.5 major mergers since z = 1. Our results show that, for massive galaxies (M star ≥ 10 10.5 M ☉ ) at z ≤ 1, major mergers involving star-forming galaxies (i.e., wet and mixed mergers) can account for the formation of both ellipticals and red quiescent galaxies (RQGs). On the other hand, major mergers cannot be responsible for the formation of most low mass ellipticals and RQGs of M star ∼ 10.3 M ☉ . Our quantitative estimates indicate that major mergers have significant impact on the stellar mass assembly of the most massive galaxies (M star ≥ 10 11.3 M ☉ ), but for less massive galaxies the stellar mass assembly is dominated by the star formation. Comparison with the mass-dependent (ultra)luminous infrared galaxies ((U)LIRG) rates suggests that the frequency of major-merger events is comparable to or higher than that of (U)LIRGs.

  17. Formation of the Small Magellanic Cloud: ancient major merger as a solution to the kinematical differences between old stars and HI gas

    OpenAIRE

    Bekki, Kenji; Chiba, Masashi

    2008-01-01

    Recent observations of the Small Magellanic Cloud (SMC) have revealed that the HI gas shows a significant amount of rotation (V_c 60 km/s), while no or little rotation is evident for the old stellar populations. We suggest that this unique kinematical difference between these components in the SMC can be caused by a major merger event which occurred in the early stage of the SMC formation. Our simulations show that dissipative dwarf-dwarf merging can transform two gas-rich dwarf irregulars in...

  18. Star's death and rebirth. White dwarfs, supernovae, pulsars, black holes

    Energy Technology Data Exchange (ETDEWEB)

    Otzen Petersen, J [Copenhagen Univ. (Denmark)

    1975-01-01

    The evolution of a star from a main sequence star of approximately solar mass, first to a red giant, thereafter to a white dwarf is described in detail. The evolution of more massive stars to supernovae, neutron stars and pulsars is then discussed with special reference to the Crab Nebula. Black holes and X-ray sources are also discussed, in this case with reference to the Cygnus X-1 system. In conclusion, it is pointed out that after their active phase white dwarfs, neutron stars and black holes may exist as dead bodies in space, and only be observeable through their gravitational fields. It is possible that a great number of such bodies may exist, and contribute to the stability of galaxies, also possibly facilitating the explanation of the galaxies' red shifts by means of simple universe models.

  19. Surviving mergers & acquisitions.

    Science.gov (United States)

    Dixon, Diane L

    2002-01-01

    Mergers and acquisitions are never easy to implement. The health care landscape is a minefield of failed mergers and uneasy alliances generating great turmoil and pain. But some mergers have been successful, creating health systems that benefit the communities they serve. Five prominent leaders offer their advice on minimizing the difficulties of M&As.

  20. Mergers and Acquisitions

    OpenAIRE

    Frasch, Manfred; Leptin, Maria

    2000-01-01

    Mergers and acquisitions (M&As) are booming a strategy of choice for organizations attempting to maintain a competitive advantage. Previous research on mergers and acquisitions declares that acquirers do not normally benefit from acquisitions. Targets, on the other hand, have a tendency of gaining positive returns in the few days surrounding merger announcements due to several characteristic on the acquisitions deal. The announcement period wealth effect on acquiring firms, however, is as cle...

  1. Characterizing Black Hole Mergers

    Science.gov (United States)

    Baker, John; Boggs, William Darian; Kelly, Bernard

    2010-01-01

    Binary black hole mergers are a promising source of gravitational waves for interferometric gravitational wave detectors. Recent advances in numerical relativity have revealed the predictions of General Relativity for the strong burst of radiation generated in the final moments of binary coalescence. We explore features in the merger radiation which characterize the final moments of merger and ringdown. Interpreting the waveforms in terms of an rotating implicit radiation source allows a unified phenomenological description of the system from inspiral through ringdown. Common features in the waveforms allow quantitative description of the merger signal which may provide insights for observations large-mass black hole binaries.

  2. On the consequences of low-mass white dwarf mergers

    International Nuclear Information System (INIS)

    Iben, I. Jr.

    1990-01-01

    The theory of binary star evolution suggests that about 10 percent of all main-sequence binary systems should evolve into a close pair of light white dwarfs which merge within a Hubble time. This paper explores the consequences of such mergers on the assumption that a merger can be approximated by a mass-transfer event which occurs on a time scale shorter than that given by the Eddington accretion limit. The evolution of He + He mergers and of CO + He and of hybrid + He mergers are discussed. The birthrate of helium degenerate pairs which merge in less than a Hubble time is estimated, and the space density of low-luminosity merger products currently present in the Galaxy is predicted. It is shown that the evolutionary tracks of models of simulated mergers pass through the region in the H-R diagram occupied by subdwarfs, but that the predicted space density of merger products exceeds by over a factor of three the space density of subdwarf estimated form the known sample of such stars. 61 refs

  3. Simulations of galaxy mergers

    International Nuclear Information System (INIS)

    Villumsen, J.V.

    1982-01-01

    This work is a theoretical investigation of the mechanisms and results of mergers of elliptical galaxies. An N-body code is developed to simulate the dynamics of centrally concentrated collisionless systems. It is used for N-body simulations of the mergers of galaxies with mass ratios of 1:1, 2:1 and 3:1 with a total of 1200 or 2400 particles. The initial galaxies are spherical and non-rotating with Hubble type profiles and isotropic velocity distributions. The remnants are flattened (up to E4) and are oblate, triaxial or prolate depending on the impact parameter. Equal mass mergers are more flattened than unequal mass mergers and have significant velocity anisotropies. The remnants have Hubble type profiles with decreased central surface brightness and increased core radii and tidal radii. In some unequal mass mergers ''isothermal'' haloes tend to form. The density profiles are inconsistent with De Vaucouleurs profiles even though the initial profiles were not. The central velocity dispersion increases in 1:1 and 2:1 mass mergers but decreases in 3:1 mass mergers. Near head-on mergers lead to prolate systems with little rotation while high angular momentum mergers lead to oblate systems with strong rotation. The rotation curves show solid body rotation out to the half mass radius followed by a slow decline. Radial mixing is strong in equal mass mergers where it will weaken radial gradients. In unequal mass mergers there is little radial mixing but matter from the smaller galaxy ends up in the outer parts of the system where it can give rise to colour gradient

  4. INSPIRALLING SUPERMASSIVE BLACK HOLES: A NEW SIGNPOST FOR GALAXY MERGERS

    International Nuclear Information System (INIS)

    Comerford, Julia M.; Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Yan, Renbin; Cooper, Michael C.; Coil, Alison L.; Faber, S. M.; Koo, David C.; Rosario, D. J.; Dutton, Aaron A.

    2009-01-01

    We present a new technique for observationally identifying galaxy mergers spectroscopically rather than through host galaxy imaging. Our technique exploits the dynamics of supermassive black holes (SMBHs) powering active galactic nuclei (AGNs) in merger-remnant galaxies. Because structure in the universe is built up through galaxy mergers and nearly all galaxies host a central SMBH, some galaxies should possess two SMBHs near their centers as the result of a recent merger. These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power AGNs. Using the DEEP2 Galaxy Redshift Survey, we have examined 1881 red galaxies, of which 91 exhibit [O III] and Hβ emission lines indicative of Seyfert 2 activity. Of these, 32 AGNs have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ∼50 km s -1 to ∼300 km s -1 . Two of these AGNs exhibit double-peaked [O III] emission lines, while the remaining 30 AGNs each exhibit a single set of velocity-offset [O III] emission lines. After exploring a variety of physical models for these velocity offsets, we argue that the most likely explanation is inspiralling SMBHs in merger-remnant galaxies. Based on this interpretation, we find that roughly half of the red galaxies hosting AGNs are also merger remnants, which implies that mergers may trigger AGN activity in red galaxies. The AGN velocity offsets we find imply a merger fraction of ∼30% and a merger rate of ∼3 mergers Gyr -1 for red galaxies at redshifts 0.34 < z < 0.82.

  5. ARE ALL SHORT-HARD GAMMA-RAY BURSTS PRODUCED FROM MERGERS OF COMPACT STELLAR OBJECTS?

    International Nuclear Information System (INIS)

    Virgili, Francisco J.; Zhang Bing; O'Brien, Paul; Troja, Eleonora

    2011-01-01

    The origin and progenitors of short-hard gamma-ray bursts (GRBs) remain a puzzle and a highly debated topic. Recent Swift observations suggest that these GRBs may be related to catastrophic explosions in degenerate compact stars, denoted as 'Type I' GRBs. The most popular models include the merger of two compact stellar objects (NS-NS or NS-BH). We utilize a Monte Carlo approach to determine whether a merger progenitor model can self-consistently account for all the observations of short-hard GRBs, including a sample with redshift measurements in the Swift era (z-known sample) and the CGRO/BATSE sample. We apply various merger time delay distributions invoked in compact star merger models to derive the redshift distributions of these Type I GRBs, and then constrain the unknown luminosity function of Type I GRBs using the observed luminosity-redshift (L-z) distributions of the z-known sample. The best luminosity function model, together with the adopted merger delay model, is then applied to confront the peak flux distribution (log N-log P distribution) of the BATSE and Swift samples. We find that for all the merger models invoking a range of merger delay timescales (including those invoking a large fraction of 'prompt mergers'), it is difficult to reconcile the models with all the data. The data are instead statistically consistent with the following two possible scenarios. First, that short/hard GRBs are a superposition of compact-star-merger-origin (Type I) GRBs and a population of GRBs that track the star formation history, which are probably related to the deaths of massive stars (Type II GRBs). Second, the entire short/hard GRB population is consistent with a typical delay of 2 Gyr with respect to the star formation history with modest scatter. This may point toward a different Type I progenitor than the traditional compact star merger models.

  6. Mergers at z = 1

    Science.gov (United States)

    Kao, Lancelot L.

    1993-01-01

    Multiband images of nearby interacting pairs of galaxies, mergers, and normal field galaxies are used to simulate images of high redshift mergers by identifying distinctive morphological features. Preliminary results indicate that it is feasible for the HST to detect these high redshift objects.

  7. Mergers: Success versus failure

    International Nuclear Information System (INIS)

    Carley, G. R.

    1997-01-01

    Successful mergers in the context of long-term value creation, as measured by return realized on investor-provided capital, were discussed. In essence, a successful merger is characterized by being motivated by a sound business reason and strategy for the merger, a reasonable price and sound execution. The acquiror's pre-merger success in managing a company is a good indicator of future success. Poorly managed companies that acquire other companies generally continue to be poorly managed with no significant increase in shareholder value. Prior to the acquisition, identification of the potential target, assessment of the people involved on both sides of the transaction, thorough knowledge of the target's potential for value creation, financial implications (debt, equity, terms and demand, tax implications, the potential effect of the proposed acquisition on the acquiror's business plan) and finally the execution of the process itself, are the important determinants of successful mergers

  8. Mergers and Acquisitions

    DEFF Research Database (Denmark)

    Risberg, Annette

    Introduction to the study of mergers and acquisitions. This book provides an understanding of the mergers and acquisitions process, how and why they occur, and also the broader implications for organizations. It presents issues including motives and planning, partner selection, integration......, employee experiences and communication. Mergers and acquisitions remain one of the most common forms of growth, yet they present considerable challenges for the companies and management involved. The effects on stakeholders, including shareholders, managers and employees, must be considered as well...... by editorial commentaries and reflects the important organizational and behavioural aspects which have often been ignored in the past. By providing this in-depth understanding of the mergers and acquisitions process, the reader understands not only how and why mergers and acquisitions occur, but also...

  9. Predation and Mergers: Is Merger Law Counterproductive?

    OpenAIRE

    Persson, Lars

    1999-01-01

    This Paper shows that predation might help firms overcome the free riding problem of mergers by changing the acquisition situation in the buyer's favour relative to the firms outside the merger. It is also shown that the bidding competition for the prey's assets is most harmful to predators when the use of the prey's assets exerts strong negative externalities on rivals, i.e. when their use severely reduces competitors' profits. The reason is that potential buyers are then willing to pay a hi...

  10. Quantifying the impact of mergers on the angular momentum of simulated galaxies

    Science.gov (United States)

    Lagos, Claudia del P.; Stevens, Adam R. H.; Bower, Richard G.; Davis, Timothy A.; Contreras, Sergio; Padilla, Nelson D.; Obreschkow, Danail; Croton, Darren; Trayford, James W.; Welker, Charlotte; Theuns, Tom

    2018-02-01

    We use EAGLE to quantify the effect galaxy mergers have on the stellar specific angular momentum of galaxies, jstars. We split mergers into dry (gas-poor)/wet (gas-rich), major/minor and different spin alignments and orbital parameters. Wet (dry) mergers have an average neutral gas-to-stellar mass ratio of 1.1 (0.02), while major (minor) mergers are those with stellar mass ratios ≥0.3 (0.1-0.3). We correlate the positions of galaxies in the jstars-stellar mass plane at z = 0 with their merger history, and find that galaxies of low spins suffered dry mergers, while galaxies of normal/high spins suffered predominantly wet mergers, if any. The radial jstars profiles of galaxies that went through dry mergers are deficient by ≈0.3 dex at r ≲ 10 r50 (with r50 being the half-stellar mass radius), compared to galaxies that went through wet mergers. Studying the merger remnants reveals that dry mergers reduce jstars by ≈30 per cent, while wet mergers increase it by ≈10 per cent, on average. The latter is connected to the build-up of the bulge by newly formed stars of high rotational speed. Moving from minor to major mergers accentuates these effects. When the spin vectors of the galaxies prior to the dry merger are misaligned, jstars decreases by a greater magnitude, while in wet mergers corotation and high orbital angular momentum efficiently spun-up galaxies. We predict what would be the observational signatures in the jstars profiles driven by dry mergers: (i) shallow radial profiles and (ii) profiles that rise beyond ≈10 r50, both of which are significantly different from spiral galaxies.

  11. Multiple star formation : chemistry, physics and coevality

    NARCIS (Netherlands)

    Murillo, Mejias N.M.

    2017-01-01

    Multiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary nebulae, to binary black hole mergers. Observations of main sequence stars, young stars and forming

  12. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    Energy Technology Data Exchange (ETDEWEB)

    Deason, Alis [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA (United States); Wetzel, Andrew [TAPIR, California Institute of Technology, Pasadena, CA (United States); Garrison-Kimmel, Shea, E-mail: alis@ucolick.org [Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA (United States)

    2014-10-20

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  13. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    International Nuclear Information System (INIS)

    Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M star > 10 6 M ☉ that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  14. Hospital mergers: a panacea?

    Science.gov (United States)

    Weil, Thomas

    2010-10-01

    Hospital mergers in Europe and North America have been launched to scale down expenditure, enhance the delivery of health care and elevate quality. However, the outcome of mergers suggest that they neither generated cost savings nor improved the quality of care. Almost all consolidations fall short, since those in leadership positions lack the necessary understanding and appreciation of the differences in culture, values and goals of the existing facilities. In spite of these shortcomings, hospital mergers will continue to be pursued in order to improve market share, eliminate excess capacity, gain access to capital and enhance the personal egos of the organizations' leaders.

  15. MERGER ACCOUTING FOR COMPANIES

    Directory of Open Access Journals (Sweden)

    SUCIU GHEORGHE

    2014-05-01

    Full Text Available Companies, especially nowadays, are characterized through great mobility, fast circulation of capital, occurring in their chase for profit. In this context, companies look for alliances, economical and political assistance. These objectives can materialize through merging of companies. The merger can be internal (between Romanian companies or transboundary, which includes foreign companies. In order to correctly reflect these events, the merger operations must be regulated and must respect national and international regulations. One important request concerning the merger operations is that the accounting values of the assets, debts and ownership equity must be brought to the present financial value.

  16. CHANDRA OBSERVATIONS OF GALAXY ZOO MERGERS: FREQUENCY OF BINARY ACTIVE NUCLEI IN MASSIVE MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    Teng, Stacy H. [Observational Cosmology Laboratory, NASA/GSFC, Greenbelt, MD 20771 (United States); Schawinski, Kevin; Urry, C. Megan; Bonning, Erin W. [Department of Physics, Yale University, New Haven, CT 06511 (United States); Darg, Dan W.; Kaviraj, Sugata; Lintott, Chris J. [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Oh, Kyuseok [Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of); Cardamone, Carolin N. [Harriet W. Sheridan Center for Teaching and Learning, Brown University, P.O. Box 1912, Providence, RI 02912 (United States); Keel, William C. [Department of Physics and Astronomy, 206 Gallalee Hall, 514 University Boulevard, University of Alabama, Tuscaloosa, AL 35487-034 (United States); Simmons, Brooke D. [Yale Center for Astronomy and Astrophysics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Treister, Ezequiel, E-mail: stacy.h.teng@nasa.gov [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)

    2012-07-10

    We present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 10{sup 11} M{sub Sun} that already have optical active galactic nucleus (AGN) signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured (N{sub H} {approx}< 1.1 Multiplication-Sign 10{sup 22} cm{sup -2}) X-ray nuclei are relatively common (8/12), but the detections are too faint (<40 counts per nucleus; f{sub 2-10keV} {approx}< 1.2 Multiplication-Sign 10{sup -13} erg s{sup -1} cm{sup -2}) to reliably separate starburst and nuclear activity as the origin of the X-ray emission. Only one merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGNs in these mergers are rare (0%-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.

  17. THE MERGER-TRIGGERED ACTIVE GALACTIC NUCLEUS CONTRIBUTION TO THE ULTRALUMINOUS INFRARED GALAXY POPULATION

    International Nuclear Information System (INIS)

    Draper, A. R.; Ballantyne, D. R.

    2012-01-01

    It has long been thought that there is a connection between ultraluminous infrared galaxies (ULIRGs), quasars, and major mergers. Indeed, simulations show that major mergers are capable of triggering massive starbursts and quasars. However, observations by the Herschel Space Observatory suggest that, at least at high redshift, there may not always be a simple causal connection between ULIRGs and mergers. Here, we combine an evolving merger-triggered active galactic nucleus (AGN) luminosity function with a merger-triggered starburst model to calculate the maximum contribution of major mergers to the ULIRG population. We find that major mergers can account for the entire local population of ULIRGs hosting AGNs and ∼25% of the total local ULIRG luminosity density. By z ∼ 1, major mergers can no longer account for the luminosity density of ULIRGs hosting AGNs and contribute ∼<12% of the total ULIRG luminosity density. This drop is likely due to high-redshift galaxies being more gas rich and therefore able to achieve high star formation rates through secular evolution. Additionally, we find that major mergers can account for the local population of warm ULIRGs. This suggests that selecting high-redshift warm ULIRGs will allow for the identification of high-redshift merger-triggered ULIRGs. As major mergers are likely to trigger very highly obscured AGNs, a significant fraction of the high-redshift warm ULIRG population may host Compton thick AGNs.

  18. Power plays - global mergers

    International Nuclear Information System (INIS)

    Allen, Simon

    1997-01-01

    This article focuses on the increasing number of mergers and acquisitions by electric utilities in the face of growing competition in home markets. The liberalisation of the UK and Scandinavian electricity markets, the impact in Europe of the EU directive on liberalisation, mergers in Switzerland, the selling of Australian generators to UK electric utilities, the globalisation of the industry, and the growing trend for deals between gas and electric utilities are discussed. (UK)

  19. MERGER ACCOUTING FOR COMPANIES

    OpenAIRE

    SUCIU GHEORGHE

    2014-01-01

    Companies, especially nowadays, are characterized through great mobility, fast circulation of capital, occurring in their chase for profit. In this context, companies look for alliances, economical and political assistance. These objectives can materialize through merging of companies. The merger can be internal (between Romanian companies) or transboundary, which includes foreign companies. In order to correctly reflect these events, the merger operations must be regulated and mu...

  20. Simulations of galaxy mergers

    International Nuclear Information System (INIS)

    Villumsen, J.V.; Yale Univ., New Haven, CT

    1982-01-01

    A number of N-body simulations of mergers of equal and unequal galaxies are presented. A new code is presented which determines the potential from a mass distribution by a fourth-order expansion in Tesseral harmonics in three dimensions as an approximation to a collisionless system. The total number of particles in the system is 1200. Two galaxies, each a spherical non-rotating system with isothermal or Hubble density profile, are put in orbit around each other where tidal effects and dynamical friction lead to merging. The final system has a Hubble profile, and in some mergers an 'isothermal' halo forms as found in cD galaxies. Equal mass mergers are more flattened than unequal mass mergers. The central surface brightness decreases except in a merger of isothermal galaxies which shows a major redistribution of energy towards a Hubble profile. Mixing is severe in equal mass mergers, where radial gradients are weakened, while in unequal mass encounters gradients can build up due to less mixing and the formation of a halo. Oblate systems with strong rotation form in high angular momentum encounters while prolate systems with little rotation are formed in near head-on collisions. (author)

  1. Black Hole Mergers and Gravitational Waves: Opening the New Frontier

    Science.gov (United States)

    Centrella, Joan

    2012-01-01

    The final merger of two black holes produces a powerful burst of gravitational waves, emitting more energy than all the stars in the observable universe combined. Since these mergers take place in the regime of strong dynamical gravity, computing the gravitational waveforms requires solving the full Einstein equations of general relativity on a computer. For more than 30 years, scientists tried to simulate these mergers using the methods of numerical relativity. The resulting computer codes were plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. In the past several years, this situation has changed dramatically, with a series of remarkable breakthroughs. This talk will highlight these breakthroughs and the resulting 'gold rush' of new results that is revealing the dynamics of binary black hole mergers, and their applications in gravitational wave detection, testing general relativity, and astrophysics.

  2. Late-stage galaxy mergers in cosmos to z ∼ 1

    International Nuclear Information System (INIS)

    Lackner, C. N.; Silverman, J. D.; Salvato, M.; Kampczyk, P.; Kartaltepe, J. S.; Sanders, D.; Lee, N.; Capak, P.; Scoville, N.; Civano, F.; Halliday, C.; Ilbert, O.; Le Fèvre, O.; Jahnke, K.; Koekemoer, A. M.; Liu, C. T.; Sheth, K.; Toft, S.

    2014-01-01

    The role of major mergers in galaxy and black hole formation is not well-constrained. To help address this, we develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores. The resulting sample of mergers is distinct from those obtained using pair-finding and morphological indicators. Our method relies on median-filtering of high-resolution images to distinguish two concentrated galaxy nuclei at small separations. This method does not rely on low surface brightness features to identify mergers, and is therefore reliable to high redshift. Using mock images, we derive statistical contamination and incompleteness corrections for the fraction of late-stage mergers. The mock images show that our method returns an uncontaminated (<10%) sample of mergers with projected separations between 2.2 and 8 kpc out to z∼1. We apply our new method to a magnitude-limited (m FW 814 <23) sample of 44,164 galaxies from the COSMOS HST/ACS catalog. Using a mass-complete sample with logM ∗ /M ⊙ >10.6 and 0.25mergers. Correcting for incompleteness and contamination, the fractional merger rate increases strongly with redshift as r merge ∝(1+z) 3.8±0.9 , in agreement both with earlier studies and with dark matter halo merger rates. Separating the sample into star-forming and quiescent galaxies shows that the merger rate for star-forming galaxies increases strongly with redshift, (1+z) 4.5±1.3 , while the merger rate for quiescent galaxies is consistent with no evolution, (1+z) 1.1±1.2 . The merger rate also becomes steeper with decreasing stellar mass. Limiting our sample to galaxies with spectroscopic redshifts from zCOSMOS, we find that the star formation rates and X-ray selected active galactic nucleus (AGN) activity in likely late-stage mergers are higher by factors of ∼2 relative to those of a control sample. Combining our sample with more widely separated pairs, we find that 8

  3. Dynamical effects of successive mergers on the evolution of spherical stellar systems

    International Nuclear Information System (INIS)

    Lee, H.M.

    1987-01-01

    Numerical investigations are carried out to study the dynamical effects of high-mass stars formed out of successive mergers among tidally captured binaries on the evolution of spherical stellar systems. It is assumed that all tidally captured systems become mergers in order to maximize these effects. Stellar systems with N greater than about 10 to the 7th are susceptible to merger instability which may lead to the formation of a central black hole. It is shown that globular clusters are likely to achieve postcollapse expansion due to three-body binary heating and stellar evolution, while galactic nuclei can easily be overcome by the merger instability in the core. 25 references

  4. Cosmic Collisions: Galaxy Mergers and Evolution

    Science.gov (United States)

    Trouille, Laura; Willett, Kyle; Masters, Karen; Lintott, Christopher; Whyte, Laura; Lynn, Stuart; Tremonti, Christina A.

    2014-08-01

    Over the years evidence has mounted for a significant mode of galaxy evolution via mergers. This process links gas-rich, spiral galaxies; starbursting galaxies; active galactic nuclei (AGN); post-starburst galaxies; and gas-poor, elliptical galaxies, as objects representing different phases of major galaxy mergers. The post-starburst phase is particularly interesting because nearly every galaxy that evolves from star-forming to quiescent must pass through it. In essence, this phase is a sort of galaxy evolution “bottleneck” that indicates that a galaxy is actively evolving through important physical transitions. In this talk I will present the results from the ‘Galaxy Zoo Quench’ project - using post-starburst galaxies to place observational constraints on the role of mergers and AGN activity in quenching star formation. `Quench’ is the first fully collaborative research project with Zooniverse citizen scientists online; engaging the public in all phases of research, from classification to data analysis and discussion to writing the article and submission to a refereed journal.

  5. SHOCKING TAILS IN THE MAJOR MERGER ABELL 2744

    Energy Technology Data Exchange (ETDEWEB)

    Owers, Matt S.; Couch, Warrick J. [Center for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122 (Australia); Nulsen, Paul E. J.; Randall, Scott W., E-mail: mowers@aao.gov.au [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2012-05-01

    We identify four rare 'jellyfish' galaxies in Hubble Space Telescope imagery of the major merger cluster Abell 2744. These galaxies harbor trails of star-forming knots and filaments which have formed in situ in gas tails stripped from the parent galaxies, indicating they are in the process of being transformed by the environment. Further evidence for rapid transformation in these galaxies comes from their optical spectra, which reveal starburst, poststarburst, and active galactic nucleus features. Most intriguingly, three of the jellyfish galaxies lie near intracluster medium features associated with a merging 'Bullet-like' subcluster and its shock front detected in Chandra X-ray images. We suggest that the high-pressure merger environment may be responsible for the star formation in the gaseous tails. This provides observational evidence for the rapid transformation of galaxies during the violent core passage phase of a major cluster merger.

  6. Anti- versus Pro-Competitive Mergers

    OpenAIRE

    Fridolfsson, Sven-Olof

    2007-01-01

    In a framework where mergers are mutually excluding, I show that firms pursue anti- rather than (alternative) pro-competitive mergers. Potential outsiders to anti-competitive mergers refrain from pursuing pro-competitive mergers if the positive externalities from anti-competitive mergers are strong enough. Potential outsiders to pro-competitive mergers pursue anti-competitive mergers if the negative externalities from the pro-competitive mergers are strong enough. Potential participants in an...

  7. College Mergers: An Emerging Alternative.

    Science.gov (United States)

    Breuder, Robert L.

    1989-01-01

    Examines the merger of Williamsport Area Community College (WACC) and the University of Pennsylvania, necessitated by the city of Williamsport's decision to discontinue its sponsorship of WACC. Considers the principles underlying the merger, legal questions, reactions from within WACC and the surrounding community, and the benefits of the merger.…

  8. Understanding FE Mergers. Research Report

    Science.gov (United States)

    Calvert, Natasha

    2009-01-01

    This report presents research findings and discussion to help develop an understanding of what gives rise to mergers and, when they do happen, what makes them work. The research has focused on merger activity between further education (FE) colleges since incorporation in 1993. Mergers are highly contextual, and part of ensuring success is…

  9. Formation of stars and star clusters in colliding galaxies

    International Nuclear Information System (INIS)

    Belles, Pierre-Emmanuel

    2012-01-01

    Mergers are known to be essential in the formation of large-scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC 7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the HI diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter-Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/HI ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower HI gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/HI ratios higher than in standard HI-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence

  10. THE ELM SURVEY. II. TWELVE BINARY WHITE DWARF MERGER SYSTEMS

    International Nuclear Information System (INIS)

    Kilic, Mukremin; Brown, Warren R.; Kenyon, S. J.; Prieto, Carlos Allende; Agueeros, M. A.; Heinke, Craig

    2011-01-01

    We describe new radial velocity and X-ray observations of extremely low-mass white dwarfs (ELM WDs, ∼0.2 M sun ) in the Sloan Digital Sky Survey Data Release 4 and the MMT Hypervelocity Star survey. We identify four new short period binaries, including two merger systems. These observations bring the total number of short period binary systems identified in our survey to 20. No main-sequence or neutron star companions are visible in the available optical photometry, radio, and X-ray data. Thus, the companions are most likely WDs. Twelve of these systems will merge within a Hubble time due to gravitational wave radiation. We have now tripled the number of known merging WD systems. We discuss the characteristics of this merger sample and potential links to underluminous supernovae, extreme helium stars, AM CVn systems, and other merger products. We provide new observational tests of the WD mass-period distribution and cooling models for ELM WDs. We also find evidence for a new formation channel for single low-mass WDs through binary mergers of two lower mass objects.

  11. DOES M31 RESULT FROM AN ANCIENT MAJOR MERGER?

    International Nuclear Information System (INIS)

    Hammer, F.; Wang, J. L.; Puech, M.; Flores, H.; Fouquet, S.; Yang, Y. B.

    2010-01-01

    The M31 haunted halo is likely associated with a rich merger history, currently assumed to be caused by multiple minor mergers. Here we use the GADGET2 simulation code to test whether M31 could have experienced a major merger in its past history. Our results indicate that a (3 ± 0.5):1 gaseous-rich merger with r pericenter = 25 ± 5 kpc and a polar orbit can explain many properties of M31 and of its halo. The interaction and fusion may have begun 8.75 ± 0.35 and 5.5 ± 0.5 Gyr ago, respectively. Observed fractions of the bulge and the thin and thick disks can be retrieved for a star formation history that is almost quiescent before the fusion. This also accords well with the observed relative fractions of intermediate age and old stars in both the thick disk and the Giant Stream. In this model, the Giant Stream is caused by returning stars from a tidal tail which contains material previously stripped from the satellite prior to the fusion. These returning stars are trapped into elliptical orbits or loops for long periods of time which can reach a Hubble time, and belong to a plane that is 45 0 offset from the M31 disk position angle. Because these streams of stars are permanently fed by new infalling stars with high energy from the tidal tail, we predict large loops which scale rather well with the features recently discovered in the M31 outskirts. We demonstrate that a single merger could explain first-order (intensity and size), morphological, and kinematical properties of the disk, thick disk, bulge, and streams in the halo of M31, as well as the observed distribution of stellar ages, and perhaps metallicities. This challenges the current scenarios assuming that each feature in the disk (the 10 kpc ring) or in its outskirts (thick disk, the Giant Stream, and the numerous streams) is associated with an equivalent number of minor mergers. Given the large number of parameters, further constraints are certainly required to better render the complexity of M31 and

  12. Gravitational waves from neutron stars and asteroseismology

    Science.gov (United States)

    Ho, Wynn C. G.

    2018-05-01

    Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

  13. Internationalize Mergers and Acquisitions

    OpenAIRE

    Zhou, Lili

    2017-01-01

    As globalization processes, an increasing number of companies use mergers and acquisitions as a tool to achieve company growth in the international business world. The purpose of this thesis is to investigate the process of an international M&A and analyze the factors leading to success. The research started with reviewing different academic theory. The important aspects in both pre-M&A phase and post-M&A phase have been studied in depth. Because of the complexity in international...

  14. Mergers & Acquisitions and Intangibles

    OpenAIRE

    Ott, Christian

    2012-01-01

    This dissertation explores the disclosure on intangibles acquired in Mergers & Acquisitos. The related empirical analyses are based on a sample of M&As that are accounted for under the International Financial Reporting Standards (IFRS) and United States Generally Accepted Accounting Principles (US-GAAP). In three different research papers I answer three distinct research questions. In order to enable capital providers and other external stakeholders to evaluate the PPA, the International Fina...

  15. Can galaxy growth be sustained through HI-rich minor mergers?

    Science.gov (United States)

    Lehnert, M. D.; van Driel, W.; Minchin, R.

    2016-05-01

    Local galaxies with specific star-formation rates (star-formation rate per unit mass; sSFR ~ 0.2-10 Gyr-1) that are as high as distant galaxies (z ≈ 1-3), are very rich in Hi. Those with low stellar masses, M⋆ = 108-9 M⊙, for example, have MHI/M⋆ ≈ 5-30. Using continuity arguments, whereby the specific merger rate is hypothesized to be proportional to the specific star-formation rate, along with Hi gas mass measurements for local galaxies with high sSFR, we estimate that moderate-mass galaxies, M⋆ = 109-10.5 M⊙, can acquire enough gas through minor mergers (stellar mass ratios ~4-100) to sustain their star formation rates at z ~ 2. The relative fraction of the gas accreted through minor mergers declines with increasing stellar mass, and for the most massive galaxies considered, M⋆ = 1010.5-11 M⊙, this accretion rate is insufficient to sustain their star formation. We checked our minor merger hypothesis at z = 0 using the same methodology, but now with relations for local normal galaxies, and find that minor mergers cannot account for their specific growth rates, in agreement with observations of Hi-rich satellites around nearby spirals. We discuss a number of attractive features, such as a natural downsizing effect, in using minor mergers with extended Hi disks to support star formation at high redshift. The answer to the question posed by the title, "Can galaxy growth be sustained through Hi-rich minor mergers?", is "maybe", but only for relatively low-mass galaxies and at high redshift.

  16. Constructing and Monitoring the Infrared SED of the First Known Recent Stellar Merger

    Science.gov (United States)

    McCollum, Bruce; Laine, Seppo; Bruhweiler, Frederick; Rottler, Lee

    2012-12-01

    Stellar mergers have long been thought to be astrophysically important to the evolution and global properties of dense stellar aggregates and even open clusters. However, the study of this phenomenon has until now been severely impeded by the lack of any definite, recent merger with which to compare models. It was recently realized that a 2008 nova was in fact a contact binary which erupted when the two stars finally merged. We have obtained post-merger infrared observations which show a large IR excess and a nonstellar SED which have changed subsantially over time, and near-IR emission lines from shocked material. This object is an important opportunity to learn about the nature and time evolution of recent merger products, and to assemble a unique data set which will be used for many years as a basis for modeling stellar mergers.

  17. Observing Galaxy Mergers in Simulations

    Science.gov (United States)

    Snyder, Gregory

    2018-01-01

    I will describe results on mergers and morphology of distant galaxies. By mock-observing 3D cosmological simulations, we aim to contrast theory with data, design better diagnostics of physical processes, and examine unexpected signatures of galaxy formation. Recently, we conducted mock surveys of the Illustris Simulations to learn how mergers would appear in deep HST and JWST surveys. With this approach, we reconciled merger rates estimated using observed close galaxy pairs with intrinsic merger rates predicted by theory. This implies that the merger-pair observability time is probably shorter in the early universe, and therefore that major mergers are more common than implied by the simplest arguments. Further, we show that disturbance-based diagnostics of late-stage mergers can be improved significantly by combining multi-dimensional image information with simulated merger identifications to train automated classifiers. We then apply these classifiers to real measurements from the CANDELS fields, recovering a merger fraction increasing with redshift in broad agreement with pair fractions and simulations, and with statistical errors smaller by a factor of two than classical morphology estimators. This emphasizes the importance of using robust training sets, including cosmological simulations and multidimensional data, for interpreting observed processes in galaxy evolution.

  18. MAJOR GALAXY MERGERS ONLY TRIGGER THE MOST LUMINOUS ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Treister, E.; Schawinski, K.; Urry, C. M.; Simmons, B. D.

    2012-01-01

    Using multiwavelength surveys of active galactic nuclei (AGNs) across a wide range of bolometric luminosities (10 43 bol (erg s –1 ) 46 ) and redshifts (0 bol -f merger relation suggests that downsizing, i.e., the general decline in AGN and star formation activity with decreasing redshift, is driven by a decline in the frequency of major mergers combined with a decrease in the availability of gas at lower redshifts.

  19. The triple-ring nebula around SN 1987A: fingerprint of a binary merger.

    Science.gov (United States)

    Morris, Thomas; Podsiadlowski, Philipp

    2007-02-23

    Supernova 1987A, the first naked-eye supernova observed since Kepler's supernova in 1604, defies a number of theoretical expectations. Its anomalies have long been attributed to a merger between two massive stars that occurred some 20,000 years before the explosion, but so far there has been no conclusive proof that this merger took place. Here, we present three-dimensional hydrodynamical simulations of the mass ejection associated with such a merger and the subsequent evolution of the ejecta, and we show that this accurately reproduces the properties of the triple-ring nebula surrounding the supernova.

  20. EFFICIENT MERGER OF BINARY SUPERMASSIVE BLACK HOLES IN MERGING GALAXIES

    International Nuclear Information System (INIS)

    Khan, Fazeel Mahmood; Just, Andreas; Merritt, David

    2011-01-01

    In spherical galaxies, binary supermassive black holes (SMBHs) have difficulty reaching sub-parsec separations due to depletion of stars on orbits that intersect the massive binary-the 'final parsec problem'. Galaxies that form via major mergers are substantially non-spherical, and it has been argued that the centrophilic orbits in triaxial galaxies might provide stars to the massive binary at a high enough rate to avoid stalling. Here we test that idea by carrying out fully self-consistent merger simulations of galaxies containing central SMBHs. We find hardening rates of the massive binaries that are indeed much higher than in spherical models and essentially independent of the number of particles used in the simulations. Binary eccentricities remain high throughout the simulations. Our results constitute a fully stellar-dynamical solution to the final parsec problem and imply a potentially high rate of events for low-frequency gravitational wave detectors like LISA.

  1. Competition and Mergers among Nonprofits

    NARCIS (Netherlands)

    Prüfer, J.

    2007-01-01

    Should mergers among nonprofit organizations be regulated differently than mergers among for-profit firms? The relevant empirical literature is highly controversial, the theoretical literature is scarce. We analyze the question by modeling duopoly competition with quality-differentiated goods. We

  2. Competition and Mergers among Nonprofits

    NARCIS (Netherlands)

    Prüfer, J.

    2007-01-01

    Should mergers among nonprofit organizations be regulated differently than mergers among for-profit firms? The relevant empirical literature is highly controversial, the theoretical literature is scarce. I analyze the question by modeling duopoly competition with quality-differentiated goods. I

  3. Welfare standards in hospital mergers.

    Science.gov (United States)

    Katona, Katalin; Canoy, Marcel

    2013-08-01

    There is a broad literature on the consequences of applying different welfare standards in merger control. Total welfare is usually defined as the sum of consumer and provider surplus, i.e., potential external effects are not considered. The general result is then that consumer welfare is a more restrictive standard than total welfare, which is advantageous in certain situations. This relationship between the two standards is not necessarily true when the merger has significant external effects. We model mergers on hospital markets and allow for not-profit-maximizing behavior of providers and mandatory health insurance. Mandatory health insurance detaches the financial and consumption side of health care markets, and the concept consumer in merger control becomes non-evident. Patients not visiting the merging hospitals still are affected by price changes through their insurance premiums. External financial effects emerge on not directly affected consumers. We show that applying a restricted interpretation of consumer (neglecting externality) in health care merger control can reverse the relation between the two standards; consumer welfare standard can be weaker than total welfare. Consequently, applying the wrong standard can lead to both clearing socially undesirable and to blocking socially desirable mergers. The possible negative consequences of applying a simple consumer welfare standard in merger control can be even stronger when hospitals maximize quality and put less weight on financial considerations. We also investigate the implications of these results for the practice of merger control.

  4. Knowledge management in international mergers

    NARCIS (Netherlands)

    Grotenhuis, F.D.J.; Weggeman, M.C.D.P.

    2002-01-01

    This paper discusses the need for knowledge management in mergers and acquisitions. In mergers and acquisitions two cultures are combined, and also two systems of knowledge and insights are integrated. In order to develop and sustain competitive advantages for the knowledge-intensive firm, strategic

  5. Indexing mergers and acquisitions

    OpenAIRE

    Gang, Jianhua; Guo, Jie (Michael); Hu, Nan; Li, Xi

    2017-01-01

    We measure the efficiency of mergers and acquisitions by putting forward an index (the ‘M&A Index’) based on stochastic frontier analysis. The M&A Index is calculated for each takeover deal and is standardized between 0 and 1. An acquisition with a higher index encompasses higher efficiency. We find that takeover bids with higher M&A Indices are more likely to succeed. Moreover, the M&A Index shows a strong and positive relation with the acquirers’ post-acquisition stock perfo...

  6. On universality in ergoregion mergers

    International Nuclear Information System (INIS)

    Elvang, Henriette; Figueras, Pau; Hubeny, Veronika E; Rangamani, Mukund; Horowitz, Gary T

    2009-01-01

    We study non-dynamical mergers of ergoregions in d + 1-dimensional vacuum gravity. At the merger point, where the ergosurfaces bounding each ergoregion just touch, solutions exhibit universal behavior when there is rotation only in one plane: the angle between the merging ergosurfaces depends only on the symmetries of the solution, not on any other details of the configuration. We show that universality follows from the fact that the relevant component of Einstein's equation reduces to Laplace's equation at the point of merger. Thus ergoregion mergers mimic mergers of Newtonian equipotentials and have similar universal behavior. For solutions with rotation in more than one plane, universality is lost. We demonstrate universality and non-universality in several explicit examples.

  7. Neutron Stars: Laboratories for Fundamental Physics Under ...

    Indian Academy of Sciences (India)

    DEBADES BANDYOPADHYAY

    2017-09-07

    Sep 7, 2017 ... Abstract. We discuss different exotic phases and components of matter from the crust to the core of neutron stars based on theoretical models for equations of state relevant to core collapse supernova simulations and neutron star merger. Parameters of the models are constrained from laboratory ...

  8. Fossil Hunting: Intracluster Stars in Virgo

    NARCIS (Netherlands)

    Murphy, Eric; Bridge, Carrie; Desai, Vandana; Kenney, Jeffrey; Krick, Jessica; Surace, Jason; van Gorkom, Jacqueline

    2009-01-01

    In dense clusters, galaxy interactions and mergers play a significant role in galaxy evolution. During these interactions, tidal forces can lead to the ejection of stars from their parent galaxies; these stars are a fossil record of environmentally-driven galaxy evolution. We propose to map the

  9. CONNECTIONS BETWEEN GALAXY MERGERS AND STARBURST: EVIDENCE FROM THE LOCAL UNIVERSE

    International Nuclear Information System (INIS)

    Luo, Wentao; Yang, Xiaohu; Zhang, Youcai

    2014-01-01

    Major mergers and interactions between gas-rich galaxies with comparable masses are thought to be the main triggers of starburst. In this work, we study, for a large stellar mass range, the interaction rate of the starburst galaxies in the local universe. We focus independently on central and satellite star forming galaxies extracted from the Sloan Digital Sky Survey. Here the starburst galaxies are selected in the star formation rate (SFR) stellar mass plane with SFRs five times larger than the median value found for ''star forming'' galaxies of the same stellar mass. Through visual inspection of their images together with close companions determined using spectroscopic redshifts, we find that ∼50% of the ''starburst'' populations show evident merger features, i.e., tidal tails, bridges between galaxies, double cores, and close companions. In contrast, in the control sample we selected from the normal star forming galaxies, only ∼19% of galaxies are associated with evident mergers. The interaction rates may increase by ∼5% for the starburst sample and 2% for the control sample if close companions determined using photometric redshifts are considered. The contrast of the merger rate between the two samples strengthens the hypothesis that mergers and interactions are indeed the main causes of starburst

  10. 7 CFR 3575.89 - Mergers.

    Science.gov (United States)

    2010-01-01

    ... merged borrower. Mergers may be approved when: (1) The merger is in the best interest of the Government.... (b) Distinguishing mergers from transfers and assumptions. Mergers occur when one entity combines with another entity in such a way that the first entity ceases to exist as a separate entity while the...

  11. 7 CFR 1779.89 - Mergers.

    Science.gov (United States)

    2010-01-01

    ... of the merged borrower. Mergers may be approved when: (1) The merger is in the best interest of the... borrower. (b) Distinguishing mergers from transfers and assumptions. Mergers occur when one entity combines with another entity in such a way that the first entity ceases to exist as a separate entity while the...

  12. Endogenous mergers: bidder momentum and market reaction

    NARCIS (Netherlands)

    Kling, G.; Weitzel, G.U.

    2010-01-01

    Recent empirical studies on stock misvaluation as a possible determinant of mergers are inconclusive concerning the central hypothesis that over (under) valuation is negatively (positively) associated with merger announcement returns in stock mergers, but not in cash mergers. We provide empirical

  13. Endogenous mergers: Bidder momentum and market reaction

    NARCIS (Netherlands)

    Kling, G.; Weitzel, U.

    Recent empirical studies on stock misvaluation as a possible determinant of mergers are inconclusive concerning the central hypothesis that over(under)valuation is negatively (positively) associated with merger announcement returns in stock mergers, but not in cash mergers. We provide empirical

  14. GRB 080503 LATE AFTERGLOW RE-BRIGHTENING: SIGNATURE OF A MAGNETAR-POWERED MERGER-NOVA

    International Nuclear Information System (INIS)

    Gao, He; Ding, Xuan; Wu, Xue-Feng; Dai, Zi-Gao; Zhang, Bing

    2015-01-01

    GRB 080503 is a short gamma-ray burst (GRB) detected by Swift and has been classified as a GRB originating from a compact star merger. The soft extended emission and the simultaneous late re-brightening in both the X-ray and optical afterglow light curves raise interesting questions regarding its physical origin. We show that the broadband data of GRB 080503 can be well explained within the framework of the double neutron star merger model, provided that the merger remnant is a rapidly rotating massive neutron star with an extremely high magnetic field (i.e., a millisecond magnetar). We show that the late optical re-brightening is consistent with the emission from a magnetar-powered “merger-nova.” This adds one more case to the growing sample of merger-novae associated with short GRBs. The soft extended emission and the late X-ray excess emission are well connected through a magnetar dipole spin-down luminosity evolution function, suggesting that direct magnetic dissipation is the mechanism to produce these X-rays. The X-ray emission initially leaks from a hole in the merger ejecta pierced by the short GRB jet. The hole subsequently closes after the magnetar spins down and the magnetic pressure drops below ram pressure. The X-ray photons are then trapped behind the merger-nova ejecta until the ejecta becomes optically thin at a later time. This explains the essentially simultaneous re-brightening in both the optical and X-ray light curves. Within this model, future gravitational-wave sources could be associated with a bright X-ray counterpart along with the merger-nova, even if the short GRB jet beams away from Earth

  15. arXiv Gravitational Wave Signatures of Highly Compact Boson Star Binaries

    CERN Document Server

    Palenzuela, Carlos; Bezares, Miguel; Cardoso, Vitor; Lehner, Luis; Liebling, Steven

    2017-11-30

    Solitonic boson stars are stable objects made of a complex scalar field with a compactness that can reach values comparable to that of neutron stars. A recent study of the collision of identical boson stars produced only nonrotating boson stars or black holes, suggesting that rotating boson stars may not form from binary mergers. Here we extend this study to include an analysis of the gravitational waves radiated during the coalescence of such a binary, which is crucial to distinguish these events from other binaries with LIGO and Virgo observations. Our studies reveal that the remnant’s gravitational wave signature is mainly governed by its fundamental frequency as it settles down to a nonrotating boson star, emitting significant gravitational radiation during this post-merger state. We calculate how the waveforms and their post-merger frequencies depend on the compactness of the initial boson stars and estimate analytically the amount of energy radiated after the merger.

  16. On the origin of high-velocity runaway stars

    NARCIS (Netherlands)

    Gvaramadze, V.V.; Gualandris, A.; Portegies Zwart, S.

    2009-01-01

    We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50-100 M-circle dot star or a more massive one, formed through runaway mergers of ordinary

  17. Justice Department Airline Merger Policy

    Science.gov (United States)

    Farmer, D. A.

    1972-01-01

    Justice Department airline merger policy is developed within the context of the Federal Aviation Act, in which there is an unusually explicit reliance on competition as a means of fulfilling statutory goals. The economics of the airline industry appear to indicate that low concentration and vigorous competition are particularly viable and desirable. Several factors, including existing regulatory policy, create incentives for airlines to merge whether or not an individual merger promotes or conflicts with the public interest. Specific benefits to the public should be identified and shown to clearly outweight the detriments, including adverse competitive impact, in order for airline mergers to be approved.

  18. SX Phoenicis stars

    International Nuclear Information System (INIS)

    Nemec, J.; Mateo, M.

    1990-01-01

    The purpose of this paper is to review the basic observational information concerning SX Phe stars, including recent findings such as the discovery of about 40 low-luminosity variable stars in the Carina dwarf galaxy and identification of at least one SX Phe star in the metal-rich globular cluster M71. Direct evidence supporting the hypothesis that at least some BSs are binary systems comes from the discovery of two contact binaries and a semidetached binary among the 50 BSs in the globular cluster NGC 5466. Since these systems will coalesce on a time scale 500 Myr, it stands to reason that many (if not most) BSs are coalesced binaries. The merger hypothesis also explains the relatively-large masses (1.0-1.2 solar masses) that have been derived for SX Phe stars and halo BSs, and may also account for the nonvariable BSs in the 'SX Phe instability strip'. 132 refs

  19. THE ELM SURVEY. IV. 24 WHITE DWARF MERGER SYSTEMS

    International Nuclear Information System (INIS)

    Kilic, Mukremin; Brown, Warren R.; Kenyon, S. J.; Allende Prieto, Carlos; Heinke, Craig O.; Agüeros, M. A.; Kleinman, S. J.

    2012-01-01

    We present new radial velocity and X-ray observations of extremely low mass (ELM, ∼0.2 M ☉ ) white dwarf (WD) candidates in the Sloan Digital Sky Survey Data Release 7 area. We identify seven new binary systems with 1-18 hr orbital periods. Five of the systems will merge due to gravitational wave radiation within 10 Gyr, bringing the total number of merger systems found in the ELM Survey to 24. The ELM Survey has now quintupled the known merger WD population. It has also discovered the eight shortest period detached binary WD systems currently known. We discuss the characteristics of the merger and non-merger systems observed in the ELM Survey, including their future evolution. About half of the systems have extreme mass ratios. These are the progenitors of the AM Canum Venaticorum systems and Type Ia supernovae. The remaining targets will lead to the formation of extreme helium stars, subdwarfs, or massive WDs. We identify three targets that are excellent gravitational wave sources. These should be detected by the Laser Interferometer Space Antenna like missions within the first year of operation. The remaining targets are important indicators of what the Galactic foreground may look like for gravitational wave observatories.

  20. Astrophysical Implications of the Binary Black Hole Merger GW150914

    Science.gov (United States)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; hide

    2016-01-01

    The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that in spiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively heavy BHs (> or approx. 25 Stellar Mass) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 12 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (> or approx. 1/cu Gpc/yr) from both types of formation models. The low measured redshift (z approx. = 0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.

  1. Exploring the cosmic evolution of habitability with galaxy merger trees

    Science.gov (United States)

    Stanway, E. R.; Hoskin, M. J.; Lane, M. A.; Brown, G. C.; Childs, H. J. T.; Greis, S. M. L.; Levan, A. J.

    2018-04-01

    We combine inferred galaxy properties from a semi-analytic galaxy evolution model incorporating dark matter halo merger trees with new estimates of supernova and gamma-ray burst rates as a function of metallicity from stellar population synthesis models incorporating binary interactions. We use these to explore the stellar-mass fraction of galaxies irradiated by energetic astrophysical transients and its evolution over cosmic time, and thus the fraction which is potentially habitable by life like our own. We find that 18 per cent of the stellar mass in the Universe is likely to have been irradiated within the last 260 Myr, with GRBs dominating that fraction. We do not see a strong dependence of irradiated stellar-mass fraction on stellar mass or richness of the galaxy environment. We consider a representative merger tree as a Local Group analogue, and find that there are galaxies at all masses which have retained a high habitable fraction (>40 per cent) over the last 6 Gyr, but also that there are galaxies at all masses where the merger history and associated star formation have rendered galaxies effectively uninhabitable. This illustrates the need to consider detailed merger trees when evaluating the cosmic evolution of habitability.

  2. THE ELM SURVEY. IV. 24 WHITE DWARF MERGER SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Kilic, Mukremin [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Brown, Warren R.; Kenyon, S. J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Allende Prieto, Carlos [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain); Heinke, Craig O. [Department of Physics, CCIS 4-183, University of Alberta, Edmonton, AB, T6G 2E1 (Canada); Agueeros, M. A. [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Kleinman, S. J., E-mail: kilic@ou.edu [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States)

    2012-06-01

    We present new radial velocity and X-ray observations of extremely low mass (ELM, {approx}0.2 M{sub Sun }) white dwarf (WD) candidates in the Sloan Digital Sky Survey Data Release 7 area. We identify seven new binary systems with 1-18 hr orbital periods. Five of the systems will merge due to gravitational wave radiation within 10 Gyr, bringing the total number of merger systems found in the ELM Survey to 24. The ELM Survey has now quintupled the known merger WD population. It has also discovered the eight shortest period detached binary WD systems currently known. We discuss the characteristics of the merger and non-merger systems observed in the ELM Survey, including their future evolution. About half of the systems have extreme mass ratios. These are the progenitors of the AM Canum Venaticorum systems and Type Ia supernovae. The remaining targets will lead to the formation of extreme helium stars, subdwarfs, or massive WDs. We identify three targets that are excellent gravitational wave sources. These should be detected by the Laser Interferometer Space Antenna like missions within the first year of operation. The remaining targets are important indicators of what the Galactic foreground may look like for gravitational wave observatories.

  3. PAIRING OF SUPERMASSIVE BLACK HOLES IN UNEQUAL-MASS GALAXY MERGERS

    International Nuclear Information System (INIS)

    Callegari, Simone; Mayer, Lucio; Kazantzidis, Stelios; Colpi, Monica; Governato, Fabio; Quinn, Thomas; Wadsley, James

    2009-01-01

    We examine the pairing process of supermassive black holes (SMBHs) down to scales of 20-100 pc using a set of N-body/SPH simulations of binary mergers of disk galaxies with mass ratios of 1:4 and 1:10. Our numerical experiments are designed to represent merger events occurring at various cosmic epochs. The initial conditions of the encounters are consistent with the ΛCDM paradigm of structure formation, and the simulations include the effects of radiative cooling, star formation (SF), and supernovae feedback. We find that the pairing of SMBHs depends sensitively on the amount of baryonic mass preserved in the center of the companion galaxies during the last phases of the merger. In particular, due to the combination of gasdynamics and SF, we find that a pair of SMBHs can form efficiently in 1:10 minor mergers, provided that galaxies are relatively gas-rich (gas fractions of 30% of the disk mass) and that the mergers occur at relatively high redshift (z ∼ 3), when dynamical friction timescales are shorter. Since 1:10 mergers are most common events during the assembly of galaxies, and mergers are more frequent at high redshift when galaxies are also more gas-rich, our results have positive implications for future gravitational wave experiments such as the Laser Interferometer Space Antenna.

  4. Gas-Rich Mergers in LCDM: Disk Survivability and the Baryonic Assembly of Galaxies

    International Nuclear Information System (INIS)

    Stewart, K.

    2009-01-01

    We use N-body simulations and observationally-normalized relations between dark matter halo mass, stellar mass, and cold gas mass to derive robust expectations about the baryonic content of major mergers out to redshift z ∼ 2. First, we find that the majority of major mergers (m/M > 0.3) experienced by Milky Way size dark matter halos should have been gas-rich, and that gas-rich mergers are increasingly common at high redshift. Though the frequency of major mergers into galaxy halos in our simulations greatly exceeds the observed late-type galaxy fraction, the frequency of gas-poor major mergers is consistent with the observed fraction of bulge-dominated galaxies across the halo mass range M DM ∼ 10 11 - 10 13 M · . These results lend support to the conjecture that mergers with high baryonic gas fractions play an important role in building and/or preserving disk galaxies in the universe. Secondly, we find that there is a transition mass below which a galaxy's past major mergers were primarily gas-rich and above which they were gas poor. The associated stellar mass scale corresponds closely to that marking the observed bimodal division between blue, star-forming, disk-dominated systems and red, bulge-dominated systems with old populations. Finally, we find that the overall fraction of a galaxy's cold baryons deposited directly via major mergers is substantial. Approximately 30% of the cold baryonic material in M star ∼ 10 10 M · (M DM ∼ 10 11.5 M · ) galaxies is accreted as cold gas in major mergers. For more massive galaxies with M star ∼ 10 11 M · (M DM ∼ 10 13 M · the fraction of baryons amassed in mergers is even higher, ∼ 50%, but most of these accreted baryons are delivered directly in the form of stars. This baryonic mass deposition is almost unavoidable, and provides a limit on the fraction of a galaxy's cold baryons that can originate in cold flows or from hot halo cooling

  5. Gas-Rich Mergers in LCDM: Disk Survivability and the Baryonic Assembly of Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Kyle R.; Bullock, James S.; /UC, Irvine; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC; Maller, Ariyeh H.; /New York City Coll. Tech.

    2009-08-03

    We use N-body simulations and observationally-normalized relations between dark matter halo mass, stellar mass, and cold gas mass to derive robust expectations about the baryonic content of major mergers out to redshift z {approx} 2. First, we find that the majority of major mergers (m/M > 0.3) experienced by Milky Way size dark matter halos should have been gas-rich, and that gas-rich mergers are increasingly common at high redshift. Though the frequency of major mergers into galaxy halos in our simulations greatly exceeds the observed late-type galaxy fraction, the frequency of gas-poor major mergers is consistent with the observed fraction of bulge-dominated galaxies across the halo mass range M{sub DM} {approx} 10{sup 11} - 10{sup 13} M{sub {circle_dot}}. These results lend support to the conjecture that mergers with high baryonic gas fractions play an important role in building and/or preserving disk galaxies in the universe. Secondly, we find that there is a transition mass below which a galaxy's past major mergers were primarily gas-rich and above which they were gas poor. The associated stellar mass scale corresponds closely to that marking the observed bimodal division between blue, star-forming, disk-dominated systems and red, bulge-dominated systems with old populations. Finally, we find that the overall fraction of a galaxy's cold baryons deposited directly via major mergers is substantial. Approximately 30% of the cold baryonic material in M{sub star} {approx} 10{sup 10} M{sub {circle_dot}} (M{sub DM} {approx} 10{sup 11.5} M{sub {circle_dot}}) galaxies is accreted as cold gas in major mergers. For more massive galaxies with M{sub star} {approx} 10{sup 11} M{sub {circle_dot}} (M{sub DM} {approx} 10{sup 13} M{sub {circle_dot}} the fraction of baryons amassed in mergers is even higher, {approx} 50%, but most of these accreted baryons are delivered directly in the form of stars. This baryonic mass deposition is almost unavoidable, and provides a

  6. Major galaxy mergers and the growth of supermassive black holes in quasars.

    Science.gov (United States)

    Treister, Ezequiel; Natarajan, Priyamvada; Sanders, David B; Urry, C Megan; Schawinski, Kevin; Kartaltepe, Jeyhan

    2010-04-30

    Despite observed strong correlations between central supermassive black holes (SMBHs) and star formation in galactic nuclei, uncertainties exist in our understanding of their coupling. We present observations of the ratio of heavily obscured to unobscured quasars as a function of cosmic epoch up to z congruent with 3 and show that a simple physical model describing mergers of massive, gas-rich galaxies matches these observations. In the context of this model, every obscured and unobscured quasar represents two distinct phases that result from a massive galaxy merger event. Much of the mass growth of the SMBH occurs during the heavily obscured phase. These observations provide additional evidence for a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH, and coeval star formation.

  7. Neutron Star Physics and EOS

    Directory of Open Access Journals (Sweden)

    Lattimer James M.

    2016-01-01

    Full Text Available Neutron stars are important because measurement of their masses and radii will determine the dense matter equation of state. They will constrain the nuclear matter symmetry energy, which controls the neutron star matter pressure and the interior composition, and will influence the interpretation of nuclear experiments. Astrophysical observations include pulsar timing, X-ray bursts, quiescent low-mass X-ray binaries, pulse profiles from millisecond pulsars, neutrino observations from gravitational collapse supernovae,and gravitational radiation from compact object mergers. These observations will also constrain the neutron star interior, including the properties of superfluidity there, and determine the existence of a possible QCD phase transition.

  8. Trade Union Mergers: A Survey of the Literature.

    Science.gov (United States)

    Michelson, Grant

    2000-01-01

    Examines trade union mergers highlighting merger forms, merger motivation, role played by union officers, and merger waves. Discusses the consequences of mergers on members and union performance and concludes that union merger activity has had little impact. (Contains 74 references.) (JOW)

  9. No Assembly Required: Mergers are Mostly Irrelevant for the Growth of Low-mass Dwarf Galaxies

    Science.gov (United States)

    Fitts, Alex; Boylan-Kolchin, Michael; Bullock, James S.; Weisz, Daniel R.; El-Badry, Kareem; Wheeler, Coral; Faucher-Giguère, Claude-André; Quataert, Eliot; Hopkins, Philip F.; Kereš, Dušan; Wetzel, Andrew; Hayward, Christopher C.

    2018-06-01

    We investigate the merger histories of isolated dwarf galaxies based on a suite of 15 high-resolution cosmological zoom-in simulations, all with masses of Mhalo ≈ 1010 M⊙ (and M⋆ ˜ 105 - 107 M⊙) at z = 0, from the Feedback in Realistic Environments (FIRE) project. The stellar populations of these dwarf galaxies at z = 0 are formed essentially entirely "in situ": over 90% of the stellar mass is formed in the main progenitor in all but two cases, and all 15 of the galaxies have >70% of their stellar mass formed in situ. Virtually all galaxy mergers occur prior to z ˜ 3, meaning that accreted stellar populations are ancient. On average, our simulated dwarfs undergo 5 galaxy mergers in their lifetimes, with typical pre-merger galaxy mass ratios that are less than 1:10. This merger frequency is generally comparable to what has been found in dissipationless simulations when coupled with abundance matching. Two of the simulated dwarfs have a luminous satellite companion at z = 0. These ultra-faint dwarfs lie at or below current detectability thresholds but are intriguing targets for next-generation facilities. The small contribution of accreted stars make it extremely difficult to discern the effects of mergers in the vast majority of dwarfs either photometrically or using resolved-star color-magnitude diagrams (CMDs). The important implication for near-field cosmology is that star formation histories of comparably massive galaxies derived from resolved CMDs should trace the build-up of stellar mass in one main system across cosmic time as opposed to reflecting the contributions of many individual star formation histories of merged dwarfs.

  10. Star Formation of Merging Disk Galaxies with AGN Feedback Effects

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jongwon; Smith, Rory; Yi, Sukyoung K., E-mail: jw.park@yonsei.ac.kr [Department of Astronomy and Yonsei University Observatory, Yonsei University, Seoul 03722 (Korea, Republic of)

    2017-08-20

    Using a numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. Using ∼70 simulations, we investigate SF with the AGN effect in mergers with a variety of mass ratios, inclinations, orbits, galaxy structures, and morphologies. Using these merger simulations with AGN feedback, we measure merger-driven SF using the burst efficiency parameter introduced by Cox et al. We confirm previous studies which demonstrated that, in galaxy mergers, AGN suppresses SF more efficiently than in isolated galaxies. However, we also find that the effect of AGNs on SF is larger in major than in minor mergers. In minor merger simulations with different primary bulge-to-total ratios, the effect of bulge fraction on the merger-driven SF decreases due to AGN feedback. We create models of Sa-, Sb-, and Sc-type galaxies and compare their SF properties while undergoing mergers. With the current AGN prescriptions, the difference in merger-driven SF is not as pronounced as in the recent observational study of Kaviraj. We discuss the implications of this discrepancy.

  11. Star Formation of Merging Disk Galaxies with AGN Feedback Effects

    International Nuclear Information System (INIS)

    Park, Jongwon; Smith, Rory; Yi, Sukyoung K.

    2017-01-01

    Using a numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. Using ∼70 simulations, we investigate SF with the AGN effect in mergers with a variety of mass ratios, inclinations, orbits, galaxy structures, and morphologies. Using these merger simulations with AGN feedback, we measure merger-driven SF using the burst efficiency parameter introduced by Cox et al. We confirm previous studies which demonstrated that, in galaxy mergers, AGN suppresses SF more efficiently than in isolated galaxies. However, we also find that the effect of AGNs on SF is larger in major than in minor mergers. In minor merger simulations with different primary bulge-to-total ratios, the effect of bulge fraction on the merger-driven SF decreases due to AGN feedback. We create models of Sa-, Sb-, and Sc-type galaxies and compare their SF properties while undergoing mergers. With the current AGN prescriptions, the difference in merger-driven SF is not as pronounced as in the recent observational study of Kaviraj. We discuss the implications of this discrepancy.

  12. The Merger Paradox and R&D

    OpenAIRE

    MIYAGIWA, Kaz; WAN, Jiangyun(Yunyun)

    2015-01-01

    The merger paradox is revisited in the presence of cost-reducing R&D in Cournot oligopoly. Two cases are found, in which merger is profitable without satisfying the 80-percent threshold requirement of Salant et al (1983).

  13. University Mergers in Finland: Mediating Global Competition

    Science.gov (United States)

    Välimaa, Jussi; Aittola, Helena; Ursin, Jani

    2014-01-01

    University mergers have become a common strategy for increasing global competitiveness. In this chapter, the authors analyze the implementation of mergers in Finnish universities from the perspective of social justice as conceived within Finland and other Nordic countries.

  14. Mergers, Strategic Investments and Antitrust Policy

    OpenAIRE

    Deneffe, Daniel; Wakker, Peter

    1996-01-01

    textabstractEstablished firms can diversify into new markets in two distinct modes: through internal development or through conglomerate merger. Building on a dynamic three-stage bargaining model with variable threats, this paper shows that a lenient antitrust position toward horizontal mergers can induce established firms that would otherwise not have entered to enter via conglomerate merger. The vigor of antitrust enforcement toward horizontal mergers also affects the conglomerate acquisiti...

  15. The economic impact of merger control legislation

    OpenAIRE

    Carletti, Elena; Hartmann, Philipp; Onega, Steven

    2007-01-01

    We construct a unique dataset of legislative reforms in merger control legislation that occurred in nineteen industrial countries in the period 1987-2004, and investigate the economic impact of these changes on stock prices. In line with the hypothesis that merger control should challenge anticompetitive mergers and thus limit future monopolistic profits, we find that the strengthening of merger control decreases the stock prices of non-financial firms. In contrast, we find that bank stock pr...

  16. DARK MATTER HALO MERGERS: DEPENDENCE ON ENVIRONMENT

    International Nuclear Information System (INIS)

    Hester, J. A.; Tasitsiomi, A.

    2010-01-01

    This paper presents a study of the specific major merger rate as a function of group membership, local environment, and redshift in a very large, 500 h -1 Mpc, cosmological N-body simulation, the Millennium Simulation. The goal is to provide environmental diagnostics of major merger populations in order to test simulations against observations and provide further constraints on major merger driven galaxy evolution scenarios. A halo sample is defined using the maximum circular velocity, which is both well defined for subhalos and closely correlated with galaxy luminosity. Subhalos, including the precursors of major mergers, are severely tidally stripped. Major mergers between subhalos are therefore rare compared to mergers between subhalos and their host halos. Tidal stripping also suppresses dynamical friction, resulting in long major merger timescales when the more massive merger progenitor does not host other subhalos. When other subhalos are present, however, major merger timescales are several times shorter. This enhancement may be due to inelastic unbound collisions between subhalos, which deplete their orbital angular momentum and lead to faster orbital decay. Following these results, we predict that major mergers in group environments are dominated by mergers involving the central galaxy, that the specific major merger rate is suppressed in groups when all group members are considered together, and that the frequency of fainter companions is enhanced for major mergers and their remnants. We also measure an 'assembly bias' in the specific major merger rate in that major mergers of galaxy-like halos are slightly suppressed in overdense environments while major mergers of group-like halos are slightly enhanced. A dynamical explanation for this trend is advanced which calls on both tidal effects and interactions between bound halos beyond the virial radii of locally dynamically dominant halos.

  17. Bundling and mergers in energy markets

    International Nuclear Information System (INIS)

    Granier, Laurent; Podesta, Marion

    2010-01-01

    Does bundling trigger mergers in energy industries? We observe mergers between firms belonging to various energy markets, for instance between gas and electricity providers. These mergers enable firms to bundle. We consider two horizontally differentiated markets. In this framework, we show that bundling strategies in energy markets create incentives to form multi-market firms in order to supply bi-energy packages. Moreover, we find that this type of merger is detrimental to social welfare. (author)

  18. Relativistic simulations of compact object mergers for nucleonic matter and strange quark matter

    Energy Technology Data Exchange (ETDEWEB)

    Bauswein, Andreas Ottmar

    2010-01-29

    Under the assumption that the energy of the ground state of 3-flavor quark matter is lower than the one of nucleonic matter, the compact stellar remnants of supernova explosions are composed of this quark matter. Because of the appearance of strange quarks, such objects are called strange stars. Considering their observational features, strange stars are very similar to neutron stars made of nucleonic matter, and therefore observations cannot exclude the existence of strange stars. This thesis introduces a new method for simulating mergers of compact stars and black holes within a general relativistic framework. The main goal of the present work is the investigation of the question, whether the coalescence of two strange stars in a binary system yields observational signatures that allow one to distinguish them from colliding neutron stars. In this context the gravitational-wave signals are analyzed. It is found that in general the characteristic frequencies in the gravitational-wave spectra are higher for strange stars. Moreover, the amount of matter that becomes gravitationally unbound during the merging is determined. The detection of ejecta of strange star mergers as potential component of cosmic ray flux could serve as a proof of the existence of strange quark matter. (orig.)

  19. Relativistic simulations of compact object mergers for nucleonic matter and strange quark matter

    International Nuclear Information System (INIS)

    Bauswein, Andreas Ottmar

    2010-01-01

    Under the assumption that the energy of the ground state of 3-flavor quark matter is lower than the one of nucleonic matter, the compact stellar remnants of supernova explosions are composed of this quark matter. Because of the appearance of strange quarks, such objects are called strange stars. Considering their observational features, strange stars are very similar to neutron stars made of nucleonic matter, and therefore observations cannot exclude the existence of strange stars. This thesis introduces a new method for simulating mergers of compact stars and black holes within a general relativistic framework. The main goal of the present work is the investigation of the question, whether the coalescence of two strange stars in a binary system yields observational signatures that allow one to distinguish them from colliding neutron stars. In this context the gravitational-wave signals are analyzed. It is found that in general the characteristic frequencies in the gravitational-wave spectra are higher for strange stars. Moreover, the amount of matter that becomes gravitationally unbound during the merging is determined. The detection of ejecta of strange star mergers as potential component of cosmic ray flux could serve as a proof of the existence of strange quark matter. (orig.)

  20. THE CFHTLS-DEEP CATALOG OF INTERACTING GALAXIES. I. MERGER RATE EVOLUTION TO z = 1.2

    International Nuclear Information System (INIS)

    Bridge, C. R.; Carlberg, R. G.; Sullivan, M.

    2010-01-01

    We present the rest-frame optical galaxy merger fraction between 0.2 vega ≤ 22.2 (∼27,000 galaxies) over 2 square degrees, we have compiled the CFHTLS-Deep Catalog of Interacting Galaxies, with ∼ 1600 merging galaxies. We find the merger fraction to be 4.3% ± 0.3% at z ∼ 0.3 and 19.0% ± 2.5% at z ∼ 1, implying evolution of the merger fraction going as (1 + z) m , with m = 2.25 ± 0.24. This result is inconsistent with a mild or non-evolving (m 4σ level of confidence. A mild trend, where by massive galaxies with M * >10 10.7 M sun are undergoing fewer mergers than less massive systems (M * ∼ 10 10 M sun ), consistent with the expectations of galaxy assembly downsizing is observed. Our results also show that interacting galaxies have on average SFRs double that found in non-interacting field galaxies. We conclude that (1) the optical galaxy merger fraction does evolve with redshift, (2) the merger fraction depends mildly on stellar mass, with lower mass galaxies having higher merger fractions at z < 1, and (3) star formation is triggered at all phases of a merger, with larger enhancements at later stages, consistent with N-body simulations.

  1. Assessment of Innovation Effects of Mergers

    OpenAIRE

    Kern, Benjamin René

    2015-01-01

    Summary of Doctoral Dissertation Assessment of Innovation Effects of Mergers The adequate consideration of innovation effects of mergers in merger review was, and still is, one of the most controversially discussed issues between antitrust scholars. In this connection the question has been raised whether the traditional categories in competition law are sufficiently suitable for dealing with innovation aspects or whether new ...

  2. Nurse Executive Leadership During Organizational Mergers.

    Science.gov (United States)

    Piper, Letty Roth; Schneider, Maureen

    2015-12-01

    The recent growth in hospital mergers and the resultant mergers of nursing service departments (NSDs) have produced a need for chief nursing officers (CNOs) to be aware of implications and anticipated dynamic changes. This article addresses the major issues raised by mergers for NSDs and presents an operational step-by-step checklist for CNOs.

  3. 12 CFR 708b.101 - Mergers generally.

    Science.gov (United States)

    2010-01-01

    ... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Mergers generally. 708b.101 Section 708b.101 Banks and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS MERGERS OF FEDERALLY-INSURED CREDIT UNIONS; VOLUNTARY TERMINATION OR CONVERSION OF INSURED STATUS Mergers § 708b.101...

  4. Is Education Getting Lost in University Mergers?

    Science.gov (United States)

    Ursin, Jani; Aittola, Helena; Henderson, Charles; Valimaa, Jussi

    2010-01-01

    Mergers are common phenomena in higher education institutions. Improving educational quality is typically one of the stated goals of university mergers. Yet, little information exists about how merging institutions approach this goal. This paper presents results from a study of planning documents created prior to four mergers in the Finnish higher…

  5. Accounting for distress in bank mergers

    NARCIS (Netherlands)

    Koetter, M.; Bos, J. W. B.; Heid, F.; Kolari, J. W.; Kool, C. J. M.; Porath, D.

    2007-01-01

    Most bank merger studies do not control for hidden bailouts, which may lead to biased results. In this study we employ a unique data set of approximately 1000 mergers to analyze the determinants of bank mergers. We use undisclosed information on banks' regulatory intervention history to distinguish

  6. Neutron stars

    International Nuclear Information System (INIS)

    Irvine, J.M.

    1978-01-01

    The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

  7. Mergers in European Higher Education

    DEFF Research Database (Denmark)

    Rocha, Vera; Teixeira, Pedro N.; Biscaia, Ricardo

    2018-01-01

    In recent years, mergers have been widely used in higher education (HE) to achieve a variety of purposes, ranging from problems of institutional fragmentation to the lack of financial and academic viability, and low institutional efficiency and quality. However, despite a large stream of HE...... literature addressing those issues, there has been little attention to the link between funding-related problems and merger processes. Moreover, there is very little comparative research among different higher education systems experiencing those processes. In this paper, we map and characterize the recent...

  8. Mergers and Acquisitions in India

    OpenAIRE

    Agarwal, Ankita

    2009-01-01

    From the past few decades, Mergers and Acquisitions (M&A) have dominated the environment in which the companies operate. Whenever there is an announcement about a merger, there is an excitement and expectation among the shareholders. This expectation may or may not convert into an abnormal return. It is useful to have some kind of research activity on the performance of M&A, as both bidders and target firms will gain from it. The results have revealed that on average, the returns to the targ...

  9. Recent star formation in interacting galaxies

    International Nuclear Information System (INIS)

    Joseph, R.D.; Wright, G.S.

    1985-01-01

    The subset of galaxy-galaxy interactions which have resulted in a merger are, as a class, ultraluminous IR galaxies. Their IR luminosities span a narrow range which overlaps with the most luminous Seyfert galaxies. However, in contrast with Seyfert galaxies, the available optical, IR, and radio properties of mergers show no evidence for a compact non-thermal central source, and are easily understood in terms of a burst of star formation of extraordinary intensity and spatial extent; they are 'super starbursts'. We argue that super starbursts occur in the evolution of most mergers, and discuss the implications of super starbursts for the suggestion that mergers evolve into elliptical galaxies. Finally, we note that merger-induced shocks are likely to leave the gas from both galaxies in dense molecular form which will rapidly cool, collapse, and fragment. Thus a merger might in fact be expected to result in a burst of star formation of exceptional intensity and spatial extent, i.e. a super starburst. (author)

  10. Hot subdwarfs formed from the merger of two He white dwarfs

    Science.gov (United States)

    Schwab, Josiah

    2018-06-01

    We perform stellar evolution calculations of the remnant of the merger of two He white dwarfs (WDs). Our initial conditions are taken from hydrodynamic simulations of double WD mergers and the viscous disc phase that follows. We evolve these objects from shortly after the merger into their core He-burning phase, when they appear as hot subdwarf stars. We use our models to quantify the amount of H that survives the merger, finding that it is difficult for ≳ 10^{-4} M_{⊙} of H to survive, with even less being concentrated in the surface layers of the object. We also study the rotational evolution of these merger remnants. We find that mass-loss over the {˜ } 10^4 yr following the merger can significantly reduce the angular momentum of these objects. As hot subdwarfs, our models have moderate surface rotation velocities of 30-100 km s-1. The properties of our models are not representative of many apparently isolated hot subdwarfs, suggesting that those objects may form via other channels or that our modelling is incomplete. However, a sub-population of hot subdwarfs are moderate-to-rapid rotators and/or have He-rich atmospheres. Our models help to connect the observed properties of these objects to their progenitor systems.

  11. THE ROLE OF MERGERS IN EARLY-TYPE GALAXY EVOLUTION AND BLACK HOLE GROWTH

    International Nuclear Information System (INIS)

    Schawinski, Kevin; Dowlin, Nathan; Urry, C. Megan; Thomas, Daniel; Edmondson, Edward

    2010-01-01

    Models of galaxy formation invoke the major merger of gas-rich progenitor galaxies as the trigger for significant phases of black hole growth and the associated feedback that suppresses star formation to create red spheroidal remnants. However, the observational evidence for the connection between mergers and active galactic nucleus (AGN) phases is not clear. We analyze a sample of low-mass early-type galaxies known to be in the process of migrating from the blue cloud to the red sequence via an AGN phase in the green valley. Using deeper imaging from Sloan Digital Sky Survey Stripe 82, we show that the fraction of objects with major morphological disturbances is high during the early starburst phase, but declines rapidly to the background level seen in quiescent early-type galaxies by the time of substantial AGN radiation several hundred Myr after the starburst. This observation empirically links the AGN activity in low-redshift early-type galaxies to a significant merger event in the recent past. The large time delay between the merger-driven starburst and the peak of AGN activity allows for the merger features to decay to the background and hence may explain the weak link between merger features and AGN activity in the literature.

  12. Evolving R Coronae Borealis Stars with MESA

    Science.gov (United States)

    Clayton, Geoffrey C.; Lauer, Amber; Chatzopoulos, Emmanouil; Frank, Juhan

    2018-01-01

    R Coronae Borealis (RCB) stars form a small class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He white dwarf (WD) binary and a final helium-shell flash. We are using a combination of 3D hydrodynamics codes and the 1D MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code including nucleosynthesis to construct post-merger spherical models based on realistic merger progenitor models and on our hydrodynamical simulations, and then following the evolution into the region of the HR diagram where RCB stars are located. We are investigating nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed.Our MESA modeling consists of two steps: first mimicking the WD merger event using two different techniques, (a) by choosing a very high mass accretion rate with appropriate abundances and (b) by applying "stellar engineering" to an initial CO WD model to account for the newly merged material by applying an entropy adjusting procedure. Second, we follow the post-merger evolution using a large nuclear reaction network including the effects of convective and rotational instabilities to the mixing of material in order to match the observed RCB abundances. MESA follows the evolution of the merger product as it expands and cools to become an RCB star. We then examine the surface abundances and compare them to the observed RCB abundances. We also investigate how long fusion continues in the He shell near the core and how this processed material is mixed up to the surface of the star. We then model the later evolution of RCB stars to determine their likely lifetimes and endpoints when they have returned to

  13. Medical group mergers: strategies for success.

    Science.gov (United States)

    Latham, Will

    2014-01-01

    As consolidation sweeps over the healthcare industry, many medical groups are considering mergers with other groups as an alternative to employment. While mergers are challenging and fraught with risk, an organized approach to the merger process can dramatically increase the odds for success. Merging groups need to consider the benefits they seek from a merger, identify the obstacles that must be overcome to merge, and develop alternatives to overcome those obstacles. This article addresses the benefits to be gained and issues to be addressed, and provides a tested roadmap that has resulted in many successful medical group mergers.

  14. HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS

    International Nuclear Information System (INIS)

    Bournaud, Frederic; Chapon, Damien; Teyssier, Romain; Powell, Leila C.; Duc, Pierre-Alain; Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Contini, Thierry; Epinat, Benoit; Shapiro, Kristen L.

    2011-01-01

    Disk galaxies at high redshift (z ∼ 2) are characterized by high fractions of cold gas, strong turbulence, and giant star-forming clumps. Major mergers of disk galaxies at high redshift should then generally involve such turbulent clumpy disks. Merger simulations, however, model the interstellar medium as a stable, homogeneous, and thermally pressurized medium. We present the first merger simulations with high fractions of cold, turbulent, and clumpy gas. We discuss the major new features of these models compared to models where the gas is artificially stabilized and warmed. Gas turbulence, which is already strong in high-redshift disks, is further enhanced in mergers. Some phases are dispersion dominated, with most of the gas kinetic energy in the form of velocity dispersion and very chaotic velocity fields, unlike merger models using a thermally stabilized gas. These mergers can reach very high star formation rates, and have multi-component gas spectra consistent with SubMillimeter Galaxies. Major mergers with high fractions of cold turbulent gas are also characterized by highly dissipative gas collapse to the center of mass, with the stellar component following in a global contraction. The final galaxies are early type with relatively small radii and high Sersic indices, like high-redshift compact spheroids. The mass fraction in a disk component that survives or re-forms after a merger is severely reduced compared to models with stabilized gas, and the formation of a massive disk component would require significant accretion of external baryons afterwards. Mergers thus appear to destroy extended disks even when the gas fraction is high, and this lends further support to smooth infall as the main formation mechanism for massive disk galaxies.

  15. Essays on mergers and acquisitions

    NARCIS (Netherlands)

    Faelten, A.I.

    2016-01-01

    “Essays on Mergers and Acquisitions" tackles some of the most prominent business challenges related to M&A activity. The Introduction examines the reasons why deals fail through well-known case studies; Chapter 1 presents a new index measuring countries M&A maturity worldwide; Chapter 2 focus on the

  16. More Mergers,More Acquisitions

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    China aims to maintain sound development of the national economy through M&As Anew round of corporate mergers and acquisitions (M&As) is on the way. On September 6, the State Council announced that it would require companies in the automobile, iron and steel, cement, machinery manufacturing, electro- lytic aluminum and rare earth industries to accelerate M&As.

  17. More Mergers,More Acquisitions

    Institute of Scientific and Technical Information of China (English)

    LAN XINZHEN

    2010-01-01

    @@ A new round of corporate mergers and acquisitions(M&As)is on the way.On September 6,the State Council announced that it would require companies in the automobile,iron and steel,cement,machinery manufacturing,electrolytic aluminum and rare earth industries to accelerate M&As.

  18. A method for estimating time-frequency characteristics of compact binary mergers to improve searches for inspiral, merger and ring-down phases separately

    International Nuclear Information System (INIS)

    Hanna, Chad; Megevand, Miguel; Palenzuela, Carlos; Ochsner, Evan

    2009-01-01

    Recent advances in the description of compact binary systems have produced gravitational waveforms that include inspiral, merger and ring-down phases. Comparing results from numerical simulations with those of post-Newtonian, and related, expansions has provided motivation for employing post-Newtonian waveforms in near merger epochs when searching for gravitational waves and has encouraged the development of analytic fits to full numerical waveforms. Until searches employ full waveforms as templates, data analysts can still conduct separate inspiral, merger and ring-down searches. Improved knowledge about the end of the inspiral phase, the beginning of the merger and the ring-down frequencies will increase the efficiency of searches over each phase separately without needing the exact waveform. We will show that knowledge of the final spin, of which there are many theoretical models and analytic fits to simulations, may give an insight into the time-frequency properties of the merger. We also present implications on the ability to probe the tidal disruption of neutron stars through gravitational waves.

  19. SATELLITE DWARF GALAXIES IN A HIERARCHICAL UNIVERSE: THE PREVALENCE OF DWARF-DWARF MAJOR MERGERS

    OpenAIRE

    Deason, A; Wetzel, A; Garrison-Kimmel, S

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ~10% of satellite dwarf galaxies with M_star > 10^6 M_sun that are within the host...

  20. Simulation of merging neutron stars in full general relativity

    International Nuclear Information System (INIS)

    Shibata, M.

    2001-01-01

    We have performed 3D numerical simulations for merger of equal mass binary neutron stars in full general relativity. We adopt a Γ-law equation of state in the form P = (Γ - 1)ρε where P, ρ, ε and Γ are the pressure, rest mass density, specific internal energy, and the adiabatic constant. As initial conditions, we adopt models of irrotational binary neutron stars in a quasiequilibrium state. Simulations have been carried out for a wide range of Γ and compactness of neutron stars, paying particular attention to the final product and gravitational waves. We find that the final product depends sensitively on the initial compactness of the neutron stars: In a merger between sufficiently compact neutron stars, a black hole is formed in a dynamical timescale. As the compactness is decreased, the formation timescale becomes longer and longer. It is also found that a differentially rotating massive neutron star is formed instead of a black hole for less compact binary cases. In the case of black hole formation, the disk mass around the black hole appears to be very small; less than 1% of the total rest mass. It is indicated that waveforms of high-frequency gravitational waves after merger depend strongly on the compactness of neutron stars before the merger. We point out importance of detecting such gravitational waves of high frequency to constrain the maximum allowed mass of neutron stars. (author)

  1. THE DRIVING MECHANISM OF STARBURSTS IN GALAXY MERGERS

    International Nuclear Information System (INIS)

    Teyssier, Romain; Chapon, Damien; Bournaud, Frederic

    2010-01-01

    We present hydrodynamic simulations of a major merger of disk galaxies, and study the interstellar medium (ISM) dynamics and star formation (SF) properties. High spatial and mass resolutions of 12 pc and 4 x 10 4 M sun allow us to resolve cold and turbulent gas clouds embedded in a warmer diffuse phase. We compare lower-resolution models, where the multiphase ISM is not resolved and is modeled as a relatively homogeneous and stable medium. While merger-driven bursts of SF are generally attributed to large-scale gas inflows toward the nuclear regions, we show that once a realistic ISM is resolved, the dominant process is actually gas fragmentation into massive and dense clouds and rapid SF therein. As a consequence, SF is more efficient by a factor of up to ∼10 and is also somewhat more extended, while the gas density probability distribution function rapidly evolves toward very high densities. We thus propose that the actual mechanism of starburst triggering in galaxy collisions can only be captured at high spatial resolution and when the cooling of gas is modeled down to less than 10 3 K. Not only does our model reproduce the properties of the Antennae system, but it also explains the 'starburst mode' recently revealed in high-redshift mergers compared to quiescent disks.

  2. When Worlds Collide: Chandra Observes Titanic Merger

    Science.gov (United States)

    2002-04-01

    NASA's Chandra X-ray Observatory has provided the best X-ray image yet of two Milky Way-like galaxies in the midst of a head-on collision. Since all galaxies - including our own - may have undergone mergers, this provides insight into how the universe came to look as it does today. Astronomers believe the mega-merger in the galaxy known as Arp 220 triggered the formation of huge numbers of new stars, sent shock waves rumbling through intergalactic space, and could possibly lead to the formation of a supermassive black hole in the center of the new conglomerate galaxy. The Chandra data also suggest that merger of these two galaxies began only 10 million years ago, a short time in astronomical terms. "The Chandra observations show that things really get messed up when two galaxies run into each other at full speed," said David Clements of the Imperial College, London, one of the team members involved in the study. "The event affects everything from the formation of massive black holes to the dispersal of heavy elements into the universe." Arp 220 is considered to be a prototype for understanding what conditions were like in the early universe, when massive galaxies and supermassive black holes were presumably formed by numerous galaxy collisions. At a relatively nearby distance of about 250 million light years, Arp 220 is the closest example of an "ultra-luminous" galaxy, one that gives off a trillion times as much radiation as our Sun. The Chandra image shows a bright central region at the waist of a glowing, hour-glass-shaped cloud of multimillion-degree gas. Rushing out of the galaxy at hundreds of thousands of miles per hour, the super-heated as forms a "superwind," thought to be due to explosive activity generated by the formation of hundreds of millions of new stars. Farther out, spanning a distance of 75,000 light years, are giant lobes of hot gas that could be galactic remnants flung into intergalactic space by the early impact of the collision. Whether the

  3. Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

    Energy Technology Data Exchange (ETDEWEB)

    Antonini, Fabio [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astrophysics, Northwestern University, Evanston, IL 60208 (United States); Toonen, Silvia [Astronomical Institute Anton Pannekoek, University of Amsterdam, P.O. Box 94249, 1090 GE, Amsterdam (Netherlands); Hamers, Adrian S. [Institute for Advanced Study, School of Natural Sciences, Einstein Drive, Princeton, NJ 08540 (United States)

    2017-06-01

    We consider the formation of binary black hole (BH) mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a BH binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov–Kozai cycles) with stellar evolution. After a BH triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. Most BH mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a BH merger rate in the range (0.3–1.3) Gpc{sup −3} yr{sup −1}, or up to ≈2.5 Gpc{sup −3} yr{sup −1} if the BH orbital planes have initially random orientation. Finally, we show that BH mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ≈10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.

  4. VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Lemasle, B.; de Boer, T.J.L.; Hill, V.; Tolstoy, E.; Irwin, M.J.; Jablonka, P.; Venn, K.; Battaglia, G.; Starkenburg, E.; Shetrone, M.; Letarte, B.; François, P.; Helmi, A.; Primas, F.; Kaufer, A.; Szeifert, T.

    2014-01-01

    Context. Fornax is one of the most massive dwarf spheroidal galaxies in the Local Group. The Fornax field star population is dominated by intermediate age stars but star formation was going on over almost its entire history. It has been proposed that Fornax experienced a minor merger event. Aims.

  5. Kilonova/Macronova Emission from Compact Binary Mergers

    Directory of Open Access Journals (Sweden)

    Masaomi Tanaka

    2016-01-01

    Full Text Available We review current understanding of kilonova/macronova emission from compact binary mergers (mergers of two neutron stars or a neutron star and a black hole. Kilonova/macronova is emission powered by radioactive decays of r-process nuclei and it is one of the most promising electromagnetic counterparts of gravitational wave sources. Emission from the dynamical ejecta of ~0.01M⊙ is likely to have a luminosity of ~1040–1041 erg s−1 with a characteristic timescale of about 1 week. The spectral peak is located in red optical or near-infrared wavelengths. A subsequent accretion disk wind may provide an additional luminosity or an earlier/bluer emission if it is not absorbed by the precedent dynamical ejecta. The detection of near-infrared excess in short GRB 130603B and possible optical excess in GRB 060614 supports the concept of the kilonova/macronova scenario. At 200 Mpc distance, a typical peak brightness of kilonova/macronova with 0.01M⊙ ejecta is about 22 mag and the emission rapidly fades to >24 mag within ~10 days. Kilonova/macronova candidates can be distinguished from supernovae by (1 the faster time evolution, (2 fainter absolute magnitudes, and (3 redder colors. Since the high expansion velocity (v~0.1–0.2c is a robust outcome of compact binary mergers, the detection of smooth spectra will be the smoking gun to conclusively identify the gravitational wave source.

  6. HI Absorption in Merger Remnants

    Science.gov (United States)

    Teng, Stacy H.; Veileux, Sylvain; Baker, Andrew J.

    2012-01-01

    It has been proposed that ultraluminous infrared galaxies (ULIRGs) pass through a luminous starburst phase, followed by a dust-enshrouded AGN phase, and finally evolve into optically bright "naked" quasars once they shed their gas/dust reservoirs through powerful wind events. We present the results of our recent 21- cm HI survey of 21 merger remnants with the Green Bank Telescope. These remnants were selected from the QUEST (Quasar/ULIRG Evolution Study) sample of ULIRGs and PG quasars; our targets are all bolometrically dominated by AGN and sample all phases of the proposed ULIRG -> IR-excess quasar -> optical quasar sequence. We explore whether there is an evolutionary connection between ULIRGs and quasars by looking for the occurrence of HI absorption tracing neutral gas outflows; our results will allow us to identify where along the sequence the majority of a merger's gas reservoir is expelled.

  7. Mergers as an Omega estimator

    International Nuclear Information System (INIS)

    Carlberg, R.G.

    1990-01-01

    The redshift dependence of the fraction of galaxies which are merging or strongly interacting is a steep function of Omega and depends on the ratio of the cutoff velocity for interactions to the pairwise velocity dispersion. For typical galaxies the merger rate is shown to vary as (1 + z)exp m, where m is about 4.51 (Omega)exp 0.42, for Omega near 1 and a CDM-like cosmology. The index m has a relatively weak dependence on the maximum merger velocity, the mass of the galaxy, and the background cosmology, for small variations around a cosmology with a low redshift, z of about 2, of galaxy formation. Estimates of m from optical and IRAS galaxies have found that m is about 3-4, but with very large uncertainties. If quasar evolution follows the evolution of galaxy merging and m for quasars is greater than 4, then Omega is greater than 0.8. 21 refs

  8. Star Formation in Merging Galaxies Using FIRE

    Science.gov (United States)

    Perez, Adrianna; Hung, Chao-Ling; Naiman, Jill; Moreno, Jorge; Hopkins, Philip

    2018-01-01

    Galaxy interactions and mergers are efficient mechanisms to birth stars at rates that are significantly higher than found in our Milky Way galaxy. The Kennicut-Schmidt (KS) relation is an empirical relationship between the star-forming rate and gas surface densities of galaxies (Schmidt 1959; Kennicutt 1998). Although most galaxies follow the KS relation, the high levels of star formation in galaxy mergers places them outside of this otherwise tight relationship. The goal of this research is to analyze the gas content and star formation of simulated merging galaxies. Our work utilizes the Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high-resolution cosmological simulation that resolves star-forming regions and incorporates stellar feedback in a physically realistic way. In this work, we have noticed a significant increase in the star formation rate at first and second passage, when the two black holes of each galaxy approach one other. Next, we will analyze spatially resolved star-forming regions over the course of the interacting system. Then, we can study when and how the rates that gas converts into stars deviate from the standard KS. These analyses will provide important insights into the physical mechanisms that regulate star formation of normal and merging galaxies and valuable theoretical predictions that can be used to compare with current and future observations from ALMA or the James Webb Space Telescope.

  9. The Dynamics and Cold Gas Content of Luminous Infrared Galaxy Mergers in the Local Universe

    Science.gov (United States)

    Privon, G. C.

    2014-08-01

    Luminous Infrared Galaxies (LIRGs; 10^11 ≤ L_IR [8 - 1000 μm]/L_sun systems in the local universe, both in terms of their absolute star formation rates—ten to several hundred times that of ``normal'' galaxies—and their star formation rate densities. Many U/LIRGs are interacting or merging disk galaxies undergoing enhanced star formation and/or nuclear activity, likely triggered as the objects transform into massive S0 and elliptical merger remnants. The LIRG population also contains a significant number of apparently isolated disk galaxies which are undergoing enhanced star formation, providing a window on secular galaxy evolution. This work examines nearby U/LIRGs chosen from the Great Observatories All-sky LIRG Survey (GOALS), an infrared flux and luminosity selected sample. The proximity of these systems enables high spatial resolution study of active galactic nuclei (AGN) and extreme star formation in these objects. New maps of the neutral hydrogen (HI) emission are presented for systems morphologically classified in the optical and mid-infrared as non-merging or pre-merger systems. The results of this study suggests that some infrared-selected galaxies may be minor mergers or interactions which are being viewed so soon after first pass that the stellar disk has not yet been significantly disturbed. Galaxy mergers appear to drive much of the enhanced activity observed in U/LIRGs; understanding the merger state of these systems provides a context for observations of star formation and AGN properties. In order to constrain the merger stage, dynamical models for a sample of nine systems were matched to the observed kinematics and morphology as obtained from optical imaging and interferometric HI maps. The resulting models are used not only to constrain the merger stage, but also the encounter geometry of the precursor. Based on these dynamical models a new merger stage classification is presented, which re-scales objects to a common timeline is used to

  10. The Role Of Mergers In Galaxy Formation And Transformations

    Science.gov (United States)

    Conselice, Christopher J.; Mundy, Carl; Duncan, Kenneth

    2017-06-01

    Baryonic assembly of galaxies is one of the largest questions in extragalactic studies, which relates to many other issues, including environment, feedback, star formation, gas accretion and merging. In fact, all of these processes are related and must be accounted for and understood to paint a full picture of galaxy assembly. Perhaps the most straightforward of these processes to measure are the merging and star formation histories. I will present results of combining in a new reanalysis of the three deepest and large NIR surveys take to date: UDS, Ultra-VISTA and VIDEO as part of the REFINE project. Using consistently measured stellar masses and photometric redshifts for galaxies in these fields up to z =3, I will show how the major and minor merger rate can consistently be measured across these fields. Our new method involves a full use of the PDF for photo-zs and stellar masses. We show how the merger fraction and rate are lower than previous results and the implications for this for other methods of galaxy assembly and feedback mechanisms. Invited Talk presented at the conference Galaxy Evolution Across Time, 12-16 June, Paris, France

  11. Mergers, managerial incentives, and efficiencies

    OpenAIRE

    Jovanovic, Dragan

    2014-01-01

    We analyze the effects of synergies from horizontal mergers in a Cournot oligopoly where principals provide their agents with incentives to cut marginal costs prior to choosing output. We stress that synergies come at a cost which possibly leads to a countervailing incentive effect: The merged firm's principal may be induced to stifle managerial incentives in order to reduce her agency costs. Whenever this incentive effect dominates the well-known direct synergy effect, synergies actually red...

  12. Pre and Post Merger Valuation- A Study of Tata Corus Merger Deal

    OpenAIRE

    Sumeet Gupta

    2009-01-01

    Indian Economy being characterized as Global Economy leading to inorganic growth through Mergers, Acquisitions, Takeovers and Joint Ventures. Mergers would affect the company’s inflow and outflow of various variables like sales, expenses and cash position etc. It becomes imperative to evaluate the pre merger and post merger conditions of the firms so that successful deal can be carried out. The deal would also affect the shareholders wealth. The prediction of future forecasted sales and other...

  13. A NEW STELLAR CHEMO-KINEMATIC RELATION REVEALS THE MERGER HISTORY OF THE MILKY WAY DISK

    Energy Technology Data Exchange (ETDEWEB)

    Minchev, I.; Chiappini, C.; Steinmetz, M.; De Jong, R. S.; Scannapieco, C. [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Martig, M. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia); Boeche, C.; Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Zwitter, T. [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia); Wyse, R. F. G. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Binney, J. J. [Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford OX1 3NP (United Kingdom); Bland-Hawthorn, J. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Bienaymé, O.; Famaey, B. [CNRS, Observatoire Astronomique, Université de Strasbourg, 11 rue de l' Université, F-67000 Strasbourg (France); Freeman, K. C. [Australian National University, Canberra, ACT 0200 (Australia); Gibson, B. K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilmore, G.; Kordopatis, G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Helmi, A. [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands); Lee, Y. S. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); and others

    2014-01-20

    The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine, so a proxy like the abundance of α elements (e.g., Mg) with respect to iron, [α/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the Radial Velocity Experiment survey with high-quality chemical and kinematic information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first gigayear of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early universe, which have affected the outer parts of the disk more strongly, and the subsequent radial migration of stars with cooler kinematics from the inner disk. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disk merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events.

  14. A NEW STELLAR CHEMO-KINEMATIC RELATION REVEALS THE MERGER HISTORY OF THE MILKY WAY DISK

    International Nuclear Information System (INIS)

    Minchev, I.; Chiappini, C.; Steinmetz, M.; De Jong, R. S.; Scannapieco, C.; Martig, M.; Boeche, C.; Grebel, E. K.; Zwitter, T.; Wyse, R. F. G.; Binney, J. J.; Bland-Hawthorn, J.; Bienaymé, O.; Famaey, B.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Kordopatis, G.; Helmi, A.; Lee, Y. S.

    2014-01-01

    The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine, so a proxy like the abundance of α elements (e.g., Mg) with respect to iron, [α/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the Radial Velocity Experiment survey with high-quality chemical and kinematic information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first gigayear of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early universe, which have affected the outer parts of the disk more strongly, and the subsequent radial migration of stars with cooler kinematics from the inner disk. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disk merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events

  15. KINEMATIC CLASSIFICATIONS OF LOCAL INTERACTING GALAXIES: IMPLICATIONS FOR THE MERGER/DISK CLASSIFICATIONS AT HIGH-z

    International Nuclear Information System (INIS)

    Hung, Chao-Ling; Larson, Kirsten L.; Sanders, D. B.; Rich, Jeffrey A.; Yuan, Tiantian; Kewley, Lisa J.; Casey, Caitlin M.; Smith, Howard A.; Hayward, Christopher C.

    2015-01-01

    The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. Galaxy kinematics as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially redshift the Wide Field Spectrograph observations of these local (U)LIRGs to z = 1.5 to make a realistic comparison with observations at high-z, and also to ensure that all galaxies have the same spatial sampling of ∼900 pc. Using both kinemetry-based and visual classifications, we find that the reliability of kinematic classification shows a strong trend with the interaction stage of galaxies. Mergers with two nuclei and tidal tails have the most distinct kinematics compared to isolated disks, whereas a significant population of the interacting disks and merger remnants are indistinguishable from isolated disks. The high fraction of mergers displaying disk-like kinematics reflects the complexity of the dynamics during galaxy interactions. Additional merger indicators such as morphological properties traced by stars or molecular gas are required to further constrain the merger/disk classifications at high-z

  16. Disclosure requirements for merger and acquisition transactions

    International Nuclear Information System (INIS)

    Holm, D.I.

    1998-01-01

    The legal disclosure requirements for merger and acquisition transactions involving Canadian public companies are described. The focus is on issues regarding merger and acquisition related disclosure, including the potential consequences of failing to provide proper information, Ontario Securities Commission Policy 9.1 considerations regarding valuation, review, and approval, cross border considerations and financing a merger and acquisition transaction. Legal and practical consequences for failing to provide proper disclosure, including the steps involved in establishing the due diligence defence, are also discussed

  17. National Versus International Mergers and Trade Liberalization

    OpenAIRE

    Yildiz, Halis Murat

    2003-01-01

    This paper uses an endogenous merger formation approach in a concentrated international oligopoly to examine the effects of trade liberalization on the nature of merger incentives (national vs. international). The effects of unilateral trade liberalization on a country’s industry structure are found to be depending on the other country’s trade policy regime. If the other country practices free trade, unilateral liberalization by a country yields international mergers whereas if it practices a...

  18. Mergers and acquisitions: valuation and risk assessment

    International Nuclear Information System (INIS)

    McVeigh, C.A.

    1996-01-01

    An overview of various aspects of mergers and acquisition transactions in the petroleum industry were presented. Incentives to mergers and acquisitions were reviewed and discussed, among them value opportunity, critical size, incremental tax pools, financial distress, shareholder dissatisfaction, strategic infrastructure position, complementary assets, and undeveloped land inventory. Current trends in mergers and acquisitions were highlighted. An industry checklist for risk assessments discussing financial position, engineering forecasts, and taxation was also included

  19. LEGAL CONSEQUENCES OF MERGERS AND ACQUISITIONS

    Directory of Open Access Journals (Sweden)

    Amelia-Raluca ONIŞOR

    2016-05-01

    Full Text Available The research analyses the legal effects of mergers and acquisitions from the Romanian Company Law perspective, underlining certain general principles, the procedure of annulment of such a legal transformation of companies and the protection of the employees of companies participating in the merger according to the Law no. 67/2006. These consequences of mergers and acquisions are to be seen in the broader light of the most important purpose of this legal instrument, maximizing financial and organizational efficiencies, thus legal certainty is a desirable goal to be assumed by any merger regulation.

  20. MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER?

    International Nuclear Information System (INIS)

    Hopkins, Philip F.; Bundy, Kevin; Wetzel, Andrew; Croton, Darren; Hernquist, Lars; Keres, Dusan; Younger, Joshua D.; Khochfar, Sadegh; Stewart, Kyle

    2010-01-01

    We use a suite of semi-empirical models to predict the galaxy-galaxy merger rate and relative contributions to bulge growth as a function of mass (both halo and stellar), redshift, and mass ratio. The models use empirical constraints on the halo occupation distribution, evolved forward in time, to robustly identify where and when galaxy mergers occur. Together with the results of high-resolution merger simulations, this allows us to quantify the relative contributions of mergers with different properties (e.g., mass ratios, gas fractions, redshifts) to the bulge population. We compare with observational constraints, and find good agreement. We also provide useful fitting functions and make public a code to reproduce the predicted merger rates and contributions to bulge mass growth. We identify several robust conclusions. (1) Major mergers dominate the formation and assembly of ∼L * bulges and the total spheroid mass density, but minor mergers contribute a non-negligible ∼30%. (2) This is mass dependent: bulge formation and assembly is dominated by more minor mergers in lower-mass systems. In higher-mass systems, most bulges originally form in major mergers near ∼L * , but assemble in increasingly minor mergers. (3) The minor/major contribution is also morphology dependent: higher B/T systems preferentially form in more major mergers, with B/T roughly tracing the mass ratio of the largest recent merger; lower B/T systems preferentially form in situ from minor mergers. (4) Low-mass galaxies, being gas-rich, require more mergers to reach the same B/T as high-mass systems. Gas-richness dramatically suppresses the absolute efficiency of bulge formation, but does not strongly influence the relative contribution of major versus minor mergers. (5) Absolute merger rates at fixed mass ratio increase with galaxy mass. (6) Predicted merger rates agree well with those observed in pair and morphology-selected samples, but there is evidence that some morphology

  1. DOUBLE COMPACT OBJECTS. I. THE SIGNIFICANCE OF THE COMMON ENVELOPE ON MERGER RATES

    International Nuclear Information System (INIS)

    Dominik, Michal; Belczynski, Krzysztof; Bulik, Tomasz; Fryer, Christopher; Holz, Daniel E.; Berti, Emanuele; Mandel, Ilya; O'Shaughnessy, Richard

    2012-01-01

    The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from population synthesis models. We compute the Galactic merger rates for NS-NS, BH-NS, and BH-BH mergers with the StarTrack code. The most important revisions include updated wind mass-loss rates (allowing for stellar-mass black holes up to 80 M ☉ ), a realistic treatment of the common envelope phase (a process that can affect merger rates by 2-3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed m ass gap ) . Our findings include the following. (1) The binding energy of the envelope plays a pivotal role in determining whether a binary merges within a Hubble time. (2) Our description of natal kicks from supernovae plays an important role, especially for the formation of BH-BH systems. (3) The masses of BH-BH systems can be substantially increased in the case of low metallicities or weak winds. (4) Certain combinations of parameters underpredict the Galactic NS-NS merger rate and can be ruled out. (5) Models incorporating delayed supernovae do not agree with the observed NS/BH 'mass gap', in accordance with our previous work. This is the first in a series of three papers. The second paper will study the merger rates of double compact objects as a function of redshift, star formation rate, and metallicity. In the third paper, we will present the detection rates for gravitational-wave observatories, using up-to-date signal waveforms and sensitivity curves.

  2. Bright Merger-nova Emission Powered by Magnetic Wind from a Newborn Black Hole

    Science.gov (United States)

    Ma, Shuai-Bing; Lei, Wei-Hua; Gao, He; Xie, Wei; Chen, Wei; Zhang, Bing; Wang, Ding-Xiong

    2018-01-01

    Mergers of neutron star–neutron star (NS–NS) or neutron star–black hole (NS–BH) binaries are candidate sources of gravitational waves (GWs). At least a fraction of the merger remnants should be a stellar mass BH with sub-relativistic ejecta. A collimated jet is launched via the Blandford–Znajek mechanism from the central BH to trigger a short gamma-ray burst (sGRB). At the same time, a near-isotropic wind may be driven by the Blandford–Payne mechanism (BP). In previous work, additional energy injection to the ejecta from the BP mechanism was ignored, and radioactive decay has long been thought to be the main source of the kilonova energy. In this Letter, we propose that the wind driven by the BP mechanism from the newborn BH’s disk can heat up and push the ejecta during the prompt emission phase or even at late times when there is fall-back accretion. Such a BP-powered merger-nova could be bright in the optical band even for a low-luminosity sGRB. The detection of a GW merger event with a BH clearly identified as a remnant, accompanied by a bright merger-nova, would provide robust confirmation of our model.

  3. THE EFFECT OF DRY MERGERS ON THE COLOR-MAGNITUDE RELATION OF EARLY-TYPE GALAXIES

    International Nuclear Information System (INIS)

    Skelton, Rosalind E.; Bell, Eric F.; Somerville, Rachel S.

    2009-01-01

    We investigate the effect of dry merging on the color-magnitude relation (CMR) of galaxies and find that the amount of merging predicted by a hierarchical model results in a red sequence that compares well with the observed low-redshift relation. A sample of ∼ 29,000 early-type galaxies selected from the Sloan Digital Sky Survey Data Release 6 shows that the bright end of the CMR has a shallower slope and smaller scatter than the faint end. This magnitude dependence is predicted by a simple toy model in which gas-rich mergers move galaxies onto a 'creation red sequence' (CRS) by quenching their star formation, and subsequent mergers between red, gas-poor galaxies (so-called 'dry' mergers) move galaxies along the relation. We use galaxy merger trees from a semianalytic model of galaxy formation to test the amplitude of this effect and find a change in slope at the bright end that brackets the observations, using gas fraction thresholds of 10%-30% to separate wet and dry mergers. A more realistic model that includes scatter in the CRS shows that dry merging decreases the scatter at the bright end. Contrary to previous claims, the small scatter in the observed CMR thus cannot be used to constrain the amount of dry merging.

  4. Gravitational waves from neutron stars and asteroseismology.

    Science.gov (United States)

    Ho, Wynn C G

    2018-05-28

    Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'. © 2018 The Author(s).

  5. Symbiotic stars

    International Nuclear Information System (INIS)

    Boyarchuk, A.A.

    1975-01-01

    There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

  6. Mergers, Strategic Investments and Antitrust Policy

    NARCIS (Netherlands)

    D. Deneffe (Daniel); P.P. Wakker (Peter)

    1996-01-01

    textabstractEstablished firms can diversify into new markets in two distinct modes: through internal development or through conglomerate merger. Building on a dynamic three-stage bargaining model with variable threats, this paper shows that a lenient antitrust position toward horizontal mergers can

  7. On Mergers in Consumer Search Markets

    NARCIS (Netherlands)

    M.C.W. Janssen (Maarten); J.L. Moraga-Gonzalez (José Luis)

    2007-01-01

    textabstractWe study mergers in a market where N firms sell a homogeneous good and consumers search sequentially to discover prices. The main motivation for such an analysis is that mergers generally affect market prices and thereby, in a search environment, the search behavior of consumers.

  8. Potential gains from hospital mergers in Denmark.

    Science.gov (United States)

    Kristensen, Troels; Bogetoft, Peter; Pedersen, Kjeld Moeller

    2010-12-01

    The Danish hospital sector faces a major rebuilding program to centralize activity in fewer and larger hospitals. We aim to conduct an efficiency analysis of hospitals and to estimate the potential cost savings from the planned hospital mergers. We use Data Envelopment Analysis (DEA) to estimate a cost frontier. Based on this analysis, we calculate an efficiency score for each hospital and estimate the potential gains from the proposed mergers by comparing individual efficiencies with the efficiency of the combined hospitals. Furthermore, we apply a decomposition algorithm to split merger gains into technical efficiency, size (scale) and harmony (mix) gains. The motivation for this decomposition is that some of the apparent merger gains may actually be available with less than a full-scale merger, e.g., by sharing best practices and reallocating certain resources and tasks. Our results suggest that many hospitals are technically inefficient, and the expected "best practice" hospitals are quite efficient. Also, some mergers do not seem to lower costs. This finding indicates that some merged hospitals become too large and therefore experience diseconomies of scale. Other mergers lead to considerable cost reductions; we find potential gains resulting from learning better practices and the exploitation of economies of scope. To ensure robustness, we conduct a sensitivity analysis using two alternative returns-to-scale assumptions and two alternative estimation approaches. We consistently find potential gains from improving the technical efficiency and the exploitation of economies of scope from mergers.

  9. The University of Johannesburg merger: Academics experience of the pre-merger phase

    Directory of Open Access Journals (Sweden)

    G. A. Goldman

    2006-12-01

    Full Text Available Purpose of the study: The aim of this study is to gain an understanding of the merger experiences academic staff were exposed to during the pre-merger phase of the University of Johannesburg merger. Of particular interest is how these experiences translate into acceptance of the merger amongst academic staff. The study was borne out of the transformation of the higher education landscape in South Africa, which is typified by a spate of mergers between higher education institutions. Design/methodology/approach: As the purpose of the study was, inter alia, aimed at understanding the merger experiences of academic staff, the study was conducted according to an interpretive research paradigm, where interpretation of data calls for an insider perspective, in order to "see things through their eyes" as it were. In this regard, a qualitative methodology was employed. Findings: Findings indicate that academic staff members at the University of Johannesburg experience two distinct mental states during the pre-merger phase. Following the announcement of the merger, reaction and experience tend to be emotionally driven but as merging efforts become more concrete over time, this emotive state is replaced by a more rationally driven disposition. Implications: The distinction between an emotive and rational demeanour during the pre-merger phase of a merger affords managers and leaders the opportunity to plan change interventions in such a way that irrational, emotive responses and behaviour do not hamper progress in terms of merger implementation. In a more general sense, this study highlights the process of transition individual staff members pass through as they have to come to terms with the changes brought about by a merger. Originality / Value: The majority of merger literature, as well as change literature, focuses on the organisational context of change during a merger. Limited literature exists on the personal effects of a change event such as a

  10. Essays on mergers and acquisitions

    OpenAIRE

    Faelten, A.I.

    2016-01-01

    “Essays on Mergers and Acquisitions" tackles some of the most prominent business challenges related to M&A activity. The Introduction examines the reasons why deals fail through well-known case studies; Chapter 1 presents a new index measuring countries M&A maturity worldwide; Chapter 2 focus on the importance of corporate governance when conducting deals in unknown territories; whilst Chapter 3 and 4 conduct research on companies’ decision to tap capital markets and their subsequent M&A acti...

  11. Mergers and integrated care: the Quebec experience.

    Science.gov (United States)

    Demers, Louis

    2013-01-01

    As a researcher, I have studied the efforts to increase the integration of health and social services in Quebec, as well as the mergers in the Quebec healthcare system. These mergers have often been presented as a necessary transition to break down the silos that compartmentalize the services dispensed by various organisations. A review of the studies about mergers and integrated care projects in the Quebec healthcare system, since its inception, show that mergers cannot facilitate integrated care unless they are desired and represent for all of the actors involved an appropriate way to deal with service organisation problems. Otherwise, mergers impede integrated care by creating increased bureaucratisation and standardisation and by triggering conflicts and mistrust among the staff of the merged organisations. It is then preferable to let local actors select the most appropriate organisational integration model for their specific context and offer them resources and incentives to cooperate.

  12. Mergers and integrated care: the Quebec experience

    Directory of Open Access Journals (Sweden)

    Louis Demers

    2013-02-01

    Full Text Available As a researcher, I have studied the efforts to increase the integration of health and social services in Quebec, as well as the mergers in the Quebec healthcare system. These mergers have often been presented as a necessary transition to break down the silos that compartmentalize the services dispensed by various organisations. A review of the studies about mergers and integrated care projects in the Quebec healthcare system, since its inception, show that mergers cannot facilitate integrated care unless they are desired and represent for all of the actors involved an appropriate way to deal with service organisation problems. Otherwise, mergers impede integrated care by creating increased bureaucratisation and standardisation and by triggering conflicts and mistrust among the staff of the merged organisations. It is then preferable to let local actors select the most appropriate organisational integration model for their specific context and offer them resources and incentives to cooperate.

  13. Risks of Mergers and Acquisitions Processes

    Directory of Open Access Journals (Sweden)

    Skitsko Volodymyr I.

    2017-06-01

    Full Text Available Despite structural changes both in the economies of individual countries and in the world at large, the size of the merger/acquisition market is not declining and is tending to grow further. However, uncertainty in the global environment increases the importance of proper analysis, assessment and risk management in merger/acquisition transactions. Using the relevant research and publications by various authors, we have built a general ranking of the significance of merger and acquisition risks according to phases of the indicated process, with comparison of individual risk ratings, based on the publications by authors from Central and Eastern Europe and other countries around the world. The ranking of risks and threats of mergers/acquisitions proposed in this work can be considered one of the most complete for today. Further research needs to focus on the analysis, evaluation, and modeling of merger/acquisition risks, which occupy the top of the ranking, presented by the article.

  14. Impact of bank mergers on shareholders’ wealth

    Directory of Open Access Journals (Sweden)

    Odero Naor Juma

    2013-07-01

    Full Text Available Mergers and acquisitions (M&As perform a vital role in corporate finance in enabling firms achieve varied objectives and financial strategies. This study sought to comprehend the impacts that previous bank mergers have had on the shareholders’ wealth. The study location was in Kenya and it adopted the descriptive survey and correlation design in which the success of mergers was measured based on the objective oriented model using the annual accounts. The study computed the return on assets (ROA, return on equity (ROE and the efficiency ratio (EFF as indicators of shareholder value. The results of the commercial banks were analysed for a five-year period (2006-2010. The study reveals that mergers significantly influence shareholder value with banks that have undertaken mergers creating more value than those that have not. Such banks were ascertained to have posted better results than the overall sector.

  15. THE HALO MERGER RATE IN THE MILLENNIUM SIMULATION AND IMPLICATIONS FOR OBSERVED GALAXY MERGER FRACTIONS

    International Nuclear Information System (INIS)

    Genel, Shy; Genzel, Reinhard; Bouche, Nicolas; Naab, Thorsten; Sternberg, Amiel

    2009-01-01

    We have developed a new method to extract halo merger rates from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the standard friends-of-friends (FOF) halo identification algorithm, we find a lower merger rate compared to previous work. The reductions are more significant at lower redshifts and lower halo masses, and especially for minor mergers. Our new approach results in a better agreement with predictions from the extended Press-Schechter model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ∼20% overestimate of the merger rate. Therefore, we define halo masses by including only particles that are gravitationally bound to their FOF groups. We provide new best-fitting parameters for a global formula to account for these improvements. In addition, we extract the merger rate per progenitor halo, as well as per descendant halo. The merger rate per progenitor halo is the quantity that should be related to observed galaxy merger fractions when they are measured via pair counting. At low-mass/redshift, the merger rate increases moderately with mass and steeply with redshift. At high enough mass/redshift (for the rarest halos with masses a few times the 'knee' of the mass function), these trends break down, and the merger rate per progenitor halo decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos, in addition to the minor and major merger rates. We provide an analytic formula that converts any given merger rate per descendant halo into a merger rate per progenitor halo. Finally, we perform a direct comparison between observed merger fractions and the fraction of halos in the Millennium Simulation that have undergone a major merger during the recent dynamical friction time, and find a

  16. Galaxy Mergers and Dark Matter Halo Mergers in LCDM: Mass, Redshift, and Mass-Ratio Dependence

    International Nuclear Information System (INIS)

    Stewart, K.

    2009-01-01

    We employ a high-resolution LCDM N-body simulation to present merger rate predictions for dark matter halos and investigate how common merger-related observables for galaxies - such as close pair counts, starburst counts, and the morphologically disturbed fraction - likely scale with luminosity, stellar mass, merger mass ratio, and redshift from z = 0 to z = 4. We provide a simple 'universal' fitting formula that describes our derived merger rates for dark matter halos a function of dark halo mass, merger mass ratio, and redshift, and go on to predict galaxy merger rates using number density-matching to associate halos with galaxies. For example, we find that the instantaneous merger rate of m/M > 0.3 mass ratio events into typical L ∼> fL * galaxies follows the simple relation dN/dt ≅ 0.03(1+f)Gyr -1 (1+z) 2.1 . Despite the rapid increase in merger rate with redshift, only a small fraction of > 0.4L * high-redshift galaxies (∼ 3% at z = 2) should have experienced a major merger (m/M > 0.3) in the very recent past (t 0.3) in the last 700 Myr and conclude that mergers almost certainly play an important role in delivering baryons and influencing the kinematic properties of Lyman Break Galaxies (LBGs)

  17. General relativistic simulations of binary neutron star mergers

    Energy Technology Data Exchange (ETDEWEB)

    Giacomazzo, Bruno [Trento Univ. (Italy)

    2016-11-01

    Currently, we are running additional simulations to investigate additional models for the properties of dense matter. Furthermore, we are using remote visualization resources provided by LRZ to produce movies showing 3D visualizations of our simulations, which will be available soon on the web page of our group. One of the main challenges for our simulations is the fact that some important effects leading to magnetic field amplification happen on small length scales. This makes it very difficult to resolve them numerically. In order to further improve the accuracy, we proposed a follow- up study in which we will evolve one or more models with very high resolution and then use the results to calibrate a so-called sub-grid model, which is designed to capture the field amplification on scales not resolved with the lower, more affordable resolutions. Once calibrated, the sub-grid approach will allow to investigate a large number of models without the need for very high resolutions.

  18. General relativistic simulations of binary neutron star mergers

    International Nuclear Information System (INIS)

    Giacomazzo, Bruno

    2016-01-01

    Currently, we are running additional simulations to investigate additional models for the properties of dense matter. Furthermore, we are using remote visualization resources provided by LRZ to produce movies showing 3D visualizations of our simulations, which will be available soon on the web page of our group. One of the main challenges for our simulations is the fact that some important effects leading to magnetic field amplification happen on small length scales. This makes it very difficult to resolve them numerically. In order to further improve the accuracy, we proposed a follow- up study in which we will evolve one or more models with very high resolution and then use the results to calibrate a so-called sub-grid model, which is designed to capture the field amplification on scales not resolved with the lower, more affordable resolutions. Once calibrated, the sub-grid approach will allow to investigate a large number of models without the need for very high resolutions.

  19. 7 CFR 1717.152 - Required documentation for all mergers.

    Science.gov (United States)

    2010-01-01

    ... mergers. In order for RUS to advance funds, send bills, and otherwise conduct business with a successor..., borrowers must submit: (1) A transmittal letter on corporate letterhead signed by the manager of each active... evidence the merger pursuant to applicable law. Examples include plan of merger, articles of merger...

  20. 7 CFR 1782.15 - Mergers and consolidations.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 12 2010-01-01 2010-01-01 false Mergers and consolidations. 1782.15 Section 1782.15... AGRICULTURE (CONTINUED) SERVICING OF WATER AND WASTE PROGRAMS § 1782.15 Mergers and consolidations. Mergers... transaction under consideration and the unique facts involved in each transaction. Mergers occur when two or...

  1. An assessment of bank merger success in Germany

    NARCIS (Netherlands)

    Koetter, Michael

    German banks have experienced a merger wave since the early 1990s. However, the success or bank mergers remains a continuous matter or debate. This paper suggests a taxonomy to evaluate post-merger performance on the basis of cost and profit efficiency (CE and PE). I identify successful mergers as

  2. Music from the heavens - gravitational waves from supermassive black hole mergers in the EAGLE simulations

    Science.gov (United States)

    Salcido, Jaime; Bower, Richard G.; Theuns, Tom; McAlpine, Stuart; Schaller, Matthieu; Crain, Robert A.; Schaye, Joop; Regan, John

    2016-11-01

    We estimate the expected event rate of gravitational wave signals from mergers of supermassive black holes that could be resolved by a space-based interferometer, such as the Evolved Laser Interferometer Space Antenna (eLISA), utilizing the reference cosmological hydrodynamical simulation from the EAGLE suite. These simulations assume a Lambda cold dark matter cosmogony with state-of-the-art subgrid models for radiative cooling, star formation, stellar mass loss, and feedback from stars and accreting black holes. They have been shown to reproduce the observed galaxy population with unprecedented fidelity. We combine the merger rates of supermassive black holes in EAGLE with the latest phenomenological waveform models to calculate the gravitational waves signals from the intrinsic parameters of the merging black holes. The EAGLE models predict ˜2 detections per year by a gravitational wave detector such as eLISA. We find that these signals are largely dominated by mergers between seed mass black holes merging at redshifts between z ˜ 2 and z ˜ 1. In order to investigate the dependence on the assumed black hole seed mass, we introduce an additional model with a black hole seed mass an order of magnitude smaller than in our reference model. We also consider a variation of the reference model where a prescription for the expected delays in the black hole merger time-scale has been included after their host galaxies merge. We find that the merger rate is similar in all models, but that the initial black hole seed mass could be distinguished through their detected gravitational waveforms. Hence, the characteristic gravitational wave signals detected by eLISA will provide profound insight into the origin of supermassive black holes and the initial mass distribution of black hole seeds.

  3. Compact Binary Mergers and the Event Rate of Fast Radio Bursts

    Science.gov (United States)

    Cao, Xiao-Feng; Yu, Yun-Wei; Zhou, Xia

    2018-05-01

    Fast radio bursts (FRBs) are usually suggested to be associated with mergers of compact binaries consisting of white dwarfs (WDs), neutron stars (NSs), or black holes (BHs). We test these models by fitting the observational distributions in both redshift and isotropic energy of 22 Parkes FRBs, where, as usual, the rates of compact binary mergers (CBMs) are connected with cosmic star formation rates by a power-law distributed time delay. It is found that the observational distributions can well be produced by the CBM model with a characteristic delay time from several tens to several hundreds of megayears and an energy function index 1.2 ≲ γ ≲ 1.7, where a tentative fixed spectral index β = 0.8 is adopted for all FRBs. Correspondingly, the local event rate of FRBs is constrained to {(3{--}6)× {10}4{f}{{b}}-1({ \\mathcal T }/270{{s}})}-1{({ \\mathcal A }/2π )}-1 {Gpc}}-3 {yr}}-1 for an adopted minimum FRB energy of E min = 3 × 1039 erg, where f b is the beaming factor of the radiation, { \\mathcal T } is the duration of each pointing observation, and { \\mathcal A } is the sky area of the survey. This event rate, about an order of magnitude higher than the rates of NS–NS/NS–BH mergers, indicates that the most promising origin of FRBs in the CBM scenario could be mergers of WD–WD binaries. Here a massive WD could be produced since no FRB was found to be associated with an SN Ia. Alternatively, if all FRBs can repeat on a timescale much longer than the period of current observations, then they could also originate from a young active NS that forms from relatively rare NS–NS mergers and accretion-induced collapses of WD–WD binaries.

  4. Analysis of International Mergers and Acquisitions in the Pharmaceutical Industry

    Directory of Open Access Journals (Sweden)

    Božo Matić

    2011-07-01

    Full Text Available There are numerous researches which analyze mergers and acquisitions, but most of them do not focus on a certain industry, but their sample considers companies from different industries. This paper focuses on mergers and acquisitions in the pharmaceutical industry. It is assumed that pharmaceutical companies with no experience in mergers and acquisitions achieve better results in relatively small and domestic mergers and acquisitions while pharmaceutical companies with greater experience in mergers and acquisitions are successful even in bigger and international mergers and acquisitions. Bigger mergers and acquisitions and international mergers and acquisitions are more risky for the companies so lack of experience in mergers and acquisitions additionally increases risks during the process of mergers and acquisitions. On average, such increase of the risk results in lower returns for stock owners of pharmaceutical companies.

  5. Cost effects of hospital mergers in Portugal.

    Science.gov (United States)

    Azevedo, Helda; Mateus, Céu

    2014-12-01

    The Portuguese hospital sector has been restructured by wide-ranging hospital mergers, following a conviction among policy makers that bigger hospitals lead to lower average costs. Since the effects of mergers have not been systematically evaluated, the purpose of this article is to contribute to this area of knowledge by assessing potential economies of scale to explore and compare these results with realized cost savings after mergers. Considering the period 2003-2009, we estimate the translog cost function to examine economies of scale in the years preceding restructuring. Additionally, we use the difference-in-differences approach to evaluate hospital centres (HC) that occurred between 2004 and 2007, comparing the years after and before mergers. Our findings suggest that economies of scale are present in the pre-merger configuration with an optimum hospital size of around 230 beds. However, the mergers between two or more hospitals led to statistically significant post-merger cost increases, of about 8 %. This result indicates that some HC become too large to explore economies of scale and suggests the difficulty of achieving efficiencies through combining operations and service specialization.

  6. MAJOR MERGERS WITH SMALL GALAXIES: THE DISCOVERY OF A MAGELLANIC-TYPE GALAXY AT z = 0.12

    International Nuclear Information System (INIS)

    Koch, Andreas; Frank, Matthias J.; Pasquali, Anna; Rich, R. Michael; Rabitz, Andreas

    2015-01-01

    We report on the serendipitous discovery of a star-forming galaxy at redshift z = 0.116 with morphological features that indicate an ongoing merger. This object exhibits two clearly separated components with significantly different colors, plus a possible tidal stream. Follow-up spectroscopy of the bluer component revealed a low star-forming activity of 0.09 M ⊙ yr −1 and a high metallicity of 12 + log(O/H) = 8.6. Based on comparison with mass–star formation-rate and mass–metallicity relations, and on fitting of spectral energy distributions, we obtain a stellar mass of 3 × 10 9 M ⊙ , which renders this object comparable to the Large Magellanic Cloud. Thus our finding provides a further piece of evidence of a major merger already acting on small, dwarf-galaxy-like scales

  7. MAJOR MERGERS WITH SMALL GALAXIES: THE DISCOVERY OF A MAGELLANIC-TYPE GALAXY AT z = 0.12

    Energy Technology Data Exchange (ETDEWEB)

    Koch, Andreas; Frank, Matthias J. [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Pasquali, Anna [Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstrasse 12, D-69117 Heidelberg (Germany); Rich, R. Michael [University of California Los Angeles, Department of Physics and Astronomy, Los Angeles, CA (United States); Rabitz, Andreas, E-mail: akoch@lsw.uni-heidelberg.de [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)

    2015-12-20

    We report on the serendipitous discovery of a star-forming galaxy at redshift z = 0.116 with morphological features that indicate an ongoing merger. This object exhibits two clearly separated components with significantly different colors, plus a possible tidal stream. Follow-up spectroscopy of the bluer component revealed a low star-forming activity of 0.09 M{sub ⊙} yr{sup −1} and a high metallicity of 12 + log(O/H) = 8.6. Based on comparison with mass–star formation-rate and mass–metallicity relations, and on fitting of spectral energy distributions, we obtain a stellar mass of 3 × 10{sup 9} M{sub ⊙}, which renders this object comparable to the Large Magellanic Cloud. Thus our finding provides a further piece of evidence of a major merger already acting on small, dwarf-galaxy-like scales.

  8. ELECTROMAGNETIC COUNTERPARTS TO BLACK HOLE MERGERS DETECTED BY LIGO

    Energy Technology Data Exchange (ETDEWEB)

    Loeb, Abraham, E-mail: aloeb@cfa.harvard.edu [Department of Astronomy, Harvard University, 60 Garden St., Cambridge, MA 02138 (United States)

    2016-03-10

    Mergers of stellar-mass black holes (BHs), such as GW150914 observed by Laser Interferometer Gravitational Wave Observatory (LIGO), are not expected to have electromagnetic counterparts. However, the Fermi GBM detector identified a γ-ray transient 0.4 s after the gravitational wave (GW) signal GW150914 with consistent sky localization. I show that the two signals might be related if the BH binary detected by LIGO originated from two clumps in a dumbbell configuration that formed when the core of a rapidly rotating massive star collapsed. In that case, the BH binary merger was followed by a γ-ray burst (GRB) from a jet that originated in the accretion flow around the remnant BH. A future detection of a GRB afterglow could be used to determine the redshift and precise localization of the source. A population of standard GW sirens with GRB redshifts would provide a new approach for precise measurements of cosmological distances as a function of redshift.

  9. MERGERS IN DOUBLE-PEAKED [O III] ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Fu Hai; Djorgovski, S. G.; Myers, Adam D.; Yan Lin

    2011-01-01

    As a natural consequence of galaxy mergers, binary active galactic nuclei (AGNs) should be commonplace. Nevertheless, observational confirmations are rare, especially for binaries with separations less than 10 kpc. Such a system may show two sets of narrow emission lines in a single spectrum owing to the orbital motion of the binary. We have obtained high-resolution near-infrared images of 50 double-peaked [O III]λ5007 AGNs with the Keck II laser guide star adaptive optics system. The Sloan Digital Sky Survey sample is compiled from the literature and consists of 17 type-1 AGNs between 0.18 BH -σ * relation because of overestimated stellar velocity dispersions, illustrating the importance of removing mergers from the samples defining the M BH -σ * relations. Finally, we find that the emission-line properties are indistinguishable for spatially resolved and unresolved sources, emphasizing that scenarios involving a single AGN can produce the same double-peaked line profiles and they account for at least 70% of the double-peaked [O III] AGNs.

  10. Mergers and Product Quality: Evidence from the Airline Industry

    OpenAIRE

    Chen, Yongmin; Gayle, Philip

    2013-01-01

    Retrospective studies of horizontal mergers have focused on their price effects, leaving the important question of how mergers affect product quality largely unanswered. This paper empirically investigates this issue for two recent airline mergers: Delta/Northwest and Continental/United. Consistent with the theoretical premise that mergers improve coordination but diminish competitive pressure for quality provision, we find: (i) each merger is associated with a quality increase in markets whe...

  11. ROLE OF INTERNATIONAL MERGERS AND ACQUISITIONS IN CORPORATE INTEGRATION

    OpenAIRE

    Lucia P. BLĂJUȚ

    2015-01-01

    This paper highlights the role of international mergers and acquisitions in corporate integration. The factors that stimulate mergers and acquisitions activities bring real changes in the world economy. Mergers and acquisitions are a form of expansion: mergers can take place either as a statutory merger or consolidation and minority, majority or full acquisitions dominate the international market. It is very important to not confuse the meaning of the two terms. Multinational companies are fo...

  12. Getting cold feet?: Why health care mergers are abandoned.

    Science.gov (United States)

    Roos, Anne-Fleur; Postma, Jeroen

    2016-01-01

    Despite the frequent occurrence and sizeable consequences of merger abandonment in other sectors, there is no thorough understanding of merger abandonment in health care. The purpose of this study is to improve the understanding of determinants of health care merger abandonment. On the basis of the literature on merger abandonment, we formulated a framework on potential determinants of health care merger abandonment. We then constructed a survey that was sent to 70% of all executives of Dutch health care organizations (response rate = 35%, n = 291). We provide descriptive overviews of open, multiple-response, and multiple-choice questions on merger abandonment and use chi-square tests and Fisher's exact tests to test whether abandoned and completed merger processes differ. About 62% of the respondents were involved in at least one merger process during the period of 2005-2012. Thirty-eight percent of these respondents reported that their last merger case ended prematurely (n = 53). The most frequently mentioned determinants of merger abandonment are changing insights on the desirability and feasibility during merger processes, incompatibilities between executives, and insufficient support for the merger from internal stakeholders. We did not find significant relationships between merger abandonment and executives' previous merger experience, degree of organizational diversification, health care sector, size differences, or other organizational differences. Our findings partially confirm results from previous studies, especially with regard to the importance of changing insights and incompatibilities between the involved executives in merger abandonment. We also find that pressure from internal stakeholders, particularly nonexecutive directors, and distrust, fear, and animosity play an important role in merger abandonment. To minimize the organizational and societal costs of abandoned mergers, we advise executives who engage in mergers to construct backup plans with

  13. The Impact of Merger Status and Relative Representation on Identification with a Merger Group

    Directory of Open Access Journals (Sweden)

    Filip Boen

    2005-12-01

    Full Text Available This experiment tested to what extent identification with a new merger group is determined by the status of that merger group and by the relative representation of the pre-merger ingroup. One hundred university students were assigned to a team of 'inductive' thinkers, and were later merged with a team of 'deductive' thinkers to form a team of 'analyst' thinkers. The status of the merger group (low, high and the relative representation of the ingroup into the novel merger group (low, high were manipulated. Participants identified more with the merger group in the high than in the low status condition, and they identified more in the high than in the low representation condition. The predicted interaction between relative representation and merger status was not significant. However, relative representation did interact with participants' pre-merger identification: Pre- and post-merger identification were positively related when the ingroup was highly represented, but 'negatively' when the ingroup was lowly represented.

  14. MERGERS IN ΛCDM: UNCERTAINTIES IN THEORETICAL PREDICTIONS AND INTERPRETATIONS OF THE MERGER RATE

    International Nuclear Information System (INIS)

    Hopkins, Philip F.; Bundy, Kevin; Wetzel, Andrew; Ma, Chung-Pei; Croton, Darren; Khochfar, Sadegh; Hernquist, Lars; Genel, Shy; Van den Bosch, Frank; Somerville, Rachel S.; Keres, Dusan; Stewart, Kyle; Younger, Joshua D.

    2010-01-01

    Different theoretical methodologies lead to order-of-magnitude variations in predicted galaxy-galaxy merger rates. We examine how this arises and quantify the dominant uncertainties. Modeling of dark matter and galaxy inspiral/merger times contribute factor of ∼2 uncertainties. Different estimates of the halo-halo merger rate, the subhalo 'destruction' rate, and the halo merger rate with some dynamical friction time delay for galaxy-galaxy mergers, agree to within this factor of ∼2, provided proper care is taken to define mergers consistently. There are some caveats: if halo/subhalo masses are not appropriately defined the major-merger rate can be dramatically suppressed, and in models with 'orphan' galaxies and under-resolved subhalos the merger timescale can be severely over-estimated. The dominant differences in galaxy-galaxy merger rates between models owe to the treatment of the baryonic physics. Cosmological hydrodynamic simulations without strong feedback and some older semi-analytic models (SAMs), with known discrepancies in mass functions, can be biased by large factors (∼5) in predicted merger rates. However, provided that models yield a reasonable match to the total galaxy mass function, the differences in properties of central galaxies are sufficiently small to alone contribute small (factor of ∼1.5) additional systematics to merger rate predictions. But variations in the baryonic physics of satellite galaxies in models can also have a dramatic effect on merger rates. The well-known problem of satellite 'over-quenching' in most current SAMs-whereby SAM satellite populations are too efficiently stripped of their gas-could lead to order-of-magnitude under-estimates of merger rates for low-mass, gas-rich galaxies. Models in which the masses of satellites are fixed by observations (or SAMs adjusted to resolve this 'over-quenching') tend to predict higher merger rates, but with factor of ∼2 uncertainties stemming from the uncertainty in those

  15. Can this merger be saved?

    Science.gov (United States)

    Cliffe, S

    1999-01-01

    In this fictional case study, a merger that looked like a marriage made in heaven to those at corporate headquarters is feeling like an infernal union to those on the ground. The merger is between Synergon Capital, a U.S. financial-services behemoth, and Beauchamp, Becker & Company, a venerable British financial-services company with strong profits and an extraordinarily loyal client base of wealthy individuals. Beauchamp also boasts a strong group of senior managers led by Julian Mansfield, a highly cultured and beloved patriarch who personifies all that's good about the company. Synergon isn't accustomed to acquiring such companies. It usually encircles a poorly managed turnaround candidate and then, once the deal is done, drops a neutron bomb on it, leaving file cabinets and contracts but no people. Before acquiring Beauchamp, Synergon's macho men offered loud assurances that they would leave the tradition-bound company alone-provided, of course, that Beauchamp met the ambitious target numbers and showed sufficient enthusiasm for cross-selling Synergon's products to its wealthy clients. In charge of making the acquisition work is Nick Cunningham, one of Synergon's more thoughtful executives. Nick, who was against the deal from the start, is the face and voice of Synergon for Julian Mansfield. And Mansfield, in his restrained way, is angry at the constant flow of bureaucratic forms, at the rude demands for instant information, at the peremptory changes. He's even dropping broad hints at retirement. Nick has already been warned: if Mansfield goes, you go. Six commentators advise Nick on how to save his job by bringing peace and prosperity to the feuding couple.

  16. Dynamics of quadruple systems composed of two binaries: stars, white dwarfs, and implications for Ia supernovae

    Science.gov (United States)

    Fang, Xiao; Thompson, Todd A.; Hirata, Christopher M.

    2018-05-01

    We investigate the long-term secular dynamics and Lidov-Kozai (LK) eccentricity oscillations of quadruple systems composed of two binaries at quadrupole and octupole orders in the perturbing Hamiltonian. We show that the fraction of systems reaching high eccentricities is enhanced relative to triple systems, over a broader range of parameter space. We show that this fraction grows with time, unlike triple systems evolved at quadrupole order. This is fundamentally because with their additional degrees of freedom, quadruple systems do not have a maximal set of commuting constants of the motion, even in secular theory at quadrupole order. We discuss these results in the context of star-star and white dwarf-white dwarf (WD) binaries, with emphasis on WD-WD mergers and collisions relevant to the Type Ia supernova problem. For star-star systems, we find that more than 30 per cent of systems reach high eccentricity within a Hubble time, potentially forming triple systems via stellar mergers or close binaries. For WD-WD systems, taking into account general relativistic and tidal precession and dissipation, we show that the merger rate is enhanced in quadruple systems relative to triple systems by a factor of 3.5-10, and that the long-term evolution of quadruple systems leads to a delay-time distribution ˜1/t for mergers and collisions. In gravitational wave-driven mergers of compact objects, we classify the mergers by their evolutionary patterns in phase space and identify a regime in about 8 per cent of orbital shrinking mergers, where eccentricity oscillations occur on the general relativistic precession time-scale, rather than the much longer LK time-scale. Finally, we generalize previous treatments of oscillations in the inner binary eccentricity (evection) to eccentric mutual orbits. We assess the merger rate in quadruple and triple systems and the implications for their viability as progenitors of stellar mergers and Type Ia supernovae.

  17. IDENTIFYING ELUSIVE ELECTROMAGNETIC COUNTERPARTS TO GRAVITATIONAL WAVE MERGERS: AN END-TO-END SIMULATION

    International Nuclear Information System (INIS)

    Nissanke, Samaya; Georgieva, Alexandra; Kasliwal, Mansi

    2013-01-01

    Combined gravitational wave (GW) and electromagnetic (EM) observations of compact binary mergers should enable detailed studies of astrophysical processes in the strong-field gravity regime. This decade, ground-based GW interferometers promise to routinely detect compact binary mergers. Unfortunately, networks of GW interferometers have poor angular resolution on the sky and their EM signatures are predicted to be faint. Therefore, a challenging goal will be to unambiguously pinpoint the EM counterparts of GW mergers. We perform the first comprehensive end-to-end simulation that focuses on: (1) GW sky localization, distance measures, and volume errors with two compact binary populations and four different GW networks; (2) subsequent EM detectability by a slew of multiwavelength telescopes; and (3) final identification of the merger counterpart amidst a sea of possible astrophysical false positives. First, we find that double neutron star binary mergers can be detected out to a maximum distance of 400 Mpc (or 750 Mpc) by three (or five) detector GW networks, respectively. Neutron-star-black-hole binary mergers can be detected a factor of 1.5 further out; their median to maximum sky localizations are 50-170 deg 2 (or 6-65 deg 2 ) for a three (or five) detector GW network. Second, by optimizing depth, cadence, and sky area, we quantify relative fractions of optical counterparts that are detectable by a suite of different aperture-size telescopes across the globe. Third, we present five case studies to illustrate the diversity of scenarios in secure identification of the EM counterpart. We discuss the case of a typical binary, neither beamed nor nearby, and the challenges associated with identifying an EM counterpart at both low and high Galactic latitudes. For the first time, we demonstrate how construction of low-latency GW volumes in conjunction with local universe galaxy catalogs can help solve the problem of false positives. We conclude with strategies that would

  18. Getting to Yes on a Merger.

    Science.gov (United States)

    Burkhardt, John

    1994-01-01

    The merger of the University of Detroit and Mercy College (Michigan) is chronicled from early conversations through preparation and decision making. Salient issues that had to be addressed, especially persistent conflicts, and lessons learned from the experience are noted. (MSE)

  19. Mergers and acquisitions: a most strategic decision.

    Science.gov (United States)

    Laine, Mike; Tyler, David

    2007-11-01

    Five steps are basic to successfully concluding (or deciding not to conclude) a merger or acquisition: Identify targets. Begin with the end in mind. Choose a transaction team. Perform due diligence. Commit to the deal--or to no deal.

  20. DATA MINING THE GALAXY ZOO MERGERS

    Data.gov (United States)

    National Aeronautics and Space Administration — DATA MINING THE GALAXY ZOO MERGERS STEVEN BAEHR, ARUN VEDACHALAM, KIRK BORNE, AND DANIEL SPONSELLER Abstract. Collisions between pairs of galaxies usually end in the...

  1. Multiemployer Pension Plan Terminations, Mergers, and Insolvencies

    Data.gov (United States)

    Pension Benefit Guaranty Corporation — A listing of multiemployer pension plan terminations, mergers, and insolvencies reported to the PBGC for the current fiscal year. This data set will be updated...

  2. French bank mergers and acquisitions performance

    Directory of Open Access Journals (Sweden)

    Houda Ben Said

    2017-11-01

    Full Text Available In this paper, we empirically investigate the impact of mergers and acquisitions on French bank performance. Performance is measured by potential gains in efficiency and value creation. We first analyzed efficiency using the data envelopment analysis (DEA under input oriented with variable returns to scale to obtain the efficiency scores. Second, we analyzed the impact on French bank value creation following mergers-acquisitions operations of a set of control variables (model 1 and explicative variables measuring strategic similarities between bidders and targets (model 2. The sample studied is composed of French bank mergers-acquisitions happening between 1996 and 2006 and implying one of the 14 greatest French banking groups. Empirical result showed that mergers and acquisitions have been traduced by an improvement in the overall efficiency by 17.82% and a shareholder value reduction by 5.14%

  3. Models for mergers in higher education

    African Journals Online (AJOL)

    Investing in creativity: Many happy returns. Education Leadership, ... A possible model for higher education mergers, based on such extrapolation, is ..... working styles should be carefully managed from the very beginning of the process.

  4. Near-infrared to Mid-infrared Observations of Galaxy Mergers: NGC 2782 and NGC 7727

    Science.gov (United States)

    Onaka, Takashi; Nakamura, Tomohiko; Sakon, Itsuki; Wu, Ronin; Ohsawa, Ryou; Kaneda, Hidehiro; Lebouteiller, Vianney; Roellig, Thomas L.

    2018-01-01

    We present the results of near-infrared-to-mid-infrared (NIR-to-MIR) imaging and NIR spectroscopic observations of two galaxy mergers, NGC 2782 (Arp 215) and NGC 7727 (Arp 222), with the Infrared Camera on board AKARI. NGC 2782 shows extended MIR emission in the eastern side of the galaxy, which corresponds to the eastern tidal tail seen in the H I 21 cm map, while NGC 7727 shows extended MIR emission in the north of the galaxy, which is similar to the plumes seen in the residual image at the K-band after subtracting a galaxy model. Both extended structures are thought to have formed in association with their merger events. They show excess emission at 7–15 μm, which can be attributed to emission from polycyclic aromatic hydrocarbons (PAHs), while the observed spectral energy distributions (SEDs) decline longward of 24 μm, suggesting that very small grains (VSGs) are deficient. These characteristics of the observed MIR SED may be explained if PAHs are formed by fragmentation of VSGs during merger events. The star formation rate is estimated from the MIR PAH emission in the eastern tail region of NGC 2782 and it is in fair agreement with those estimated from Hα and [C II] 158 μm. MIR observations are efficient for the study of dust processing and structures formed during merger events.

  5. Astrophysical Implications of the Binary Black-hole Merger GW150914

    Science.gov (United States)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Behnke, B.; Bejger, M.; Belczynski, C.; Bell, A. S.; Bell, C. J.; Berger, B. K.; Bergman, J.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bodiya, T. P.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bojtos, P.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chakraborty, R.; Chalermsongsak, T.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M., Jr.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dattilo, V.; Dave, I.; Daveloza, H. P.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dereli, H.; Dergachev, V.; DeRosa, R.; DeRosa, R. T.; DeSalvo, R.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dojcinoski, G.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Franco, S.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fricke, T. T.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gatto, A.; Gaur, G.; Gehrels, N.; Gemme, G.; Gendre, B.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Hofman, D.; Hollitt, S. E.; Holt, K.; Holz, D. E.; Hopkins, P.; Hosken, D. J.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Idrisy, A.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Islas, G.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; K, Haris; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Karki, S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kawazoe, F.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalaidovski, A.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, C.; Kim, J.; Kim, K.; Kim, Nam-Gyu; Kim, Namjun; Kim, Y.-M.; King, E. J.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Kokeyama, K.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Krishnan, B.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Levine, B. M.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Logue, J.; Lombardi, A. L.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lück, H.; Lundgren, A. P.; Luo, J.; Lynch, R.; Ma, Y.; MacDonald, T.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magee, R. M.; Mageswaran, M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandel, I.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; Mazzolo, G.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mendoza-Gandara, D.; Mercer, R. A.; Merilh, E.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, C. L.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Necula, V.; Nedkova, K.; Nelemans, G.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Phelps, M.; Piccinni, O.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Premachandra, S. S.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, J. D.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sentenac, D.; Sequino, V.; Sergeev, A.; Serna, G.; Setyawati, Y.; Sevigny, A.; Shaddock, D. A.; Shah, S.; Shahriar, M. S.; Shaltev, M.; Shao, Z.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sigg, D.; Silva, A. D.; Simakov, D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stevenson, S. P.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Tomlinson, C.; Tonelli, M.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; van den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Welborn, T.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; White, D. J.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Worden, J.; Wright, J. L.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yap, M. J.; Yu, H.; Yvert, M.; Zadrożny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, F.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; and; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

    2016-02-01

    The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that inspiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively “heavy” BHs (≳ 25 {M}⊙ ) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 1/2 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (≳ 1 Gpc-3 yr-1) from both types of formation models. The low measured redshift (z≃ 0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.

  6. An Experimental Approach to Merger Evaluation

    OpenAIRE

    Christopher T. Conlon; Julie Holland Mortimer

    2013-01-01

    The 2010 Department of Justice and Federal Trade Commission Horizontal Merger Guidelines lay out a new standard for assessing proposed mergers in markets with differentiated products. This new standard is based on a measure of ``upward pricing pressure,'' (UPP) and the calculation of a ``gross upward pricing pressure index'' (GUPPI) in turn relies on a ``diversion ratio,'' which measures the fraction of consumers of one product that switch to another product when the price of the first produc...

  7. A weight limit emerges for neutron stars

    Science.gov (United States)

    Cho, Adrian

    2018-02-01

    Astrophysicists have long wondered how massive a neutron star—the corpse of certain exploding stars—could be without collapsing under its own gravity to form a black hole. Now, four teams have independently deduced a mass limit for neutron stars of about 2.2 times the mass of the sun. To do so, all four groups analyzed last year's blockbuster observations of the merger of two neutron stars, spied on 17 September 2017 by dozens of observatories. That approach may seem unpromising, as it might appear that the merging neutron stars would have immediately produced a black hole. However, the researchers argue that the merger first produced a spinning, overweight neutron star momentarily propped up by centrifugal force. They deduce that just before it collapsed, the short-lived neutron star had to be near the maximum mass for one spinning as a solid body. That inference allowed them to use a scaling relationship to estimate the maximum mass of a nonrotating, stable neutron star, starting from the total mass of the original pair and the amount of matter spewed into space.

  8. What Drive the Damage to Post-Merger Operating Performance?

    Directory of Open Access Journals (Sweden)

    Soegiharto Soegiharto

    2010-05-01

    Full Text Available This study examines whether bidders’ post-merger operat-ing performance are affected by their CEO behavior, premiumspaid to the target firms, the period of mergers, the method ofpayment, the industry of merged firms, capital liquidity, andtheir pre-merger operating performance. Testing the U.S. suc-cessful merger and acquisition data for the period of 1990s, thisstudy finds that in-wave mergers, intra-industry mergers, thepayment of lower premiums, and better pre-merger operatingperformance drive the bidders to produce better post-mergeroperating performance. Three measures of CEO behavior—themain predictor scrutinezed in this study—are proposed andexamined, and the results demonstrate that the effects of thesemeasures on post-merger operating performance are mixed,suggesting that each of the behavioral measures designed in thisstudy may capture CEO behavior in different ways. Keywords: capital liquidity; CEO overconfidence; merger waves, method of pay-ment operating performance

  9. On the origin of the hypervelocity runaway star HD 271791

    Science.gov (United States)

    Gvaramadze, V. V.

    2010-01-01

    We discuss the origin of the early-B-type runaway star HD 271791 and show that its extremely high velocity (≃530 - 920km s-1) cannot be explained within the framework of the binary-supernova ejection scenario. Instead, we suggest that HD 271791 attained its peculiar velocity in the course of a strong dynamical encounter between two hard, massive binaries or through an exchange encounter between a hard, massive binary and a very massive star, formed through runaway mergers of ordinary massive stars in the dense core of a young massive star cluster.

  10. When Mergers Fail: A Case Study on the Critical Role of External Stakeholders in Merger Initiatives

    Science.gov (United States)

    Stensaker, Bjørn; Persson, Mats; Pinheiro, Rómulo

    2016-01-01

    One can, in principle, identify numerous arguments for mergers in higher education (HE), including efficiency, diversity, quality, and regional needs. This diversity can be explained by the growing societal interest in the sector, not least concerning the contributions from HE to society at large. However, research on merger processes has tended…

  11. The challenge of merging : Merger patterns, premerger status, and merger support

    NARCIS (Netherlands)

    Giessner, [No Value; Täuber, Susanne; Viki, GT; Otten, S; Terry, DJ; Giessner, S.R

    Employees of merging organizations often show resistance to the merger. The employees' support depends on the companies' premerger status and on the merger pattern. Based on an inter-group perspective, three studies were conducted to investigate the influence of premerger status (high, low) and

  12. Change commitment in low-status merger partners: The role of information processing, relative ingroup prototypicality, and merger patterns.

    Science.gov (United States)

    Rosa, Miriam; Kavanagh, Eithne; Kounov, Pavel; Jarosz, Sywlia; Waldzus, Sven; Collins, Elizabeth C; Giessner, Steffen

    2017-09-01

    Merger announcements cause stress among employees, often leading to low change commitment, especially among employees from the lower-status merger partner. Such stress influences how deeply employees process merger-relevant information. Previous research examined how merger patterns that preserve versus change status differences impact merger support, but did not address how employees' information processing may influence this relationship. The current research addresses this gap through a scenario experiment, focusing on the low-status merger partner. The interplay between merger patterns and information processing was examined regarding employees' prototypicality claims in relation to merger support. Results suggest that an integration-equality merger pattern increases change commitment via prototypicality claims in the new organization, conditional to employees' systematic information processing. © 2017 The British Psychological Society.

  13. Quenching of Star Formation in Molecular Outflow Host NGC 1266

    NARCIS (Netherlands)

    Alatalo, K.; Nyland, K. E.; Graves, G.; Deustua, S.; Young, L. M.; Davis, T. A.; Crocker, A. F.; Bureau, M.; Bayet, E.; Blitz, L.; Bois, M.; Bournaud, F.; Cappellari, M.; Davies, R. L.; de Zeeuw, P. T.; Emsellem, E.; Khochfar, S.; Krajnovic, D.; Kuntschner, H.; McDermid, R. M.; Morganti, R.; Naab, T.; Oosterloo, T.; Sarzi, M.; Scott, N.; Serra, P.; Weijmans, A.; Wong, Tony; Ott, Jürgen

    We detail the rich molecular story of NGC 1266, its serendipitous discovery within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an AGN-driven molecular outflow, potentially quenching all of its star formation (SF) within the next 100 Myr. While major mergers appear to play a

  14. Risk Management in Mergers and Acquisitions

    Directory of Open Access Journals (Sweden)

    Dmitry O. Verdiev

    2015-01-01

    Full Text Available M&A statistics show that less than a third of newly merged companies has realized their planned synergistic effects and increased shareholder value. According to the author, such disgusting situation is due to improper planning and failure of corporate management to understand the importance of risk management in M&A. Lack of practice in identification, evaluation, mitigation and regular monitoring of risks leads to the situation when many companies merge despite the fact that the merger bears substantial risks. Corporate management fails to include risk mitigation expenses in merger costs. In many cases, risk mitigation expenses may be so substantive that the merger loses its attractiveness. Only few companies implement risk management methodology while planning M&A activity. This methodology may anticipate and minimize the consequences of various risk factors that negatively influence integration process. The article suggests an implementation of risk management best practice. This risk management best practice may act as an effective tool of successful realization of synergistic effects in M&A and may be helpful in increasing shareholder value in post-merger period. Risk management is conducted throughout the stages of merger and includes identification, analysis, assessment, management and monitoring of risks. Implementation of risk management at early stages of merger planning significantly decreases uncertainty in relation to achievement of financial and operational goals of newly merged company. The article provides with typical M&A risk matrix that may be adapted for specific M&A project. Risk matrix includes a register of risks sorted by stages of M&A deal, quality assessment of their probability, influence and impact on merger as well as risk mitigation methods.

  15. Descendants of the first stars: the distinct chemical signature of second generation stars

    Science.gov (United States)

    Hartwig, Tilman; Yoshida, Naoki; Magg, Mattis; Frebel, Anna; Glover, Simon C. O.; Gómez, Facundo A.; Griffen, Brendan; Ishigaki, Miho N.; Ji, Alexander P.; Klessen, Ralf S.; O'Shea, Brian W.; Tominaga, Nozomu

    2018-05-01

    Extremely metal-poor (EMP) stars in the Milky Way (MW) allow us to infer the properties of their progenitors by comparing their chemical composition to the metal yields of the first supernovae. This method is most powerful when applied to mono-enriched stars, i.e. stars that formed from gas that was enriched by only one previous supernova. We present a novel diagnostic to identify this subclass of EMP stars. We model the first generations of star formation semi-analytically, based on dark matter halo merger trees that yield MW-like halos at the present day. Radiative and chemical feedback are included self-consistently and we trace all elements up to zinc. Mono-enriched stars account for only ˜1% of second generation stars in our fiducial model and we provide an analytical formula for this probability. We also present a novel analytical diagnostic to identify mono-enriched stars, based on the metal yields of the first supernovae. This new diagnostic allows us to derive our main results independently from the specific assumptions made regarding Pop III star formation, and we apply it to a set of observed EMP stars to demonstrate its strengths and limitations. Our results may provide selection criteria for current and future surveys and therefore contribute to a deeper understanding of EMP stars and their progenitors.

  16. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  17. Dancing to CHANGA: a self-consistent prediction for close SMBH pair formation time-scales following galaxy mergers

    Science.gov (United States)

    Tremmel, M.; Governato, F.; Volonteri, M.; Quinn, T. R.; Pontzen, A.

    2018-04-01

    We present the first self-consistent prediction for the distribution of formation time-scales for close supermassive black hole (SMBH) pairs following galaxy mergers. Using ROMULUS25, the first large-scale cosmological simulation to accurately track the orbital evolution of SMBHs within their host galaxies down to sub-kpc scales, we predict an average formation rate density of close SMBH pairs of 0.013 cMpc-3 Gyr-1. We find that it is relatively rare for galaxy mergers to result in the formation of close SMBH pairs with sub-kpc separation and those that do form are often the result of Gyr of orbital evolution following the galaxy merger. The likelihood and time-scale to form a close SMBH pair depends strongly on the mass ratio of the merging galaxies, as well as the presence of dense stellar cores. Low stellar mass ratio mergers with galaxies that lack a dense stellar core are more likely to become tidally disrupted and deposit their SMBH at large radii without any stellar core to aid in their orbital decay, resulting in a population of long-lived `wandering' SMBHs. Conversely, SMBHs in galaxies that remain embedded within a stellar core form close pairs in much shorter time-scales on average. This time-scale is a crucial, though often ignored or very simplified, ingredient to models predicting SMBH mergers rates and the connection between SMBH and star formation activity.

  18. Lightweight Double Neutron Star Found

    Science.gov (United States)

    Kohler, Susanna

    2018-02-01

    More than forty years after the first discovery of a double neutron star, we still havent found many others but a new survey is working to change that.The Hunt for PairsThe observed shift in the Hulse-Taylor binarys orbital period over time as it loses energy to gravitational-wave emission. [Weisberg Taylor, 2004]In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylors measurements of this binarys decaying orbit over subsequent years led to a Nobel prize and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.Since the Hulse-Taylor binary, weve found a total of 16 additional double neutron-star systems which represents only a tiny fraction of the more than 2,600 pulsars currently known. Recently, however, a large number of pulsar surveys are turning their eyes toward the sky, with a focus on finding more double neutron stars and at least one of them has had success.The pulse profile for PSR J1411+2551 at 327 MHz. [Martinez et al. 2017]A Low-Mass DoubleConducted with the 1,000-foot Arecibo radio telescope in Puerto Rico, the Arecibo 327 MHz Drift Pulsar Survey has enabled the recent discovery of dozens of pulsars and transients. Among them, as reported by Jose Martinez (Max Planck Institute for Radio Astronomy) and coauthors in a recent publication, is PSR J1411+2551: a new double neutron star with one of the lowest masses ever measured

  19. Star formation suppression in compact group galaxies

    DEFF Research Database (Denmark)

    Alatalo, K.; Appleton, P. N.; Lisenfeld, U.

    2015-01-01

    , bars, rings, tidal tails, and possibly nuclear outflows, though the molecular gas morphologies are more consistent with spirals and earlytype galaxies than mergers and interacting systems. Our CO-imaged HCG galaxies, when plotted on the Kennicutt-Schmidt relation, shows star formation (SF) suppression...... color space. This supports the idea that at least some galaxies in HCGs are transitioning objects, where a disruption of the existing molecular gas in the system suppresses SF by inhibiting the molecular gas from collapsing and forming stars efficiently. These observations, combined with recent work...

  20. LIGO Discovers the Merger of Two Black Holes

    Science.gov (United States)

    Kohler, Susanna

    2016-02-01

    Big news: the Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected its first gravitational-wave signal! Not only is the detection of this signal a major technical accomplishment and an exciting confirmation of general relativity, but it also has huge implications for black-hole astrophysics.What did LIGO see?LIGO is designed to detect the ripples in space-time created by two massive objects orbiting each other. These waves can reach observable amplitudes when a binary system consisting of two especially massive objects i.e., black holes or neutron stars reach the end of their inspiral and merge.LIGO has been unsuccessfully searching for gravitational waves since its initial operations in 2002, but a recent upgrade in its design has significantly increased its sensitivity and observational range. The first official observing run of Advanced LIGO began 18 September 2015, but the instruments were up and running in engineering mode several weeks before that. And it was in this time frame before official observing even began! that LIGO spotted its first gravitational wave signal: GW150914.One of LIGOs two detection sites, located near Hanford in eastern Washington. [LIGO]The signal, detected on 14 September, 2015, provides astronomers with a remarkable amount of information about the merger that caused it. From the detection, the LIGO team has extracted the masses of the two black holes that merged, 36+5-4 and 29+4-4 solar masses, as well as the mass of the final black hole formed by the merger, ~62 solar masses. The team also determined that the merger happened roughly a billion light-years away (at a redshift of z~0.1), and the direction of the signal was localized to an area of ~600 square degrees (roughly 1% of the sky).Why is this detection a big deal?This is the firstdirect detection of gravitational waves, providing spectacular further confirmation of Einsteins theory of general relativity. But the implications of GW150914 go far beyond this

  1. A survey of dual active galactic nuclei in simulations of galaxy mergers: frequency and properties

    Science.gov (United States)

    Capelo, Pedro R.; Dotti, Massimo; Volonteri, Marta; Mayer, Lucio; Bellovary, Jillian M.; Shen, Sijing

    2017-08-01

    We investigate the simultaneous triggering of active galactic nuclei (AGN) in merging galaxies, using a large suite of high-resolution hydrodynamical simulations. We compute dual-AGN observability time-scales using bolometric, X-ray and Eddington-ratio thresholds, confirming that dual activity from supermassive black holes (BHs) is generally higher at late pericentric passages, before a merger remnant has formed, especially at high luminosities. For typical minor and major mergers, dual activity lasts ˜20-70 and ˜100-160 Myr, respectively. We also explore the effects of X-ray obscuration from gas, finding that the dual-AGN time decreases at most by a factor of ˜2, and of contamination from star formation. Using projected separations and velocity differences rather than three-dimensional quantities can decrease the dual-AGN time-scales by up to ˜4, and we apply filters that mimic current observational-resolution limitations. In agreement with observations, we find that for a sample of major and minor mergers hosting at least one AGN, the fraction harbouring dual AGN is ˜20-30 and ˜1-10 per cent, respectively. We quantify the effects of merger mass ratio (0.1 to 1), geometry (coplanar, prograde and retrograde, and inclined), disc gas fraction and BH properties, finding that the mass ratio is the most important factor, with the difference between minor and major mergers varying between factors of a few to orders of magnitude, depending on the luminosity and filter used. We also find that a shallow imaging survey will require very high angular resolution whereas a deep imaging survey will be less resolution-dependent.

  2. Can mergers make slowly rotating elliptical galaxies

    International Nuclear Information System (INIS)

    White, S.D.M.

    1979-01-01

    The results of numerical experiments are used to guide an analytic discussion of hyperbolic mergers among an uncorrelated galaxy population. The expected merger rate is derived as a function of progenitor mass and relative angular momentum, and is used to predict the distribution of the parameter V/sub c//sigma 0 for merger products where V/sub c/ is the maximum observed rotation velocity in a galaxy and sigma 0 is its central velocity dispersion. The median value of this parameter for mergers between comparable galaxies is estimated to be 0.65 and is higher than the observed value in any of the 14 galaxies for which data are available. It seems unlikely that most elliptical galaxies are the result of single or multiple mergers between initially unbound stellar systems; further observational and theoretical work is suggested which should lead to a conclusive test of this picture. The present arguments cannot, however, exclude formation from low angular momentum elliptical orbits

  3. [Effects of hospital mergers on health economy].

    Science.gov (United States)

    Ingebrigtsen, Tor

    2010-05-06

    Norwegian hospitals have been characterised by increasing activity, expansion of services and increasing costs for a long time. Differences in quality and accessibility have been documented between hospitals in various geographic locations. Transferral of hospital ownership to the state (from 2002) aimed at increasing capacities and improving quality of services, but also at restricting the increase of costs. These goals have only been partly met. The structure of hospital trusts and organisation of services are therefore continuously debated. This literature review aims at examining whether hospital mergers can reduce costs and at the same time increase the quality of services offered. Literature was identified through a Medline search using the terms "hospital", "merger" and "cost saving". The results are summarized and discussed. Seven original studies of totally 476 hospital mergers (in the USA, Great Britain and Norway) were identified in the period 1982 - 2000. The literature indicates that hospital mergers have a potential to reduce costs by about 10 % if the process achieves complete fusion of previously independent organisations, with a more optimal dimensioning of services and development of a common organizational culture. Collaboration between top management and the professional bureaucracy are prerequisites for success. Mergers are associated with a significant risk of unexpected problems and temporary reduced quality of the services.

  4. PERLINDUNGAN HUKUM TERHADAP KEPENTINGAN PARA PIHAK DI DALAM MERGER BANK

    Directory of Open Access Journals (Sweden)

    Dani Amran Hakim

    2016-04-01

    Full Text Available The legal protection of interests of the parties in the merger of banks, which is formulated into the problem as follows a Is the legal basis for bank mergers? b How is the legal protection of the parties in a bank merger? Merger is one of the company's development and growth. Merger is also one other alternative for capital investment through internal and organic growth. In banking mergers regulated in Law Number 10 of 1998. In the implementation of the merger must also consider the interests of the parties, namely, 1 the interests of the shareholders, 2 the interests of the depositors, 3 the interest of the bank employees, and 4 the interests of officials. Keywords: Protection Law, the Parties, Bank Merger 

  5. Merger 1980: The Organizational Integration of College Mental Health Services.

    Science.gov (United States)

    Foster, Thomas V., Jr.

    1982-01-01

    The merger of a traditional counseling center with a traditional comprehensive student health center at Indiana University, Bloomington is described. Important variables, costs and benefits, suggestions for similar mergers, and the outcome of the Indiana University program are discussed. (CJ)

  6. The problems of assessing the value of mergers and acquisitions

    Directory of Open Access Journals (Sweden)

    Borovikov A.D.

    2017-04-01

    Full Text Available the article discusses some questions concerning mergers and acquisitions of companies. The essential foundation of any mergers and acquisitions is always the competitive environment, more precisely, its constant changes.

  7. 29 CFR 4231.7 - De minimis mergers and transfers.

    Science.gov (United States)

    2010-07-01

    ... actuarial valuation. (b) De minimis merger defined. A merger is de minimis if the present value of accrued... market value of all the assets of the transferor plan; (2) The present value of the accrued benefits... value of the plan's assets is the highest. (1) A merger is not de minimis if the total present value of...

  8. Rethinking and re-imagining mergers in further and higher ...

    African Journals Online (AJOL)

    Higher and Further Education in South Africa has been characterized by major changes regarding the shape and size of the system. One of these changes has been the so-called mergers. This article addresses the scenario which contributed to the mergers. An overview of various frameworks or models for mergers is ...

  9. 29 CFR 4231.3 - Requirements for mergers and transfers.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 9 2010-07-01 2010-07-01 false Requirements for mergers and transfers. 4231.3 Section 4231..., REORGANIZATION, TERMINATION, AND OTHER RULES APPLICABLE TO MULTIEMPLOYER PLANS MERGERS AND TRANSFERS BETWEEN MULTIEMPLOYER PLANS § 4231.3 Requirements for mergers and transfers. (a) General requirements. A plan sponsor...

  10. 29 CFR 4011.6 - Mergers, consolidations, and spinoffs.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 9 2010-07-01 2010-07-01 false Mergers, consolidations, and spinoffs. 4011.6 Section 4011... REPORTING AND DISCLOSURE REQUIREMENTS DISCLOSURE TO PARTICIPANTS § 4011.6 Mergers, consolidations, and spinoffs. In the case of a plan involved in a merger, consolidation, or spinoff transaction that becomes...

  11. 7 CFR 1717.615 - Consolidations and mergers.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 11 2010-01-01 2010-01-01 false Consolidations and mergers. 1717.615 Section 1717.615... Controls § 1717.615 Consolidations and mergers. A distribution or power supply borrower may without the..., merger, conveyance or transfer shall be on such terms as shall fully preserve the lien and security of...

  12. 7 CFR 1735.62 - Approval of acquisitions and mergers.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 11 2010-01-01 2010-01-01 false Approval of acquisitions and mergers. 1735.62 Section 1735.62 Agriculture Regulations of the Department of Agriculture (Continued) RURAL UTILITIES SERVICE... Mortgage Controls on Acquisitions and Mergers § 1735.62 Approval of acquisitions and mergers. (a) If a...

  13. 7 CFR 1710.108 - Mergers and consolidations.

    Science.gov (United States)

    2010-01-01

    ... operating efficiency and financial soundness. (b) After a merger or consolidation, RUS will give priority... 7 Agriculture 11 2010-01-01 2010-01-01 false Mergers and consolidations. 1710.108 Section 1710.108... and Basic Policies § 1710.108 Mergers and consolidations. (a) RUS encourages its borrowers to consider...

  14. Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993

    Energy Technology Data Exchange (ETDEWEB)

    Palmese, A.; et al.

    2017-11-09

    We present a study of NGC 4993, the host galaxy of the GW170817 gravitational wave event, the GRB170817A short gamma-ray burst (sGRB) and the AT2017gfo kilonova. We use Dark Energy Camera imaging, AAT spectra and publicly available data, relating our findings to binary neutron star (BNS) formation scenarios and merger delay timescales. NGC4993 is a nearby (40 Mpc) early-type galaxy, with $i$-band S\\'ersic index $n=4.0$ and low asymmetry ($A=0.04\\pm 0.01$). These properties are unusual for sGRB hosts. However, NGC4993 presents shell-like structures and dust lanes indicative of a recent galaxy merger, with the optical transient located close to a shell. We constrain the star formation history (SFH) of the galaxy assuming that the galaxy merger produced a star formation burst, but find little to no on-going star formation in either spatially-resolved broadband SED or spectral fitting. We use the best-fit SFH to estimate the BNS merger rate in this type of galaxy, as $R_{NSM}^{gal}= 5.7^{+0.57}_{-3.3} \\times 10^{-6} {\\rm yr}^{-1}$. If star formation is the only considered BNS formation scenario, the expected number of BNS mergers from early-type galaxies detectable with LIGO during its first two observing seasons is $0.038^{+0.004}_{-0.022}$, as opposed to $\\sim 0.5$ from all galaxy types. Hypothesizing that the binary system formed due to dynamical interactions during the galaxy merger, the subsequent time elapsed can constrain the delay time of the BNS coalescence. By using velocity dispersion estimates and the position of the shells, we find that the galaxy merger occurred $t_{\\rm mer}\\lesssim 200~{\\rm Myr}$ prior to the BNS coalescence.

  15. Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993

    Science.gov (United States)

    Palmese, A.; Hartley, W.; Tarsitano, F.; Conselice, C.; Lahav, O.; Allam, S.; Annis, J.; Lin, H.; Soares-Santos, M.; Tucker, D.; Brout, D.; Banerji, M.; Bechtol, K.; Diehl, H. T.; Fruchter, A.; García-Bellido, J.; Herner, K.; Levan, A. J.; Li, T. S.; Lidman, C.; Misra, K.; Sako, M.; Scolnic, D.; Smith, M.; Abbott, T. M. C.; Abdalla, F. B.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Castander, F. J.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Davis, C.; DePoy, D. L.; Desai, S.; Dietrich, J. P.; Doel, P.; Drlica-Wagner, A.; Eifler, T. F.; Evrard, A. E.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Johnson, M. W. G.; Johnson, M. D.; Krause, E.; Kron, R.; Kuehn, K.; Kuhlmann, S.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; McMahon, R. G.; Menanteau, F.; Miller, C. J.; Miquel, R.; Neilsen, E.; Ogando, R. L. C.; Plazas, A. A.; Reil, K.; Romer, A. K.; Sanchez, E.; Schindler, R.; Smith, R. C.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Thomas, R. C.; Walker, A. R.; Weller, J.; Zhang, Y.; Zuntz, J.

    2017-11-01

    We present a study of NGC 4993, the host galaxy of the GW170817 gravitational-wave event, the GRB 170817A short gamma-ray burst (sGRB), and the AT 2017gfo kilonova. We use Dark Energy Camera imaging, AAT spectra, and publicly available data, relating our findings to binary neutron star (BNS) formation scenarios and merger delay timescales. NGC 4993 is a nearby early-type galaxy, with an I-band Sérsic index n = 4.0 and low asymmetry (A = 0.04 ± 0.01). These properties are unusual for sGRB hosts. However, NGC 4993 presents shell-like structures and dust lanes indicative of a recent galaxy merger, with the optical transient located close to a shell. We constrain the star formation history (SFH) of the galaxy assuming that the galaxy merger produced a star formation burst, but find little to no ongoing star formation in either spatially resolved broadband SED or spectral fitting. We use the best-fit SFH to estimate the BNS merger rate in this type of galaxy, as {R}{NSM}{gal}={5.7}-3.3+0.57× {10}-6{{yr}}-1. If star formation is the only considered BNS formation scenario, the expected number of BNS mergers from early-type galaxies detectable with LIGO during its first two observing seasons is {0.038}-0.022+0.004, as opposed to ˜0.5 from all galaxy types. Hypothesizing that the binary formed due to dynamical interactions during the galaxy merger, the subsequent time elapsed can constrain the delay time of the BNS coalescence. By using velocity dispersion estimates and the position of the shells, we find that the galaxy merger occurred t mer ≲ 200 Myr prior to the BNS coalescence.

  16. Railroad mergers and acquisitions take shape

    Energy Technology Data Exchange (ETDEWEB)

    Fiscor, S.

    1995-12-01

    This year has been one of the most exciting years in recent history concerning US railroads and coal transportation, as mergers and acquisitions narrow the field for Western coal carriers. The views on the mergers and how they will affect coal transportation are mixed. The coal industry`s growth in the West and its stability in the East is the basis for the most recent changes in the rail industry. Restructuring US coal markets to confirm to environmental policy has had a profound effect on much more than the coal industry itself. Deregulation of rail transport has also been an important factor. 1 fig., 3 tabs.

  17. UNVEILING THE σ-DISCREPANCY IN INFRARED-LUMINOUS MERGERS. I. DUST AND DYNAMICS

    International Nuclear Information System (INIS)

    Rothberg, Barry; Fischer, Jacqueline

    2010-01-01

    Mergers in the local universe present a unique opportunity for studying the transformations of galaxies in detail. Presented here are recent results, based on multi-wavelength, high-resolution imaging and medium resolution spectroscopy, which demonstrate how star formation and the presence of red supergiants and/or asymptotic giant branch stars have led to a serious underestimation of the dynamical masses of infrared-bright galaxies. The dominance of a nuclear disk of young stars in the near-infrared bands, where dust obscuration does not block their signatures, can severely bias the global properties measured in a galaxy, including mass. This explains why past studies of gas-rich luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies, which have measured dynamical masses using the 1.62 or 2.29 μm CO band heads, have found that these galaxies are forming m m* ellipticals. Moreover, merger remnants, including LIRGs, are placed on the I-band fundamental plane for the first time and appear to be virtually indistinguishable from elliptical galaxies.

  18. Direct formation of supermassive black holes via multi-scale gas inflows in galaxy mergers.

    Science.gov (United States)

    Mayer, L; Kazantzidis, S; Escala, A; Callegari, S

    2010-08-26

    Observations of distant quasars indicate that supermassive black holes of billions of solar masses already existed less than a billion years after the Big Bang. Models in which the 'seeds' of such black holes form by the collapse of primordial metal-free stars cannot explain the rapid appearance of these supermassive black holes because gas accretion is not sufficiently efficient. Alternatively, these black holes may form by direct collapse of gas within isolated protogalaxies, but current models require idealized conditions, such as metal-free gas, to prevent cooling and star formation from consuming the gas reservoir. Here we report simulations showing that mergers between massive protogalaxies naturally produce the conditions for direct collapse into a supermassive black hole with no need to suppress cooling and star formation. Merger-driven gas inflows give rise to an unstable, massive nuclear gas disk of a few billion solar masses, which funnels more than 10(8) solar masses of gas to a sub-parsec-scale gas cloud in only 100,000 years. The cloud undergoes gravitational collapse, which eventually leads to the formation of a massive black hole. The black hole can subsequently grow to a billion solar masses on timescales of about 10(8) years by accreting gas from the surrounding disk.

  19. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  20. Contribution of High-Mass Black Holes to Mergers of Compact Binaries

    International Nuclear Information System (INIS)

    Bethe, H.A.; Brown, G.E.

    1999-01-01

    We consider the merging of compact binaries consisting of a high-mass black hole and a neutron star. From stellar evolutionary calculations that include mass loss, we estimate that a zero-age main sequence (ZAMS) mass of approx-gt 80 M circle-dot is necessary before a high-mass black hole can result from a massive O star progenitor. We first consider how Cyg X-1, with its measured orbital radius of ∼17 R circle-dot , might evolve. Although this radius is substantially less than the initial distance of two O stars, it is still so large that the resulting compact objects will merge only if an eccentricity close to unity results from a high kick velocity of the neutron star in the final supernova explosion. We estimate the probability of the necessary eccentricity to be ∼1%; i.e., 99% of the time the explosion of a Cyg X-1 endash type object will end as a binary of compact stars, which will not merge in Hubble time (unless the orbit is tightened in common envelope evolution, which we discuss later). Although we predict ∼7 massive binaries of Cyg X-1 type, we argue that only Cyg X-1 is narrow enough to be observed, and that only Cyg X-1 has an appreciable chance of merging in Hubble time. This gives us a merging rate of ∼3x10 -8 yr -1 in the galaxy, the order of magnitude of the merging rate found by computer-driven population syntheses, if extrapolated to our mass limit of 80 M circle-dot ZAMS mass for high-mass black hole formation. Furthermore, in both our calculation and in those of population syntheses, almost all of the mergings involve an eccentricity close to unity in the final explosion of the O star. From this first part of our development we obtain only a negligible contribution to our final results for mergers, and it turns out to be irrelevant for our final results. In our main development, instead of relying on observed binaries, we consider the general evolution of binaries of massive stars. The critical stage is when the more massive star A has

  1. The determinants of merger waves: An international perspective

    Science.gov (United States)

    Gugler, Klaus; Mueller, Dennis C.; Weichselbaumer, Michael

    2012-01-01

    One of the most conspicuous features of mergers is that they come in waves that are correlated with increases in share prices and price/earnings ratios. We use a natural way to discriminate between pure stock market influences on firm decisions and other influences by examining merger patterns for both listed and unlisted firms. If “real” changes in the economy drive merger waves, as some neoclassical theories of mergers predict, both listed and unlisted firms should experience waves. We find significant differences between listed and unlisted firms as predicted by behavioral theories of merger waves. PMID:27346903

  2. Mergers and acquisitions in the oil and gas industries

    International Nuclear Information System (INIS)

    Corlay, C.; Huby, D.

    1999-01-01

    This paper focuses on mergers and acquisitions in the oil and gas industries, and lists the most important mergers in terms of transaction value for the period 1981-1997, and plots oil and gas mergers and acquisitions activity by sector and by major region. The mean operation indicator in 1998 in terms of reserves, production and refining capacity of the major companies are tabulated. The impact of the mergers on the oil and gas markets are examined, and issues concerning these mergers and acquisitions are explored. (UK)

  3. Mergers and acquisitions in the oil and gas industries

    Energy Technology Data Exchange (ETDEWEB)

    Corlay, C.; Huby, D. [Institut Francais du Petrole, Rueil-Malmaison (France)

    1999-07-01

    This paper focuses on mergers and acquisitions in the oil and gas industries, and lists the most important mergers in terms of transaction value for the period 1981-1997, and plots oil and gas mergers and acquisitions activity by sector and by major region. The mean operation indicator in 1998 in terms of reserves, production and refining capacity of the major companies are tabulated. The impact of the mergers on the oil and gas markets are examined, and issues concerning these mergers and acquisitions are explored. (UK)

  4. Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history

    Science.gov (United States)

    Poole, Gregory B.; Mutch, Simon J.; Croton, Darren J.; Wyithe, Stuart

    2017-12-01

    We introduce GBPTREES: an algorithm for constructing merger trees from cosmological simulations, designed to identify and correct for pathological cases introduced by errors or ambiguities in the halo finding process. GBPTREES is built upon a halo matching method utilizing pseudo-radial moments constructed from radially sorted particle ID lists (no other information is required) and a scheme for classifying merger tree pathologies from networks of matches made to-and-from haloes across snapshots ranging forward-and-backward in time. Focusing on SUBFIND catalogues for this work, a sweep of parameters influencing our merger tree construction yields the optimal snapshot cadence and scanning range required for converged results. Pathologies proliferate when snapshots are spaced by ≲0.128 dynamical times; conveniently similar to that needed for convergence of semi-analytical modelling, as established by Benson et al. Total merger counts are converged at the level of ∼5 per cent for friends-of-friends (FoF) haloes of size np ≳ 75 across a factor of 512 in mass resolution, but substructure rates converge more slowly with mass resolution, reaching convergence of ∼10 per cent for np ≳ 100 and particle mass mp ≲ 109 M⊙. We present analytic fits to FoF and substructure merger rates across nearly all observed galactic history (z ≤ 8.5). While we find good agreement with the results presented by Fakhouri et al. for FoF haloes, a slightly flatter dependence on merger ratio and increased major merger rates are found, reducing previously reported discrepancies with extended Press-Schechter estimates. When appropriately defined, substructure merger rates show a similar mass ratio dependence as FoF rates, but with stronger mass and redshift dependencies for their normalization.

  5. THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS

    International Nuclear Information System (INIS)

    Rupke, David S. N.; Veilleux, Sylvain

    2013-01-01

    Massive, galaxy-scale outflows are known to be ubiquitous in major mergers of disk galaxies in the local universe. In this paper, we explore the multiphase structure and power sources of galactic winds in six ultraluminous infrared galaxies (ULIRGs) at z –1 , and the highest velocities (2000-3000 km s –1 ) are seen only in ionized gas. The outflow energy and momentum in the QSOs are difficult to produce from a starburst alone, but are consistent with the QSO contributing significantly to the driving of the flow. Finally, when all gas phases are accounted for, the outflows are massive enough to provide negative feedback to star formation.

  6. On the origin of the hypervelocity runaway star HD271791

    OpenAIRE

    Gvaramadze, V. V.

    2009-01-01

    We discuss the origin of the runaway early B-type star HD271791 and show that its extremely high velocity (\\simeq 530-920 km/s) cannot be explained within the framework of the binary-supernova ejection scenario. Instead, we suggest that HD271791 attained its peculiar velocity in the course of a strong dynamical encounter between two hard massive binaries or via an exchange encounter between a hard massive binary and a very massive star, formed through runaway mergers of ordinary massive stars...

  7. DRY MERGER RATE AND POST-MERGER FRACTION IN THE COMA CLUSTER CORE

    Energy Technology Data Exchange (ETDEWEB)

    Cordero, Juan P.; Campusano, Luis E.; Haines, Christopher P. [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); De Propris, Roberto [Finnish Centre for Astronomy with ESO, University of Turku, Vaisalantie 20, Piikkio, FI-21500 (Finland); Weinzirl, Tim [School of Physics and Astronomy, The University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Jogee, Shardha, E-mail: jcordero@das.uchile.cl [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712-1205 (United States)

    2016-01-20

    We evaluate the dry merger activity in the Coma cluster, using a spectroscopically complete sample of 70 red-sequence (RS) galaxies, most of which (∼75%) are located within 0.2R{sub 200} (∼0.5 Mpc) from the cluster center, with data from the Coma Treasury Survey obtained with the Hubble Space Telescope. The fraction of close galaxy pairs in the sample is the proxy employed for the estimation of the merger activity. We identify 5 pairs and 1 triplet, enclosing a total of 13 galaxies, based on limits on projected separation and line-of-sight velocity difference. Of these systems, none show signs of ongoing interaction, and therefore we do not find any true mergers in our sample. This negative result sets a 1σ upper limit of 1.5% per Gyr for the major dry merger rate, consistent with the low rates expected in present-day clusters. Detailed examination of the images of all the RS galaxies in the sample reveals only one with low surface brightness features identifiable as the remnant of a past merger or interaction, implying a post-merger fraction below 2%.

  8. DRY MERGER RATE AND POST-MERGER FRACTION IN THE COMA CLUSTER CORE

    International Nuclear Information System (INIS)

    Cordero, Juan P.; Campusano, Luis E.; Haines, Christopher P.; De Propris, Roberto; Weinzirl, Tim; Jogee, Shardha

    2016-01-01

    We evaluate the dry merger activity in the Coma cluster, using a spectroscopically complete sample of 70 red-sequence (RS) galaxies, most of which (∼75%) are located within 0.2R 200 (∼0.5 Mpc) from the cluster center, with data from the Coma Treasury Survey obtained with the Hubble Space Telescope. The fraction of close galaxy pairs in the sample is the proxy employed for the estimation of the merger activity. We identify 5 pairs and 1 triplet, enclosing a total of 13 galaxies, based on limits on projected separation and line-of-sight velocity difference. Of these systems, none show signs of ongoing interaction, and therefore we do not find any true mergers in our sample. This negative result sets a 1σ upper limit of 1.5% per Gyr for the major dry merger rate, consistent with the low rates expected in present-day clusters. Detailed examination of the images of all the RS galaxies in the sample reveals only one with low surface brightness features identifiable as the remnant of a past merger or interaction, implying a post-merger fraction below 2%

  9. Corporate Employee-Engagement and Merger Outcomes

    NARCIS (Netherlands)

    Liang, H.; Renneboog, Luc

    2017-01-01

    Extending the theories of employee incentives and inalienability of human capital, we investigate the link between a firm’s engagement in employee issues and the returns to shareholders around mergers and acquisitions (M&As) and analyze an international sample of 4,565 M&A deals from 48 countries.

  10. Mergers and innovation in the pharmaceutical industry.

    Science.gov (United States)

    Comanor, William S; Scherer, F M

    2013-01-01

    Conflicting trends confound the pharmaceutical industry. The productivity of pharmaceutical innovation has declined in recent years. At the same time, the cohort of large companies who are the leading engines of pharmaceutical R&D has become increasingly concentrated. The concurrent presence of these trends is not sufficient to determine causation. In response to lagging innovation prospects, some companies have sought refuge in mergers and acquisitions to disguise their dwindling prospects or gain R&D synergies. On the other hand, the increased concentration brought on by recent mergers may have contributed to the declining rate of innovation. In this paper, we consider the second of these causal relationships: the likely impact of the recent merger wave among the largest pharmaceutical companies on the rate of innovation. In other words, have recent mergers, which may have been taken in response to lagging innovation, represented a self-defeating strategy that only made industry outcomes worse? Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Bargaining in Mergers and Termination Fees

    NARCIS (Netherlands)

    Weitzel, U.; Rosenkranz, S.

    We model takeovers as a bargaining process and explain termination fees for, both, the target and the acquirer, subject to parties’ bargaining power and outside options. In equilibrium, termination fees are offered by firms with outside options in exchange for a greater share of merger synergies.

  12. Mergers and acquisitions involving equine veterinary practices.

    Science.gov (United States)

    Jackman, Brad R; McCafferty, Owen E

    2009-12-01

    This article discusses mergers and acquisitions involving equine veterinary practices. Combining practices can be professionally and economically advantageous but requires a great deal of thought, planning, and implementation. If due diligence is performed and true business teamwork is undertaken, the benefits can be enormous and rewarding.

  13. Cross-border Mergers and Acquisitions

    DEFF Research Database (Denmark)

    Wang, Daojuan

    This paper focuses on three topics in cross-border mergers and acquisitions (CBM&As) field: motivations for CBM&As, valuation techniques and CBM&A performance (assessment and the determinants). By taking an overview of what have been found so far in academic field and investigating...

  14. Mergers and acquisitions: valuation and risk assessment

    International Nuclear Information System (INIS)

    Calvin, B.N.

    1996-01-01

    An independent review of all facets of risk management, as it pertains to mergers and acquisitions within the petroleum industry, with no transactional motivation, was provided by a representative of a firm specializing in all phases of risk assessment. The following topics received attention: (1) the forward curve versus industry expectations, (2) investor expectations, (3) financial versus physical transactions, and (4) synthetic debt

  15. Technology-based Mergers and Acquisitions

    DEFF Research Database (Denmark)

    Wang, Daojuan; Moini, Hamid

    2014-01-01

    The purpose of this chapter is to provide an updated review of what is known about the performance of technology-based mergers and acquisitions (TBM&As) and their determinants. This review brings together papers published from 1990 to 2012 in top-rated academic journals within nearly all fields...

  16. Fueling QSOs: the relevance of mergers

    Czech Academy of Sciences Publication Activity Database

    Bennert, N.; Canalizo, G.; Jungwiert, Bruno; Stockton, A.; Schweizer, F.; Peng, Ch.; Lacy, M.

    2008-01-01

    Roč. 79, č. 4 (2008), s. 1247-1250 ISSN 0037-8720 R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxy mergers * quasars * photometry Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  17. Mergers and alliances the wider view

    CERN Document Server

    Woodsworth, Anne

    2013-01-01

    Volume 36 of Advances in Librarianship seeks to provide a broad review of the factors that lead to mergers and other alliances, the methods used to ensure effective and successful collaborations, and descriptions of the factors which contributed to less successful efforts at consolidation.

  18. Using transfer learning to detect galaxy mergers

    Science.gov (United States)

    Ackermann, Sandro; Schawinksi, Kevin; Zhang, Ce; Weigel, Anna K.; Turp, M. Dennis

    2018-05-01

    We investigate the use of deep convolutional neural networks (deep CNNs) for automatic visual detection of galaxy mergers. Moreover, we investigate the use of transfer learning in conjunction with CNNs, by retraining networks first trained on pictures of everyday objects. We test the hypothesis that transfer learning is useful for improving classification performance for small training sets. This would make transfer learning useful for finding rare objects in astronomical imaging datasets. We find that these deep learning methods perform significantly better than current state-of-the-art merger detection methods based on nonparametric systems like CAS and GM20. Our method is end-to-end and robust to image noise and distortions; it can be applied directly without image preprocessing. We also find that transfer learning can act as a regulariser in some cases, leading to better overall classification accuracy (p = 0.02). Transfer learning on our full training set leads to a lowered error rate from 0.0381 down to 0.0321, a relative improvement of 15%. Finally, we perform a basic sanity-check by creating a merger sample with our method, and comparing with an already existing, manually created merger catalogue in terms of colour-mass distribution and stellar mass function.

  19. Merger incentives and the failing firm defense

    NARCIS (Netherlands)

    Bouckaert, J.M.C.; Kort, P.M.

    2014-01-01

    The merger incentives between profitable firms differ fundamentally from the incentives of a profitable firm to merge with a failing firm. We investigate these incentives under different modes of price competition and Cournot behavior. Our main finding is that firms strictly prefer exit of the

  20. Efficiency Effects of Bank Mergers and Acquisitions

    NARCIS (Netherlands)

    H.P. Huizinga; J.H.M. Nelissen (Jan); R. Vander Vennet

    2001-01-01

    textabstractNext to technological progress and deregulation, the introduction of the euro is widely considered to be an important catalyst for bank consolidation in Europe. In order to assess the public policy issues surrounding bank mergers, this paper analyzes the efficiency effects of 52

  1. Merger and Acquisition in the Banking Sector

    Directory of Open Access Journals (Sweden)

    Anna Szewczyk

    2008-12-01

    Full Text Available The article presents situation on mergers and acquisitions (MA in banking sector during last twenty years. The main motives are selected and analyzed. All is explained on the base on research reports of the Deutsche Bundesbank and the European Central Bank.

  2. Resilience and Coping After Hospital Mergers.

    Science.gov (United States)

    Russo, Cynthia; Calo, Oriana; Harrison, Georgia; Mahoney, Kathleen; Zavotsky, Kathleen Evanovich

    The aim of this study was to explore the relationship between resilience and coping in frontline nurses working in a healthcare system that has recently undergone a merger. Hospital mergers are common in the current healthcare environment. Mergers can provide hospital nurses the opportunity to use and develop positive coping strategies to help remain resilient during times of change. An anonymous-survey, quantitative, exploratory, descriptive study design was used. Data were obtained from an electronic survey that was made available to all nurses working in a 3-hospital system located in the northeast. Overall, the results showed that, when nurses reported using positive coping strategies, they report higher levels of resilience. The levels of resilience also varied from campus to campus. The campus that has been through 2 recent mergers reported the highest levels of resilience. This study suggests that, during times of change in the workplace, if nurses are encouraged to use positive coping strategies, they may have higher levels of resilience. This changing environment provides the clinical nurse specialists/clinical nurse educators the opportunity to foster and support frontline nurses in the use of healthy coping strategies and to help improve and maintain a high level of resilience, which is critical in today's healthcare environment.

  3. A CEO roundtable on making mergers succeed.

    Science.gov (United States)

    Mandl, A; Bohnett, D; Liddy, E; Komansky, D; Kozlowski, D; Leschly, J; Gupta, R; McDonald, M; Avery, B; Moore, N; Krekel, T

    2000-01-01

    The announcement in January of the merger between America Online and Time Warner marked the convergence of the two most important business trends of the last five years--the rise of the Internet and the resurgence of mergers and acquisitions. M&A activity is at a fever pitch, spurred in large part by the breathtaking influx of capital into the Internet space. And all signs indicate the trend will only accelerate. Against this background, an impressive group of experienced deal makers came together to share their experiences of what makes mergers work. They were assembled in Scottsdale, Arizona, under the auspices of the M&A Group, a professional society formed in 1999 for CEOs interested in M&A as a business strategy. Participants included top executives from Internet start-ups like Teligent; venture capital firms like Baroda Ventures; financial institutions like Merrill Lynch and PricewaterhouseCoopers; and major corporations like Allstate, Tyco International, SmithKline Beecham, Rohm and Haas, VF, Crown Cork & Seal, and Hughes Space and Communications. The spirited and surprisingly frank discussion cut a wide swath, considering issues such as whether most mergers fail to pan out as well as expected, how to increase the odds of success, the nuts and bolts of the integration process, the trade-offs between acquiring a company and growing from within, the importance of cultural issues, and why anyone would want to be on the board of a merged company.

  4. The AGN Luminosity Fraction in Galaxy Mergers

    Science.gov (United States)

    Dietrich, Jeremy; Weiner, Aaron; Ashby, Matthew; Martinez-Galarza, Juan Rafael; Smith, Howard Alan

    2017-01-01

    Galaxy mergers are key events in galaxy evolution, generally triggering massive starbursts and AGNs. However, in these chaotic systems, it is not yet known what fraction each of these two mechanisms contributes to the total luminosity. Here we measure and model spectral energy distributions (SEDs) using the Code for Investigating Galaxy Emission (CIGALE) in up to 33 broad bands from the UV to the far-IR for 23 IR-luminous galaxies to estimate the fraction of the bolometric IR luminosity that can be attributed to the AGN. The galaxies are split nearly evenly into two subsamples: late-stage mergers, found in the IRAS Revised Bright Galaxy Sample or Faint Source Catalog, and early-stage mergers found in the Spitzer Interacting Galaxy Sample. We find that the AGN contribution to the total IR luminosity varies greatly from system to system, from 0% up to ~90%, but is substantially greater in the later-stage and brighter mergers. This is consistent with what is known about galaxy evolution and the triggering of AGNs.The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.

  5. Synergy disclosures in mergers and acquisitions

    NARCIS (Netherlands)

    M.D.R.P. Dutordoir (Marie); P.G.J. Roosenboom (Peter); M. Teixeira de Vasconcelos (Manuel)

    2013-01-01

    textabstractWe examine bidding firms’ motives for disclosing a synergy forecast when announcing a merger or acquisition. Our sample consists of 1,990 M&A deals, of which 345 announce synergy estimates. Our results suggest that synergy disclosures serve to obtain a more favorable market reception for

  6. Shareholders’ expectations, aspiration levels, and mergers

    NARCIS (Netherlands)

    Diecidue, E.; van de Ven, J.; Weitzel, U.

    This paper offers a new explanation of value-reducing mergers and stock market driven takeovers by introducing recent research on aspiration levels and individual decision making under risk. If market valuation constitutes an aspiration level for managers, we show that managers may be tempted to

  7. Ultraluminous Infrared Mergers: Elliptical Galaxies in Formation?

    Science.gov (United States)

    Genzel, R.; Tacconi, L. J.; Rigopoulou, D.; Lutz, D.; Tecza, M.

    2001-12-01

    We report high-quality near-IR spectroscopy of 12 ultraluminous infrared galaxy mergers (ULIRGs). Our new VLT and Keck data provide ~0.5" resolution, stellar and gas kinematics of these galaxies, most of which are compact systems in the last merger stages. We confirm that ULIRG mergers are ``ellipticals in formation.'' Random motions dominate their stellar dynamics, but significant rotation is common. Gasdynamics and stellar dynamics are decoupled in most systems. ULIRGs fall on or near the fundamental plane of hot stellar systems, and especially on its less evolution-sensitive, reff-σ projection. The ULIRG velocity dispersion distribution, their location in the fundamental plane, and their distribution of vrotsini/σ closely resemble those of intermediate-mass (~L*), elliptical galaxies with moderate rotation. As a group ULIRGs do not resemble giant ellipticals with large cores and little rotation. Our results are in good agreement with other recent studies indicating that disky ellipticals with compact cores or cusps can form through dissipative mergers of gas-rich disk galaxies while giant ellipticals with large cores have a different formation history. Based on observations at the European Southern Observatory, Chile (ESO 65.N-0266, 65.N-0289), and on observations at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, The University of California, and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the general financial support by the W. M. Keck Foundation.

  8. Dynamical study of merger remnants

    International Nuclear Information System (INIS)

    Lake, G.; Dressler, A.; ATandT Bell Labs., Murray Hill, NJ; Mount Wilson and Las Campanas Observatories, Pasadena, CA; Carnegie Institution of Washington, Washington, DC)

    1986-01-01

    The velocity dispersion of objects from the Arp and the Arp-Madore atlases that have characteristics of recently merged galaxies is measured. These data are used to test the hypothesis that the remnants become normal elliptical galaxies after the fireworks of recent star formation subside. Accurate velocity dispersions of objects dominated by Balmer lines in the blue were measured using the uncontaminated Ca triplet feature in the extreme red (8400-8700 A). No deviation from the velocity dispersion expected for elliptical galaxies of comparable luminosity, is found, e.g., these systems follow the usual L-sigma relation with no zero-point shift. For a few galaxies without Balmer contamination, stellar rotation velocities are determined. One slow, one moderate, and one fast rotator are found. 54 references

  9. A binary neutron star GRB model

    International Nuclear Information System (INIS)

    Wilson, J.R.; Salmonson, J.D.; Wilson, J.R.; Mathews, G.J.

    1998-01-01

    In this paper we present the preliminary results of a model for the production of gamma-ray bursts (GRBs) through the compressional heating of binary neutron stars near their last stable orbit prior to merger. Recent numerical studies of the general relativistic (GR) hydrodynamics in three spatial dimensions of close neutron star binaries (NSBs) have uncovered evidence for the compression and heating of the individual neutron stars (NSs) prior to merger 12. This effect will have significant effect on the production of gravitational waves, neutrinos and, ultimately, energetic photons. The study of the production of these photons in close NSBs and, in particular, its correspondence to observed GRBs is the subject of this paper. The gamma-rays arise as follows. Compressional heating causes the neutron stars to emit neutrino pairs which, in turn, annihilate to produce a hot electron-positron pair plasma. This pair-photon plasma expands rapidly until it becomes optically thin, at which point the photons are released. We show that this process can indeed satisfy three basic requirements of a model for cosmological gamma-ray bursts: (1) sufficient gamma-ray energy release (>10 51 ergs) to produce observed fluxes, (2) a time-scale of the primary burst duration consistent with that of a 'classical' GRB (∼10 seconds), and (3) the peak of the photon number spectrum matches that of 'classical' GRB (∼300 keV). copyright 1998 American Institute of Physics

  10. SPIN-PRECESSION: BREAKING THE BLACK HOLE-NEUTRON STAR DEGENERACY

    Energy Technology Data Exchange (ETDEWEB)

    Chatziioannou, Katerina; Cornish, Neil; Klein, Antoine; Yunes, Nicolás [Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

    2015-01-01

    Mergers of compact stellar remnants are prime targets for the LIGO/Virgo gravitational wave detectors. The gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.

  11. The Final Merger of Massive Black Holes: Recoils, Gravitational Waves, and Electromagnetic Signatures

    Science.gov (United States)

    Centrella, Joan M.

    2010-01-01

    The final merger of two massive black holes produces a powerful burst of gravitational radiation, emitting more energy than all the stars in the observable universe combined. The resulting gravitational waveforms will be easily detectable by the space-based LISA out to redshifts z greater than 10, revealing the masses and spins of the black holes to high precision. If the merging black holes have unequal masses, or asymmetric spins, the final black hole that forms can recoil with a velocity exceeding 1000 km/s. And, when the black holes merge in the presence of gas and magnetic fields, various types of electromagnetic signals may also be produced. For more than 30 years, scientists have tried to compute black hole mergers using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. Within the past few years, however, this situation has changed dramatically, with a series of remarkable breakthroughs. This talk will focus on new results that are revealing the dynamics and waveforms of binary black hole mergers, recoil velocities, and the possibility of accompanying electromagnetic outbursts.

  12. THE ROLE OF DRY MERGERS FOR THE FORMATION AND EVOLUTION OF BRIGHTEST CLUSTER GALAXIES

    International Nuclear Information System (INIS)

    Ruszkowski, M.; Springel, V.

    2009-01-01

    Using a resimulation technique, we perform high-resolution cosmological simulations of dry mergers in a massive (10 15 M sun ) galaxy cluster identified in the Millennium Run. Our initial conditions include well resolved compound galaxy models consisting of dark matter halos and stellar bulges that are used to replace the most massive cluster progenitor halos at redshift z = 3, allowing us to follow the subsequent dry merger processes that build up the cluster galaxies in a self-consistent cosmological setting. By construction, our galaxy models obey the stellar mass-size relation initially. Also, we study both galaxy models with adiabatically contracted and uncompressed halos. We demonstrate that the brightest cluster galaxy (BCG) evolves away from the Kormendy relation as defined by the smaller mass galaxies (i.e., the relation bends). This is accompanied by a significantly faster dark matter mass growth within the half-light radius of the BCG compared to the increase in the stellar mass inside the same radius. As a result of the comparatively large number of mergers the BCG experiences, its total mass-to-light ratio becomes significantly higher than in typical elliptical galaxies. We also show that the mixing processes between dark matter and stars lead to a small but numerically robust tilt in the fundamental plane and that the BCG lies on the tilted plane. Our model is consistent with the observed steepening of the logarithmic mass-to-light gradient as a function of the stellar mass. As we have not included effects from gas dynamics or star formation, these trends are exclusively due to N-body and stellar dynamical effects. Surprisingly, we find only tentative weak distortion in the Faber-Jackson relation that depends on the aperture size, unlike expected based on studies of isolated merger simulations. This may be due to differences in the distribution of galaxy orbits, which is given in our approach directly by the cosmological context while it has to be

  13. A 2-3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts

    Science.gov (United States)

    Hammer, F.; Yang, Y. B.; Wang, J. L.; Ibata, R.; Flores, H.; Puech, M.

    2018-04-01

    Recent observations of our neighbouring galaxy M31 have revealed that its disc was shaped by widespread events. The evidence for this includes the high dispersion (V/σ ≤ 3) of stars older than 2 Gyr, and a global star formation episode, 2-4 Gyr ago. Using the modern hydrodynamical code, GIZMO, we have performed 300 high-resolution simulations to explore the extent to which these observed properties can be explained by a single merger. We find that the observed M31 disc resembles models having experienced a 4:1 merger, in which the nuclei coalesced 1.8-3 Gyr ago, and where the first passage took place 7-10 Gyr ago at a large pericentre distance (32 kpc). We also show that within a family of orbital parameters, the Giant Stream (GS) can be formed with various merger mass ratios, from 2:1 to 300:1. A recent major merger may be the only way to create the very unusual age-dispersion relation in the disc. It reproduces and explains the long-lived 10 kpc ring, the widespread and recent star formation event, the absence of a remnant of the GS progenitor, the apparent complexity of the 3D spatial distribution of the GS, the NE and G Clumps and their formation process, and the observed slope of the halo profile. These modelling successes lead us to propose that the bulk of the substructure in the M31 halo, as well as the complexity of the inner galaxy, may be attributable to a single major interaction with a galaxy that has now fully coalesced with Andromeda.

  14. STAR FORMATION PROPERTIES IN BARRED GALAXIES (SFB). I. ULTRAVIOLET TO INFRARED IMAGING AND SPECTROSCOPIC STUDIES OF NGC 7479

    International Nuclear Information System (INIS)

    Zhou Zhimin; Meng Xianmin; Wu Hong; Cao Chen

    2011-01-01

    Large-scale bars and minor mergers are important drivers for the secular evolution of galaxies. Based on ground-based optical images and spectra as well as ultraviolet data from the Galaxy Evolution Explorer and infrared data from the Spitzer Space Telescope, we present a multi-wavelength study of star formation properties in the barred galaxy NGC 7479, which also has obvious features of a minor merger. Using various tracers of star formation, we find that under the effects of both a stellar bar and a minor merger, star formation activity mainly takes place along the galactic bar and arms, while the star formation rate changes from the bar to the disk. With the help of spectral synthesis, we find that strong star formation took place in the bar region about 100 Myr ago, and the stellar bar might have been ∼10 Gyr old. By comparing our results with the secular evolutionary scenario from Jogee et al., we suggest that NGC 7479 is possibly in a transitional stage of secular evolution at present, and it may eventually become an earlier type galaxy or a luminous infrared galaxy. We also note that the probable minor merger event happened recently in NGC 7479, and we find two candidates for minor merger remnants.

  15. Merger mania: mergers and acquisitions in the generic drug sector from 1995 to 2016.

    Science.gov (United States)

    Gagnon, Marc-André; Volesky, Karena D

    2017-08-22

    Drug shortages and increasing generic drug prices are associated with low levels of competition. Mergers and acquisitions impact the level of competition. Record merger and acquisition activity was reported for the pharmaceutical sector in 2014/15, yet information on mergers and acquisitions in the generic drug sector are absent from the literature. This information is necessary to understand if and how such mergers and acquisitions can be a factor in drug shortages and increasing prices. Data on completed merger and acquisition deals that had a generic drug company being taken over (i.e. 'target') were extracted from Bloomberg Finance L.P. The number and announced value of deals are presented globally, for the United States, and globally excluding the United States annually from 1995 to 2016 in United States dollars. Generic drug companies comprised 9.3% of the value of all deals with pharmaceutical targets occurring from 1995 to 2016. Globally, in 1995 there were no deals, in 2014 there were 22 deals worth $1.86 billion, in 2015 there were 34 deals totalling $33.56 billion, and in 2016 there were 42 deals worth in excess of $44 billion. This substantial increase was partially attributed to Teva's 2016 acquisition of Allergan's generic drug business. The surge in mergers and acquisitions for 2015/16 was driven by deals in the United States, where they represented 89.7% of the dollar value of deals in those years. The recent blitz in mergers and acquisitions signals that the generic drug industry is undergoing a transformation, especially in the United States. This restructuring can negatively affect the level of competition that might impact prices and shortages for some products, emphasizing the importance of updating regulations and procurement policies.

  16. Financial Synergy in Mergers and Acquisitions in Saudi Arabia

    Directory of Open Access Journals (Sweden)

    Basmah Al Qudaiby (Basmah, A. Q.,

    2013-11-01

    Full Text Available Businesses today consider mergers and acquisitions a new strategy for their company’s growth. Companies aim to grow through sales’ increase, assets purchase, profits’ accumulation and market share gains. The better way for achieving these targets is by getting into either a Merger or an Acquisition. As a matter of fact, growth through mergers and acquisitions has been a critical part of the success of many companies operating in the new economy. Mergers and Acquisitions are an important factor in building up market capitalization. Based on three detailed and in depth structured interviews with major Saudi Arabian banks it has been found that, Mergers motivated by economies of scale should be approached cautiously. Companies should also approach vertical mergers cautiously because it is often difficult to gain synergy through a vertical merger and firms should also seek out mergers which allow the firm to acquire specialized knowledge. It has also been found that the firms should look for mergers that increase market power and avoid unrelated or conglomerate mergers.

  17. Synergic motives and economic success of mergers of Czech companies

    Directory of Open Access Journals (Sweden)

    Jaroslav Sedláček

    2013-01-01

    Full Text Available One of the motives for mergers and acquisitions is the synergy effect, which can take several forms. This paper tries to find out whether mergers implemented at the Czech market bring positive or negative synergies. The basis of our investigation is the database of the companies that implemented a merger within 2001–2009; out of these, the companies that published their financial statements in a digitalized form were selected. We monitored the development of six indicators characterizing the economic status of a company. The values of these indicators were compared for all participating companies before the merger and for the successor company three years after the merger. The hypotheses were formulated so that they expressed an expectation of a positive synergy brought about by mergers. However, hypothesis testing has not provided a clear result. A positive effect of a merger on the key indicator of net assets, whose growth means an increase in the accounting value of the company after the merger, has been proved for small and medium-sized companies only. The effect of mergers on the increase in indicators has been confirmed for retained earnings from past years and personal costs. Further research will concentrate on the relations between the indicators with the aim to create an integral indicator for the economic success of mergers.

  18. On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening

    Science.gov (United States)

    Leigh, N. W. C.; Geller, A. M.; McKernan, B.; Ford, K. E. S.; Mac Low, M.-M.; Bellovary, J.; Haiman, Z.; Lyra, W.; Samsing, J.; O'Dowd, M.; Kocsis, B.; Endlich, S.

    2018-03-01

    We assess the contribution of dynamical hardening by direct three-body scattering interactions to the rate of stellar-mass black hole binary (BHB) mergers in galactic nuclei. We derive an analytic model for the single-binary encounter rate in a nucleus with spherical and disc components hosting a super-massive black hole (SMBH). We determine the total number of encounters NGW needed to harden a BHB to the point that inspiral due to gravitational wave emission occurs before the next three-body scattering event. This is done independently for both the spherical and disc components. Using a Monte Carlo approach, we refine our calculations for NGW to include gravitational wave emission between scattering events. For astrophysically plausible models, we find that typically NGW ≲ 10. We find two separate regimes for the efficient dynamical hardening of BHBs: (1) spherical star clusters with high central densities, low-velocity dispersions, and no significant Keplerian component and (2) migration traps in discs around SMBHs lacking any significant spherical stellar component in the vicinity of the migration trap, which is expected due to effective orbital inclination reduction of any spherical population by the disc. We also find a weak correlation between the ratio of the second-order velocity moment to velocity dispersion in galactic nuclei and the rate of BHB mergers, where this ratio is a proxy for the ratio between the rotation- and dispersion-supported components. Because discs enforce planar interactions that are efficient in hardening BHBs, particularly in migration traps, they have high merger rates that can contribute significantly to the rate of BHB mergers detected by the advanced Laser Interferometer Gravitational-Wave Observatory.

  19. Radio stars

    International Nuclear Information System (INIS)

    Hjellming, R.M.

    1976-01-01

    Any discussion of the radio emission from stars should begin by emphasizing certain unique problems. First of all, one must clarify a semantic confusion introduced into radio astronomy in the late 1950's when most new radio sources were described as radio stars. All of these early 'radio stars' were eventually identified with other galactic and extra-galactic objects. The study of true radio stars, where the radio emission is produced in the atmosphere of a star, began only in the 1960's. Most of the work on the subject has, in fact, been carried out in only the last few years. Because the real information about radio stars is quite new, it is not surprising that major aspects of the subject are not at all understood. For this reason this paper is organized mainly around three questions: what is the available observational information; what physical processes seem to be involved; and what working hypotheses look potentially fruitful. (Auth.)

  20. Shooting stars

    International Nuclear Information System (INIS)

    Maurette, M.; Hammer, C.

    1985-01-01

    A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is this article object; orbit gathering projects are also presented [fr

  1. Possible role of magnetic reconnection in the electromagnetic counterpart of binary black hole merger

    Science.gov (United States)

    Fraschetti, F.

    2018-04-01

    We propose a qualitative scenario to interpret the argued association between the direct measurement of the gravitational wave event GW150914 by Laser Interferometer Gravitational Wave Observatory (LIGO)-Virgo collaborations and the hard X-ray transient detected by Fermi-Gamma-ray Burst Monitor (GBM) 0.4 sec after. In a binary system of two gravitationally collapsing objects with a non-vanishing electric charge, the compenetration of the two magnetospheres occurring during the coalescence, through magnetic reconnection, produces a highly collimated relativistic outflow that becomes optically thin and shines in the GBM field of view. We propose that this process should be expected as a commonplace in the future joint gravitational/electromagnetic detections and, in case of neutron star-neutron star merger event, might lead to detectable X- or γ-ray precursors to, or transients associated with, the gravitational bursts.

  2. On the origin of high-velocity runaway stars

    Science.gov (United States)

    Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

    2009-06-01

    We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50-100Msolar star or a more massive one, formed through runaway mergers of ordinary stars in the core of a young massive star cluster). In this process, one of the binary components becomes gravitationally bound to the very massive star, while the second one is ejected, sometimes with a high speed. We performed three-body scattering experiments and found that early B-type stars (the progenitors of the majority of neutron stars) can be ejected with velocities of >~200-400kms-1 (typical of pulsars), while 3-4Msolar stars can attain velocities of >~300-400kms-1 (typical of the bound population of halo late B-type stars). We also found that the ejected stars can occasionally attain velocities exceeding the Milky Ways's escape velocity.

  3. THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?

    Energy Technology Data Exchange (ETDEWEB)

    Clayton, Geoffrey C.; Andrews, J. E. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Sugerman, Ben E. K. [Department of Physics and Astronomy, Goucher College, 1021 Dulaney Valley Rd., Baltimore, MD 21204 (United States); Adam Stanford, S. [IGPP, Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Whitney, B. A. [Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO 80301 (United States); Honor, J.; Babler, B. [Department of Astronomy, 475 North Charter St., University of Wisconsin, Madison, WI 53706 (United States); Barlow, M. J. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Gordon, K. D.; Bond, Howard E.; Matsuura, M. [STScI, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Geballe, T. R. [Gemini Observatory, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); De Marco, O. [Department of Physics, Macquarie University, Sydney, NSW 2109 (Australia); Lawson, W. A. [School of PEMS, University of New South Wales, ADFA, P.O. Box 7916, Canberra, ACT 2610 (Australia); Sibthorpe, B. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Olofsson, G. [Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, SE-10691 Stockholm (Sweden); Polehampton, E. [Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot OX11 0QX (United Kingdom); Gomez, H. L.; Hargrave, P. C. [School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, Wales CF24 3YB (United Kingdom); Ivison, R. J., E-mail: gclayton@phys.lsu.edu, E-mail: jandrews@phys.lsu.edu, E-mail: ben.sugerman@goucher.edu, E-mail: stanford@physics.ucdavis.edu, E-mail: bwhitney@spacescience.org, E-mail: jhonor@astro.wisc.edu, E-mail: brian@astro.wisc.edu, E-mail: mjb@star.ucl.ac.uk [UK Astronomy Technology Centre, ROE, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); and others

    2011-12-10

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 {mu}m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 {mu}m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10{sup -4} and 2 M{sub Sun }, respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  4. THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?

    International Nuclear Information System (INIS)

    Clayton, Geoffrey C.; Andrews, J. E.; Sugerman, Ben E. K.; Adam Stanford, S.; Whitney, B. A.; Honor, J.; Babler, B.; Barlow, M. J.; Gordon, K. D.; Bond, Howard E.; Matsuura, M.; Geballe, T. R.; De Marco, O.; Lawson, W. A.; Sibthorpe, B.; Olofsson, G.; Polehampton, E.; Gomez, H. L.; Hargrave, P. C.; Ivison, R. J.

    2011-01-01

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 μm with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 μm. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10 –4 and 2 M ☉ , respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  5. The influence of massive black hole binaries on the morphology of merger remnants

    Science.gov (United States)

    Bortolas, E.; Gualandris, A.; Dotti, M.; Read, J. I.

    2018-06-01

    Massive black hole (MBH) binaries, formed as a result of galaxy mergers, are expected to harden by dynamical friction and three-body stellar scatterings, until emission of gravitational waves (GWs) leads to their final coalescence. According to recent simulations, MBH binaries can efficiently harden via stellar encounters only when the host geometry is triaxial, even if only modestly, as angular momentum diffusion allows an efficient repopulation of the binary loss cone. In this paper, we carry out a suite of N-body simulations of equal-mass galaxy collisions, varying the initial orbits and density profiles for the merging galaxies and running simulations both with and without central MBHs. We find that the presence of an MBH binary in the remnant makes the system nearly oblate, aligned with the galaxy merger plane, within a radius enclosing 100 MBH masses. We never find binary hosts to be prolate on any scale. The decaying MBHs slightly enhance the tangential anisotropy in the centre of the remnant due to angular momentum injection and the slingshot ejection of stars on nearly radial orbits. This latter effect results in about 1 per cent of the remnant stars being expelled from the galactic nucleus. Finally, we do not find any strong connection between the remnant morphology and the binary hardening rate, which depends only on the inner density slope of the remnant galaxy. Our results suggest that MBH binaries are able to coalesce within a few Gyr, even if the binary is found to partially erase the merger-induced triaxiality from the remnant.

  6. Dynamics of merging: post-merger mixing and relaxation of an Illustris galaxy

    Science.gov (United States)

    Young, Anthony M.; Williams, Liliya L. R.; Hjorth, Jens

    2018-02-01

    During the merger of two galaxies, the resulting system undergoes violent relaxation and seeks stable equilibrium. However, the details of this evolution are not fully understood. Using Illustris simulation, we probe two physically related processes, mixing and relaxation. Though the two are driven by the same dynamics—global time-varying potential for the energy, and torques caused by asymmetries for angular momentum—we measure them differently. We define mixing as the redistribution of energy and angular momentum between particles of the two merging galaxies. We assess the degree of mixing as the difference between the shapes of their energy distributions, N(E)s, and their angular momentum distributions, N(L2)s. We find that the difference is decreasing with time, indicating mixing. To measure relaxation, we compare N(E) of the newly merged system to N(E) of a theoretical prediction for relaxed collisionless systems, DARKexp, and witness the system becoming more relaxed, in the sense that N(E) approaches DARKexp N(E). Because the dynamics driving mixing and relaxation are the same, the timescale is similar for both. We measure two sequential timescales: a rapid, 1 Gyr phase after the initial merger, during which the difference in N(E) of the two merging halos decreases by ~ 80%, followed by a slow phase, when the difference decreases by ~ 50% over ~ 8.5 Gyrs. This is a direct measurement of the relaxation timescale. Our work also draws attention to the fact that when a galaxy has reached Jeans equilibrium it may not yet have reached a fully relaxed state given by DARKexp, in that it retains information about its past history. This manifests itself most strongly in stars being centrally concentrated. We argue that it is particularly difficult for stars, and other tightly bound particles, to mix because they have less time to be influenced by the fluctuating potential, even across multiple merger events.

  7. Mergers and acquisitions for the radiologist.

    Science.gov (United States)

    Fleishon, Howard B

    2008-05-01

    In 2006 and the first half of 2007, the rapid pace of global activity contributed to the popularity of mergers and acquisitions (M&A). In fact, the medical imaging industry has a significant history in M&A as well. Along with the expectation of continued growth in medical imaging utilization and other industry trends, radiologists may become more involved in M&A transactions. There is little in the radiology literature dealing with the logistics and pitfalls of M&A. This article is an introduction for radiologists who might consider buying or selling their practices or merging with strategic partners. Although there are significant differences in the approaches of buy or sell situations compared with mergers, they do share several concepts that are outlined. One key to success in M&A transactions is the "process" or approach, which is described with some practical guidelines. Some basic terms and suggestions are also presented for reference.

  8. Do Municipal Mergers Improve Fiscal Outcomes?

    DEFF Research Database (Denmark)

    Hansen, Sune Welling; Houlberg, Kurt; Holm Pedersen, Lene

    2014-01-01

    Improved fiscal management is a frequent justification for promoting boundary consolidations. However, whether or not this is actually the case is rarely placed under rigorous empirical scrutiny. Hence, this article investigates if fiscal outcomes are improved when municipalities are merged....... The basic argument is that the conceptualisation of fiscal management in political science is often too narrow as it focuses on the budget and pays hardly any attention to balances in the final accounts and debts – elements of management which are central to policy making. On this background, the causal...... relationship between municipal mergers and fiscal outcomes is analysed. Measured on the balance between revenues and expenses, liquid assets and debts, municipal mergers improve the fiscal outcomes of the municipalities in a five-year perspective, although the pre-reform effects tend to be negative...

  9. The importance of partnerships, mergers and acquisitions

    Energy Technology Data Exchange (ETDEWEB)

    Trabandt, C.A. [Merrill Lynch, New York, NY (United States)

    1998-09-01

    An overview of the electric utility industry was presented. The main factors driving mergers and acquisitions in the industry were identified as being consolidation, disaggregation, convergence and international expansion. To prove the point, statistics from recent merger and acquisition transactions in the U.S. were presented. The importance of disaggregation of the utility business and convergence as the major themes of the electricity and natural gas industries were demonstrated. They are driven by a new competitive marketplace and fewer regulations. The driving forces behind them were explained, buttressing the arguments with recent statistics reflecting an upsurge in convergence transactions. Significant opportunities abroad and recent foreign acquisitions by U. S. utilities were also reviewed. With regard to convergence, it was shown to be occurring in both the generation/wholesale and distribution/retail marketing segment of the electric power industry. 3 figs.

  10. Estimating the potential gains from mergers

    DEFF Research Database (Denmark)

    Bogetoft, Peter; Wang, Dexiang

    2005-01-01

    We introduce simple production economic models to estimate the potential gains from mergers. We decompose the gains into technical ef¿ciency, size (scale) and harmony (mix) gains, and we discuss alternative ways to capture these gains. We propose to approximate the production processes using...... the non-parametric. Data Envelopment Analysis (DEA) approach, and we use the resulting operational approach to estimate the potential gains from merging agricultural extension of¿ces in Denmark....

  11. Merger negotiations with stock market feedback

    OpenAIRE

    Betton, Sandra; Eckbo, B. Espen; Thompson, Rex; Thorburn, Karin S.

    2011-01-01

    Merger negotiations routinely occur amidst economically significant a target stock price runups. Since the source of the runup is unobservable (is it a target stand-alone value change and/or deal anticipation?), feeding the runup back into the offer price risks "paying twice" for the target shares. We present a novel structural empirical analysis of this runup feedback hypothesis. We show that rational deal anticipation implies a nonlinear relationship between the runup and the offer price ma...

  12. Maximum Redshift of Gravitational Wave Merger Events

    Science.gov (United States)

    Koushiappas, Savvas M.; Loeb, Abraham

    2017-12-01

    Future generations of gravitational wave detectors will have the sensitivity to detect gravitational wave events at redshifts far beyond any detectable electromagnetic sources. We show that if the observed event rate is greater than one event per year at redshifts z ≥40 , then the probability distribution of primordial density fluctuations must be significantly non-Gaussian or the events originate from primordial black holes. The nature of the excess events can be determined from the redshift distribution of the merger rate.

  13. A scoreboard of mergers and acquisitions

    Energy Technology Data Exchange (ETDEWEB)

    Parent, L.V

    1989-08-01

    In the late 70s and early 80s when market growth was not a viable alternative and price deregulation was imminent, new strategies were sought that would provide some basis for survival in a deregulated environment, and merger/acquisition strategy took on new significance. According to the author, eight mega gas pipe line companies have evolved. The strategic objectives behind these merges is analyzed.

  14. NGC 404: A REJUVENATED LENTICULAR GALAXY ON A MERGER-INDUCED, BLUEWARD EXCURSION INTO THE GREEN VALLEY

    International Nuclear Information System (INIS)

    Thilker, David A.; Bianchi, Luciana; Schiminovich, David; Gil de Paz, Armando; Seibert, Mark; Madore, Barry F.; Wyder, Ted; Barlow, Tom; Conrow, Tim; Forster, Karl; Friedman, Peter; Martin, Chris; Morrissey, Patrick; Small, Todd; Rich, R. Michael; Yi, Sukyoung; Neff, Susan

    2010-01-01

    We have discovered recent star formation in the outermost portion ((1-4) x R 25 ) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's H I ring (formed by a merger event according to del RIo et al.), even though the average gas density is dynamically subcritical. Archival Hubble Space Telescope imaging reveals resolved upper main-sequence stars and conclusively demonstrates that the UV light originates from recent star formation activity. We present FUV, NUV radial surface brightness profiles, and integrated magnitudes for NGC 404. Within the ring, the average star formation rate (SFR) surface density (Σ SFR ) is ∼2.2 x 10 -5 M sun yr -1 kpc -2 . Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 x 10 -3 M sun yr -1 . The gas consumption timescale, assuming a constant SFR and no gas recycling, is several times the age of the universe. In the context of the UV-optical galaxy color-magnitude diagram, the presence of the star-forming H I ring places NGC 404 in the green valley separating the red and blue sequences. The rejuvenated lenticular galaxy has experienced a merger-induced, disk-building excursion away from the red sequence toward bluer colors, where it may evolve quiescently or (if appropriately triggered) experience a burst capable of placing it on the blue/star-forming sequence for up to ∼1 Gyr. The green valley galaxy population is heterogeneous, with most systems transitioning from blue to red but others evolving in the opposite sense due to acquisition of fresh gas through various channels.

  15. Gravitational waves from primordial black hole mergers

    Energy Technology Data Exchange (ETDEWEB)

    Raidal, Martti; Vaskonen, Ville; Veermäe, Hardi, E-mail: martti.raidal@cern.ch, E-mail: ville.vaskonen@kbfi.ee, E-mail: hardi.veermae@cern.ch [NICPB, Rävala 10, 10143 Tallinn (Estonia)

    2017-09-01

    We study the production of primordial black hole (PBH) binaries and the resulting merger rate, accounting for an extended PBH mass function and the possibility of a clustered spatial distribution. Under the hypothesis that the gravitational wave events observed by LIGO were caused by PBH mergers, we show that it is possible to satisfy all present constraints on the PBH abundance, and find the viable parameter range for the lognormal PBH mass function. The non-observation of a gravitational wave background allows us to derive constraints on the fraction of dark matter in PBHs, which are stronger than any other current constraint in the PBH mass range 0.5−30 M {sub ⊙}. We show that the predicted gravitational wave background can be observed by the coming runs of LIGO, and its non-observation would indicate that the observed events are not of primordial origin. As the PBH mergers convert matter into radiation, they may have interesting cosmological implications, for example in the context of relieving the tension between high and low redshift measurements of the Hubble constant. However, we find that these effects are suppressed as, after recombination, no more that 1% of dark matter can be converted into gravitational waves.

  16. GRAVITATIONAL MEMORY IN BINARY BLACK HOLE MERGERS

    International Nuclear Information System (INIS)

    Pollney, Denis; Reisswig, Christian

    2011-01-01

    In addition to the dominant oscillatory gravitational wave signals produced during binary inspirals, a non-oscillatory component arises from the nonlinear 'memory' effect, sourced by the emitted gravitational radiation. The memory grows significantly during the late-inspiral and merger, modifying the signal by an almost step-function profile, and making it difficult to model by approximate methods. We use numerical evolutions of binary black holes (BHs) to evaluate the nonlinear memory during late-inspiral, merger, and ringdown. We identify two main components of the signal: the monotonically growing portion corresponding to the memory, and an oscillatory part which sets in roughly at the time of merger and is due to the BH ringdown. Counterintuitively, the ringdown is most prominent for models with the lowest total spin. Thus, the case of maximally spinning BHs anti-aligned to the orbital angular momentum exhibits the highest signal-to-noise ratio (S/N) for interferometric detectors. The largest memory offset, however, occurs for highly spinning BHs, with an estimated value of h tot 20 ≅ 0.24 in the maximally spinning case. These results are central to determining the detectability of nonlinear memory through pulsar timing array measurements.

  17. Simulations of inspiraling and merging double neutron stars using the Spectral Einstein Code

    Science.gov (United States)

    Haas, Roland; Ott, Christian D.; Szilagyi, Bela; Kaplan, Jeffrey D.; Lippuner, Jonas; Scheel, Mark A.; Barkett, Kevin; Muhlberger, Curran D.; Dietrich, Tim; Duez, Matthew D.; Foucart, Francois; Pfeiffer, Harald P.; Kidder, Lawrence E.; Teukolsky, Saul A.

    2016-06-01

    We present results on the inspiral, merger, and postmerger evolution of a neutron star-neutron star (NSNS) system. Our results are obtained using the hybrid pseudospectral-finite volume Spectral Einstein Code (SpEC). To test our numerical methods, we evolve an equal-mass system for ≈22 orbits before merger. This waveform is the longest waveform obtained from fully general-relativistic simulations for NSNSs to date. Such long (and accurate) numerical waveforms are required to further improve semianalytical models used in gravitational wave data analysis, for example, the effective one body models. We discuss in detail the improvements to SpEC's ability to simulate NSNS mergers, in particular mesh refined grids to better resolve the merger and postmerger phases. We provide a set of consistency checks and compare our results to NSNS merger simulations with the independent bam code. We find agreement between them, which increases confidence in results obtained with either code. This work paves the way for future studies using long waveforms and more complex microphysical descriptions of neutron star matter in SpEC.

  18. Merger and Innovation Incentives in a Differentiated Industry

    OpenAIRE

    Kesavayuth, Dusanee; Lee, Sang-Ho; Zikos, Vasileios

    2017-01-01

    In this paper, we consider a duopoly with product differentiation and examine the interaction between merger and innovation incentives. The analysis reveals that a merger tends to discourage innovation, unless the investment cost is sufficiently low. This result holds whether or not side payments between firms are allowed. When side payments are permitted, a bilateral merger-to-monopoly is always profitable, a standard result in the literature. When side payments are not permitted, however, w...

  19. The benefit of mergers and taking-overs

    International Nuclear Information System (INIS)

    Nillesen, P.H.L.; Keats, K.; Pollitt, M.

    2001-01-01

    Electricity companies can realize considerable efficiency benefits through mergers by using management skills of a more efficient company and the resulting changed mix of inputs. In this article a pattern of thought is introduced by means of which cost savings of mergers can be identified in a strategic and scientific way. Such a way of thinking can be applied, e.g. in a cash flow analysis, in the valuation of companies and in the merger and taking-over process. 7 refs

  20. VersaCold: Analysis of Change Management in Mergers & Acquisitions

    OpenAIRE

    Eslami, Sara

    2011-01-01

    Many firms use mergers and acquisitions as a corporate strategy to increase shareholder value. Therefore, understanding such a widely exercised strategy and its implications on corporate change would be critical for organizations that wish to pursue this strategy. This study provides an in depth review of mergers and acquisitions and introduces best practices for managing changes that result from mergers and acquisitions. Next, the concepts are applied to two cases of acquisitions in VersaCol...

  1. Strategy and Tactics of International Mergers and Acquisitions

    Directory of Open Access Journals (Sweden)

    Denys Kiriakov

    2011-12-01

    Full Text Available The article reviews contemporary strategy and tactics issues in terms of international mergers and acquisitions, along with displaying cyclical waves of mergers and acquisitions over the last century as well as motivation thereof. Five strategies adhered to by international companies initiating conclusion of such agreements as well as challenges accompanying execution thereof have been analyzed. Modern strategic and tactical tools of international mergers and acquisitions process management have been researched on exemplary buyer (a corporation case-study.

  2. Value Creation through ICT Integration in Merger & Acquisition Processes

    DEFF Research Database (Denmark)

    Holm Larsen, Michael

    2005-01-01

    As deals are becoming more complex, and as technology, and the people supporting it, are becoming key drivers of merger and acquisition processes, planning of information and communication technologies in early stages of