WorldWideScience

Sample records for neutron star mass

  1. Nuclear Masses and Neutron Stars

    CERN Document Server

    Kreim, Susanne; Lunney, David; Schaffner-Bielich, Jürgen

    2013-01-01

    Precision mass spectrometry of neutron-rich nuclei is of great relevance for astrophysics. Masses of exotic nuclides impose constraints on models for the nuclear interaction and thus affect the description of the equation of state of nuclear matter, which can be extended to describe neutron-star matter. With knowledge of the masses of nuclides near shell closures, one can also derive the neutron-star crustal composition. The Penning-trap mass spectrometer ISOLTRAP at CERN-ISOLDE has recently achieved a breakthrough measuring the mass of 82Zn, which allowed constraining neutron-star crust composition to deeper layers (Wolf et al., PRL 110, 2013). We perform a more detailed study on the sequence of nuclei in the outer crust of neutron stars with input from different nuclear models to illustrate the sensitivity to masses and the robustness of neutron-star models. The dominant role of the N=50 and N=82 closed neutron shells for the crustal composition is confirmed.

  2. The masses of neutron stars

    CERN Document Server

    Horvath, J E

    2016-01-01

    We present in this article an overview of the problem of neutron star masses. After a brief appraisal of the methods employed to determine the masses of neutron stars in binary systems, the existing sample of measured masses is presented, with a highlight on some very well-determined cases. We discuss the analysis made to uncover the underlying distribution and a few robust results that stand out from them. The issues related to some particular groups of neutron stars originated from different channels of stellar evolution are shown. Our conclusions are that last century's paradigm that there a single, $1.4 M_{\\odot}$ scale is too simple. A bimodal or even more complex distribution is actually present. It is confirmed that some neutron stars have masses of $\\sim 2 M_{\\odot}$, and, while there is still no firm conclusion on the maximum and minimum values produced in nature, the field has entered a mature stage in which all these and related questions can soon be given an answer.

  3. ON THE MASSES OF NEUTRON-STARS

    NARCIS (Netherlands)

    VANKERKWIJK, MH; VANPARADIJS, J; ZUIDERWIJK, EJ

    1995-01-01

    We analyze the currently available observations of X-ray binaries in a consistent way, to re-determine the masses of the neutron stars in these systems. In particular, our attention is focussed on a realistic and consistent assessment of observational uncertainties and sources of systematic error. C

  4. Mass ejection in neutron star mergers

    Science.gov (United States)

    Rosswog, S.; Liebendörfer, M.; Thielemann, F.-K.; Davies, M. B.; Benz, W.; Piran, T.

    1999-01-01

    We present the results of 3D Newtonian SPH simulations of the merger of a neutron star binary. The microscopic properties of matter are described by the physical equation of state of Lattimer and Swesty (LS-EOS). To check the model dependence of the results we vary the resolution ( ~ 21000 and ~ 50000 particles), the equation of state (stiff and soft polytropes), the artificial viscosity scheme, the stellar masses, we include neutrinos (free-streaming limit), switch off the gravitational backreaction force, and vary the initial stellar spins. In addition we test the influence of the initial configuration, i.e. spherical stars versus corotating equilibrium configurations. The final matter distribution consists of a rapidly spinning central object with 2.5 to 3.1 Msun of baryonic mass that probably collapses to a black hole, a thick disk of 0.1 to 0.3 Msun and an extended low density region. In the case of corotation this low density material forms spiral arms that expand explosively due to an increase of the adiabatic exponent and the release of nuclear binding energy in the case of the LS-EOS, but remain narrow and well defined for the stiff polytropic equation of state. The main and new result is that for the realistic LS-EOS, depending on the initial spin, between 4*10(-3) and 4*10(-2) Msun of material become unbound. If, as suggested, large parts of this matter consist of r-process nuclei, neutron star mergers could account for the whole observed r-process material in the Galaxy.

  5. Millisecond phenomena in mass accreting neutron stars

    NARCIS (Netherlands)

    van der Klis, M.; Cohen, L.

    2007-01-01

    The past twelve years have seen the discovery, with NASA's Rossi X-ray Timing Explorer (RXTE), of several long-predicted phenomena associated with the accretion of matter onto a neutron star in a binary (double) star system. These phenomena are observed in the strong X-ray emission produced by these

  6. Observational constraints on neutron star masses and radii

    Energy Technology Data Exchange (ETDEWEB)

    Coleman Miller, M. [University of Maryland, Department of Astronomy and Joint Space-Science Institute, College Park, MD (United States); Lamb, Frederick K. [University of Illinois at Urbana-Champaign, Center for Theoretical Astrophysics and Department of Physics, Urbana, IL (United States); University of Illinois at Urbana-Champaign, Department of Astronomy, Urbana, IL (United States)

    2016-03-15

    Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star - black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method. (orig.)

  7. Observational Constraints on Neutron Star Masses and Radii

    CERN Document Server

    Miller, M Coleman

    2016-01-01

    Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star -- black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method...

  8. Rotating neutron stars with exotic cores: masses, radii, stability

    Energy Technology Data Exchange (ETDEWEB)

    Haensel, P.; Bejger, M.; Fortin, M.; Zdunik, L. [Polish Academy of Sciences, N. Copernicus Astronomical Center, Warszawa (Poland)

    2016-03-15

    A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716Hz) and the maximum measured mass (2M {sub CircleDot}). The present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered. (orig.)

  9. Evolution of low mass close binary systems with a neutron star: its dependence with the initial neutron star mass

    CERN Document Server

    De Vito, M A

    2012-01-01

    We construct a set of binary evolutionary sequences for systems composed by a normal, solar composition, donor star together with a neutron star. We consider a variety of masses for each star as well as for the initial orbital period corresponding to systems that evolve to ultra-compact or millisecond pulsar-helium white dwarf pairs. Specifically, we select a set of donor star masses of 0.50, 0.65, 0.80, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 3.00, and 3.50 solar masses, whereas for the accreting neutron star we consider initial masses values of 0.8, 1.0, 1.2, and 1.4 solar masses. The considered initial orbital period interval ranges from 0.5 to 12 days. It is found that the evolution of systems, with fixed initial values for the orbital period and the mass of the normal donor star, heavily depends upon the mass of the neutron star. In some cases, varying the initial value of the neutron star mass, we obtain evolved configurations ranging from ultra-compact to widely separated objects. We also analyse the...

  10. Neutron Star Magnetic Field as for Nonzero Photon Mass

    Institute of Scientific and Technical Information of China (English)

    WANG Qing-Wu; L(U) Xiao-Fu

    2005-01-01

    We investigate the neutron star magnetic field by the relative mean-field theory, where the photon effective mass depending on baryon density of charged particles is nonzero. This field is produced by star itself, which is the function of baryon density. The result fits the observations.

  11. Formation scenarios and mass-radius relation for neutron stars

    CERN Document Server

    Zdunik, J L

    2011-01-01

    Neutron star crust, formed via accretion of matter from a companion in a low-mass X-ray binary (LMXB), has an equation of state (EOS) stiffer than that of catalyzed matter. At a given neutron star mass, M, the radius of a star with an accreted crust is therefore larger, by DR(M), than for usually considered star built of catalyzed matter. Using a compressible liquid drop model of nuclei, we calculate, within the one-component plasma approximation, the EOSs corresponding to different nuclear compositions of ashes of X-ray bursts in LMXB. These EOSs are then applied for studying the effect of different formation scenarios on the neutron-star mass-radius relation. Assuming the SLy EOS for neutron star's liquid core, derived by Douchin & Haensel (2001), we find that at M=1.4 M_sun the star with accreted crust has a radius more than 100 m larger that for the crust of catalyzed matter. Using smallness of the crust mass compared to M, we derive a formula that relates DR(M) to the difference in the crust EOS. Thi...

  12. Rotating neutron stars with exotic cores: masses, radii, stability

    CERN Document Server

    Haensel, P; Fortin, M; Zdunik, J L

    2016-01-01

    A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency is 716 Hz and the maximum measured mass is $2\\;{\\rm M}_\\odot$. Present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a fi...

  13. The Masses and Spins of Neutron Stars and Stellar-Mass Black Holes

    CERN Document Server

    Miller, M Coleman

    2014-01-01

    Stellar-mass black holes and neutron stars represent extremes in gravity, density, and magnetic fields. They therefore serve as key objects in the study of multiple frontiers of physics. In addition, their origin (mainly in core-collapse supernovae) and evolution (via accretion or, for neutron stars, magnetic spindown and reconfiguration) touch upon multiple open issues in astrophysics. In this review, we discuss current mass and spin measurements and their reliability for neutron stars and stellar-mass black holes, as well as the overall importance of spins and masses for compact object astrophysics. Current masses are obtained primarily through electromagnetic observations of binaries, although future microlensing observations promise to enhance our understanding substantially. The spins of neutron stars are straightforward to measure for pulsars, but the birth spins of neutron stars are more difficult to determine. In contrast, even the current spins of stellar-mass black holes are challenging to measure. ...

  14. Dynamical mass ejection from black hole-neutron star binaries

    CERN Document Server

    Kyutoku, Koutarou; Okawa, Hirotada; Shibata, Masaru; Taniguchi, Keisuke

    2015-01-01

    We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10deg--20deg and often sweeps only a half of the plane. The ejecta mass can be as large as ~0.1M_sun, and the velocity is subrelativistic with ~0.2--0.3c for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) becomes high and the ejecta velocity is large when the binary mass ratio is large, i.e., the black hole is massive. The remnant black hole-disk system receives a kick velocity of O(100)km/s due to the ejecta linear...

  15. Neutron Star Mass-Radius Constraints using Evolutionary Optimization

    CERN Document Server

    Stevens, A L; Leahy, D A; Morsink, S M

    2016-01-01

    The equation of state of cold supra-nuclear-density matter, such as in neutron stars, is an open question in astrophysics. A promising method for constraining the neutron star equation of state is modelling pulse profiles of thermonuclear X-ray burst oscillations from hotspots on accreting neutron stars. The pulse profiles, constructed using spherical and oblate neutron star models, are comparable to what would be observed by a next-generation X-ray timing instrument like ASTROSAT, NICER, or LOFT. In this paper we showcase the use of an evolutionary optimization algorithm to fit pulse profiles to determine the best-fitting masses and radii. By fitting synthetic data, we assess how well the optimization algorithm can recover the input parameters. Multiple Poisson realizations of the synthetic pulse profiles were fitted with the Ferret Genetic Algorithm to analyze both statistical and systematic uncertainty, and to explore how the goodness-of-fit depends on the input parameters. The best-determined parameter is...

  16. Masses, Radii, and the Equation of State of Neutron Stars

    Science.gov (United States)

    Özel, Feryal; Freire, Paulo

    2016-09-01

    We summarize our current knowledge of neutron-star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the past few years, leading to a large number of mass measurements. These discoveries show that the neutron-star mass distribution is much wider than previously thought, with three known pulsars now firmly in the 1.9-2.0-M⊙ mass range. For radii, large, high-quality data sets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 10-11.5-km range and shrinking their uncertainties, owing to a better understanding of the sources of systematic errors. The combination of the massive-neutron-star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties of cold nuclear matter at densities higher than that of the atomic nucleus, a major unsolved problem in modern physics.

  17. Masses, Radii, and Equation of State of Neutron Stars

    CERN Document Server

    Ozel, Feryal

    2016-01-01

    We summarize our current knowledge of neutron star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the last few years, leading to a large number of mass measurements. These discoveries show that the neutron star mass distribution is much wider than previously thought, with 3 known pulsars now firmly in the 1.9-2.0 Msun mass range. For radii, large, high quality datasets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 9.9-11.2 km range and shrinking their uncertainties due to a better understanding of the sources of systematic errors. The combination of the massive neutron star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties...

  18. Neutron star kicks and their relationship to supernovae ejecta mass

    Science.gov (United States)

    Bray, J. C.; Eldridge, J. J.

    2016-10-01

    We propose a simple model to explain the velocity of young neutron stars. We attempt to confirm a relationship between the amount of mass ejected in the formation of the neutron star and the `kick' velocity imparted to the compact remnant resulting from the process. We assume that the velocity is given by vkick = α (Mejecta/Mremnant) + β . To test this simple relationship, we use the BPASS (Binary Population and Spectral Synthesis) code to create stellar population models from both single and binary star evolutionary pathways. We then use our Remnant Ejecta and Progenitor Explosion Relationship (REAPER) code to apply different α and β values, and three different `kick' orientations then record the resulting velocity probability distributions. We find that while a single star population provides a poor fit to the observational data, the binary population provides an excellent fit. Values of α = 70 km s-1 and β = 110 km s-1 reproduce the Hobbs et al. observed two-dimensional velocities, and α = 70 km s-1 and β = 120 km s-1 reproduce their inferred three-dimensional velocity distribution for nearby single neutron stars with ages less than 3 Myr. After testing isotropic, spin-axis aligned and orthogonal to spin-axis `kick' orientations, we find no statistical preference for a `kick' orientation. While ejecta mass cannot be the only factor that determines the velocity of supernova compact remnants, we suggest that it is a significant contributor and that the ejecta-based `kick' should replace the Maxwell-Boltzmann velocity distribution currently used in many population synthesis codes.

  19. Neutron Star Kicks and their Relationship to Supernovae Ejecta Mass

    CERN Document Server

    Bray, J C

    2016-01-01

    We propose a simple model to explain the velocity of young neutron stars. We attempt to confirm a relationship between the amount of mass ejected in the formation of the neutron star and the `kick' velocity imparted to the compact remnant resulting from the process. We assume the velocity is given by $v_{\\rm kick}=\\alpha\\,(M_{\\rm ejecta} / M_{\\rm remnant}) + \\beta\\,$. To test this simple relationship we use the BPASS (Binary Population and Spectral Synthesis) code to create stellar population models from both single and binary star evolutionary pathways. We then use our Remnant Ejecta and Progenitor Explosion Relationship (REAPER) code to apply different $\\alpha$ and $\\beta$ values and three different `kick' orientations then record the resulting velocity probability distributions. We find that while a single star population provides a poor fit to the observational data, the binary population provides an excellent fit. Values of $\\alpha=70\\, {\\rm km\\,s^{-1}}$ and $\\beta=110\\,{\\rm km\\,s^{-1}}$ reproduce the \\c...

  20. Dynamical Mass Ejection from Binary Neutron Star Mergers

    CERN Document Server

    Radice, David; Lippuner, Jonas; Roberts, Luke F; Ott, Christian D; Rezzolla, Luciano

    2016-01-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad $\\sim 60^\\circ$ angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. This is the effect of the strong tidal torques exerted on the neutron stars during their ...

  1. The masses and spins of neutron stars and stellar-mass black holes

    Energy Technology Data Exchange (ETDEWEB)

    Miller, M. Coleman, E-mail: miller@astro.umd.edu [University of Maryland, Department of Astronomy and Joint Space-Science Institute, College Park, MD 20742-2421 (United States); Miller, Jon M. [University of Michigan, Department of Astronomy, 500 Church Street, Ann Arbor, MI 48109-1042 (United States)

    2015-01-10

    Stellar-mass black holes and neutron stars represent extremes in gravity, density, and magnetic fields. They therefore serve as key objects in the study of multiple frontiers of physics. In addition, their origin (mainly in core-collapse supernovae) and evolution (via accretion or, for neutron stars, magnetic spindown and reconfiguration) touch upon multiple open issues in astrophysics. In this review, we discuss current mass and spin measurements and their reliability for neutron stars and stellar-mass black holes, as well as the overall importance of spins and masses for compact object astrophysics. Current masses are obtained primarily through electromagnetic observations of binaries, although future microlensing observations promise to enhance our understanding substantially. The spins of neutron stars are straightforward to measure for pulsars, but the birth spins of neutron stars are more difficult to determine. In contrast, even the current spins of stellar-mass black holes are challenging to measure. As we discuss, major inroads have been made in black hole spin estimates via analysis of iron lines and continuum emission, with reasonable agreement when both types of estimate are possible for individual objects, and future X-ray polarization measurements may provide additional independent information. We conclude by exploring the exciting prospects for mass and spin measurements from future gravitational wave detections, which are expected to revolutionize our understanding of strong gravity and compact objects.

  2. Measuring Neutron Star Mass and Radius with Three Mass-Radius Relations

    CERN Document Server

    Zhang, C M; Kojima, Y; Chang, H K; Xu, R X; Li, X D; Zhang, B; Kiziltan, B

    2006-01-01

    We propose to determine the mass and the radius of a neutron star (NS) using three measurable mass-radius relationships, namely the ``apparent'' radius inferred from neutron star thermal emission, the gravitational redshift inferred from the absorption lines, as well as the averaged stellar mass density inferred from the orbital Keplerian frequency derived from the kilohertz quasi periodic oscillation (kHz QPO) data. We apply the method to constrain the NS mass and the radius of the X-ray sources, 1E 1207.4-5209, Aql X-1 and EXO 0748-676.

  3. Formation and Evolution of Neutron Star Binaries: Masses of Neutron Stars

    Directory of Open Access Journals (Sweden)

    Lee Chang-Hwan

    2012-02-01

    Full Text Available Neutron star (NS is one of the most interesting astrophysical compact objects for hardronic physics. It is believed that the central density of NS can reach several times the normal nuclear matter density (ρ0. Hence, the inner part of NS is the ultimate testing place for the physics of dense matter. Recently, the mass of NS in a NS-white dwarf (WD binary PSR J1614-2230 has been estimated to be 1.97 ± 0.04M๏ [1]. Since this estimate is based on the observed Shapiro delay, it can give the lower limit of the maximum NS mass and rules out many soft equations of state. On the other hand, all the well-measured NS masses in NS-NS binaries are smaller than 1.5M๏. In this work, by introducing the supercritical accretion during the binary evolution, we propose a possibility of forming higher mass NS in NS-WD binaries. In this scenario, the lifetimes of NS and WD progenitors are significantly different, and NS in NS-WD binary can accrete > 0.5M๏ after NS formation during the giant phase of the progenitor of WD. On the other hand, for the binary system with NS and heavier (> 8M๏ giants, the first-born NS will accrete more from the companion and can collapse into black hole. The only way to avoid the supercritical accretion is that the initial masses of progenitors of NS binary should be very close so that they evolve almost at the same time and don’t have time to accrete after NS formation.

  4. The maximum mass and radius of neutron stars and the nuclear symmetry energy

    CERN Document Server

    Gandolfi, S; Reddy, Sanjay

    2011-01-01

    We calculate the equation of state of neutron matter with realistic two- and three-nucleon interactions using Quantum Monte Carlo techniques, and demonstrate that the short-range three-neutron interaction determines the correlation between neutron matter energy at nuclear saturation density and the higher densities relevant to neutron stars. Our model for the nuclear interactions makes an experimentally testable prediction for the correlation between the neutron matter energy (which in turn is related to the symmetry energy) and its density dependence. This correlation is solely determined by the strength of the short-range 3 neutron force. The same force also provides a stringent constraint on the maximum mass and radius of neutron stars. An experimental measurement of the symmetry energy with an accuracy of $\\lsim 1$ MeV will enable model predictions for neutron star structure that can be tested with current and anticipated constraints on the masses and radii of neutron stars from x-ray observations.

  5. A two-solar-mass neutron star measured using Shapiro delay

    NARCIS (Netherlands)

    Demorest, P.B.; Pennucci, T.; Ransom, S.M.; Roberts, M.S.E.; Hessels, J.W.T.

    2010-01-01

    Neutron stars are composed of the densest form of matter known to exist in our Universe, the composition and properties of which are still theoretically uncertain. Measurements of the masses or radii of these objects can strongly constrain the neutron star matter equation of state and rule out theor

  6. Mass and Radius of Neutron Stars Constrained by Photospheric Radius Expansion X-ray Bursts

    Science.gov (United States)

    Kwak, Kyujin; Kim, Myungkuk; Kim, Young-Min; Lee, Chang-Hwan

    Simultaneous measurement of mass and radius of a neutron star is important because it provides strong constraint on the equation of state for nuclear matter inside a neutron star. Type I X-ray Bursts (XRBs) that have been observed in low-mass X-ray binaries sometimes show photospheric radius expansion (PRE). By combining observed fluxes, X-ray spectra, and distances of PRE XRBs and using a statistical analysis, it is possible to simultaneously constrain the mass and radius of a neutron star. However, the mass and radius of a neutron star estimated in this method depends on the opacity of accreted material. We investigate the effect of the opacity on the mass and radius estimation by taking into account the cases that the hydrogen mass fraction of accreted material has narrowly-distributed values. We present preliminary results that are investigated with three different values of hydrogen mass fraction and compare our results with previous studies.

  7. Dynamical mass ejection from binary neutron star mergers

    Science.gov (United States)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-08-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ˜60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer time-scales after the mergers, or from core-collapse supernovae.

  8. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    Science.gov (United States)

    Silva, Hector O.; Sotani, Hajime; Berti, Emanuele

    2016-07-01

    The lowest neutron star masses currently measured are in the range 1.0-1.1 M⊙, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass M/M⊙ = 1.174 ± 0.004 (Martinez et al. 2015) in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al. recently found empirical formulas relating the mass and surface redshift of non-rotating neutron stars to the star's central density and to the parameter η ≡ (K0L2)1/3, where K0 is the incompressibility of symmetric nuclear matter and L is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al. to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotational Love number and apsidal constant of slowly rotating neutron stars by integrating the Hartle-Thorne equations at second order in rotation, and we fit all of these quantities as functions of η and of the central density. These fits may be used to constrain η, either via observations of binary pulsars in the electromagnetic spectrum, or via near-future observations of inspiralling compact binaries in the gravitational-wave spectrum.

  9. The evolution of low mass, close binary systems with a neutron star component: a detailed grid

    CERN Document Server

    De Vito, M A

    2012-01-01

    In close binary systems composed of a normal, donor star and an accreting neutron star, the amount of material received by the accreting component is, so far, a real intrigue. In the literature there are available models that link the accretion disk surrounding the neutron star with the amount of material it receives, but there is no model linking the amount of matter lost by the donor star to that falling onto the neutron star. In this paper we explore the evolutionary response of these close binary systems when we vary the amount of material accreted by the neutron star. We consider a parameter \\beta, which represents the fraction of material lost by the normal star that can be accreted by the neutron star. \\beta is considered as constant throughout evolution. We have computed the evolution of a set of models considering initial donor star masses (in solar units) between 0.5 and 3.50, initial orbital periods (in days) between 0.175 and 12, initial masses of neutron stars (in solar units) of 0.80, 1.00, 1.20...

  10. Theoretical and observational constraints on the mass-radius relations of neutron stars

    CERN Document Server

    Boshkayev, Kuantay; Muccino, Marco

    2016-01-01

    We investigate theoretical and observational constraints on the mass-radius relations for neutron stars. For that purpose we consider the model of neutron stars taking into considerations strong, weak, electromagnetic and gravitational interactions in the equation of state and integrate the structure equations within the Hartle-Thorne formalism for rotating configurations. On the basis of the theoretical restrictions imposed by general relativity, mass-shedding and axisymmetric secular instabilities we calculate the upper and lower bounds for the parameters of neutron stars. Our theoretical calculations have been compared and contrasted with the observational constraints and as a result we show that the observational constraints favor stiff equations of state.

  11. Maximal neutron star mass and the resolution of hyperon puzzle in modified gravity

    CERN Document Server

    Astashenok, Artyom V; Odintsov, Sergei D

    2014-01-01

    The so-called hyperon puzzle in the theory of neutron stars is considered in the framework of modified $f(R)$ gravity. We show that for simple hyperon equations of state, it is possible to obtain the maximal neutron star mass which satisfies the recent observational data for PSR J1614-2230, in higher-derivative models with power-law terms as $f(R) = R+\\alpha R^2+ \\beta R^3$. The soft hyperon equation of state under consideration is usually treated as non-realistic in the standard General Relativity. The numerical analysis of Mass-Radius relation for massive neutron stars with hyperon equation of state in modified gravity turns out to be consistent with observations. Thus, we show that the same modified gravity can solve at once three problems: consistent description of the maximal mass of neutron star, realistic Mass-Radius relation and account for hyperons in equation of state.

  12. An Upper Bound on Neutron Star Masses from Models of Short Gamma-ray Bursts

    CERN Document Server

    Lawrence, Scott; Bedaque, Paulo F; Miller, M Coleman

    2015-01-01

    The discovery of two neutron stars with gravitational masses $\\approx 2~M_\\odot$ has placed a strong lower limit on the maximum mass of a slowly rotating neutron star, and with it a strong constraint on the properties of cold matter beyond nuclear density. Current upper mass limits are much looser. Here we note that, if most short gamma-ray bursts are produced by the coalescence of two neutron stars, and if the merger remnant collapses quickly, then the upper mass limit is constrained tightly. We find that if the rotation of the merger remnant is limited only by mass-shedding (which seems plausible based on current numerical studies), then the maximum gravitational mass of a slowly rotating neutron star is between $\\approx 2~M_\\odot$ and $\\approx 2.2~M_\\odot$ if the masses of neutron stars that coalesce to produce gamma-ray bursts are in the range seen in Galactic double neutron star systems. These limits are increased by $\\sim 4$% if the rotation is slowed by $\\sim 30$%, and by $\\sim 15$% if the merger remna...

  13. Gamow's calculation of the neutron star's critical mass revised

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Hendrik; Ruffini, Remo [Sapienza Universita di Roma, Rome (Italy); ICRANet, University of Nice-Sophia Antipolis, Nice Cedex (France)

    2014-09-15

    It has at times been indicated that Landau introduced neutron stars in his classic paper of 1932. This is clearly impossible because the discovery of the neutron by Chadwick was submitted more than one month after Landau's work. Therefore, and according to his calculations, what Landau really did was to study white dwarfs, and the critical mass he obtained clearly matched the value derived by Stoner and later by Chandrasekhar. The birth of the concept of a neutron star is still today unclear. Clearly, in 1934, the work of Baade and Zwicky pointed to neutron stars as originating from supernovae. Oppenheimer in 1939 is also well known to have introduced general relativity (GR) in the study of neutron stars. The aim of this note is to point out that the crucial idea for treating the neutron star has been advanced in Newtonian theory by Gamow. However, this pioneering work was plagued by mistakes. The critical mass he should have obtained was 6.9 M, not the one he declared, namely, 1.5 M. Probably, he was taken to this result by the work of Landau on white dwarfs. We revise Gamow's calculation of the critical mass regarding calculational and conceptual aspects and discuss whether it is justified to consider it the first neutron-star critical mass. We compare Gamow's approach to other early and modern approaches to the problem.

  14. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    CERN Document Server

    Silva, Hector O; Berti, Emanuele

    2016-01-01

    The lowest neutron star masses currently measured are in the range $1.0-1.1~M_\\odot$, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass $M/M_{\\odot} = 1.174 \\pm 0.004$ by Martinez et al [Astrophys.J. 812, 143 (2015)] in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al [PTEP 2014, 051E01 (2014)] recently found empirical formulas relating the mass and surface redshift of nonrotating neutron stars to the star's central density and to the parameter $\\eta\\equiv (K_0 L^2)^{1/3}$, where $K_0$ is the incompressibility of symmetric nuclear matter and $L$ is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotationa...

  15. Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations

    CERN Document Server

    Martinon, Grégoire; Gualtieri, Leonardo; Ferrari, Valeria

    2014-01-01

    Shortly after its birth in a gravitational collapse, a proto-neutron star enters in a phase of quasi-stationary evolution characterized by large gradients of the thermodynamical variables and intense neutrino emission. In few tens of seconds the gradients smooth out while the star contracts and cools down, until it becomes a neutron star. In this paper we study this phase of the proto-neutron star life including rotation, and employing finite temperature equations of state. We model the evolution of the rotation rate, and determine the relevant quantities characterizing the star. Our results show that an isolated neutron star cannot reach, at the end of the evolution, the maximum values of mass and rotation rate allowed by the zero-temperature equation of state. Moreover, a mature neutron star evolved in isolation cannot rotate too rapidly, even if it is born from a proto-neutron star rotating at the mass-shedding limit. We also show that the I-Love-Q relations are violated in the first second of life, but th...

  16. Constraining the neutron star equation of state using quiescent low-mass X-ray binaries

    CERN Document Server

    Jonker, P G

    2007-01-01

    Chandra or XMM-Newton observations of quiescent low-mass X-ray binaries can provide important constraints on the equation of state of neutron stars. The mass and radius of the neutron star can potentially be determined from fitting a neutron star atmosphere model to the observed X-ray spectrum. For a radius measurement it is of critical importance that the distance to the source is well constrained since the fractional uncertainty in the radius is at least as large as the fractional uncertainty in the distance. Uncertainties in modelling the neutron star atmosphere remain. At this stage it is not yet clear if the soft thermal component in the spectra of many quiescent X-ray binaries is variable on timescales too short to be accommodated by the cooling neutron star scenario. This can be tested with a long XMM-Newton observation of the neutron star X-ray transient CenX-4 in quiescence. With such an observation one can use the Reflection Grating Spectrometer spectrum to constrain the interstellar extinction to t...

  17. Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars' rotation

    CERN Document Server

    Dietrich, Tim; Ujevic, Maximiliano; Tichy, Wolfgang

    2016-01-01

    We present new (3+1) dimensional numerical relativity simulations of the binary neutron star (BNS) mergers that take into account the NS spins. We consider different spin configurations, aligned or antialigned to the orbital angular momentum, for equal and unequal mass BNS and for two equations of state. All the simulations employ quasiequilibrium circular initial data in the constant rotational velocity approach, i.e. they are consistent with Einstein equations and in hydrodynamical equilibrium. We study the NS rotation effect on the energetics, the gravitational waves (GWs) and on the possible electromagnetic (EM) emission associated to dynamical mass ejecta. For dimensionless spin magnitudes of $\\chi\\sim0.1$ we find that spin-orbit interactions and also spin-induced-quadrupole deformations affect the late-inspiral-merger dynamics. The latter is, however, dominated by finite-size effects. Spin (tidal) effects contribute to GW phase differences up to 5 (20) radians accumulated during the last eight orbits to...

  18. Theoretical constraints on properties of low-mass neutron stars from EOS of inner crust matters

    CERN Document Server

    Wen, Yongmei

    2016-01-01

    By employing four typical equation of states (EOSs) of the inner crust matters, the constraint on properties of low-mass neutron stars are theoretically investigated. Based on the well known fact that there is a big gap between the neutron stars and white dwarfs in the mass-radius sequence of compact stars, here we explicitly point out the forbidden region for the central density and stellar radius to form a compact stars, that is, there is no compact star in the nature having central density in the region from about $10^{12}~kg/m^3$ to $10^{17}~kg/m^3$, and there is also no compact star having a radius in the region from about 400 km to 2000 km. It is found that for a low-mass neutron star with central densities at subnuclear densities, the stellar mass is mainly determined by the softness of the EOS at the higher density region ($ > 10^{16}~\\textrm{kg.m}^{-3}$) while the stellar radius is dependent on the softness of the EOS at lower density region ($ < 10^{16}~\\textrm{kg.m}^{-3}$). For a stable neutron ...

  19. The Equation of State from Observed Masses and Radii of Neutron Stars

    CERN Document Server

    Steiner, Andrew W; Brown, Edward F

    2010-01-01

    We determine an empirical dense matter equation of state (EOS) from a heterogeneous set of seven neutron stars with well-determined distances. Our dataset consists of the three type I X-ray bursters with photospheric radius expansion studied by Ozel et al., along with thermal emission from three transient low-mass X-ray binaries and the isolated cooling neutron star, RX J1856-3754. We critically assess the mass and radius determinations from the X-ray bursts and show explicitly how the systematic uncertainties, such as the radius of the photosphere at touchdown, affect the best-fit masses and radii. As a result of including these uncertainties, our mass and radius constraints are weaker than previously found. Nevertheless, when combined with radius constraints from neutron star transients and the isolated neutron star RX J1856-3754, we do find significant constraints on the mass-radius relation for neutron stars, and hence on the pressure-density relation of dense matter. We introduce a parameterized EOS and ...

  20. Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the mass ratio

    Science.gov (United States)

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

    2017-01-01

    We present new (3 +1 )D numerical relativity simulations of the binary neutron star (BNS) merger and postmerger phase. We focus on a previously inaccessible region of the binary parameter space spanning the binary's mass ratio q ˜1.00 - 1.75 for different total masses and equations of state, and up to q ˜2 for a stiff BNS system. We study the mass ratio effect on the gravitational waves (GWs) and on the possible electromagnetic (EM) emission associated with dynamical mass ejecta. We compute waveforms, spectra, and spectrograms of the GW strain including all the multipoles up to l =4 . The mass ratio has a specific imprint on the GW multipoles in the late-inspiral-merger signal, and it affects qualitatively the spectra of the merger remnant. The multipole effect is also studied by considering the dependency of the GW spectrograms on the source's sky location. Unequal mass BNSs produce more ejecta than equal mass systems with ejecta masses and kinetic energies depending almost linearly on q . We estimate luminosity peaks and light curves of macronova events associated with the mergers using a simple approach. For q ˜2 the luminosity peak is delayed for several days and can be up to 4 times larger than for the q =1 cases. The macronova emission associated with the q ˜2 BNS is more persistent in time and could be observed for weeks instead of a few days (q =1 ) in the near infrared. Finally, we estimate the flux of possible radio flares produced by the interaction of relativistic outflows with the surrounding medium. Also in this case a large q can significantly enhance the emission and delay the peak luminosity. Overall, our results indicate that the BNS merger with a large mass ratio has EM signatures distinct from the equal mass case and more similar to black hole-neutron star binaries.

  1. Neutron star mass-radius relation with gravitational field shielding by a scalar field

    Institute of Scientific and Technical Information of China (English)

    Bo-Jun Zhang; Tian-Xi Zhang; Padmaja Guggilla; Mostafa Dokhanian

    2013-01-01

    The currently well-developed models for equations of state (EoSs) have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass.To explain these measurements,the theory of gravitational field shielding by a scalar field is applied.This theory was recently developed in accordance with the five-dimensional (5D) fully covariant Kaluza-Klein (KK) theory that has successfully unified Einstein's general relativity and Maxwell's electromagnetic theory.It is shown that a massive,compact neutron star can generate a strong scalar field,which can significantly shield or reduce its gravitational field,thus making it more massive and more compact.The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars.In addition,the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars (e.g.,40 M⊙ as measured recently) actually formed neutron stars rather than black holes as expected.The EoS models,ruled out by measurements of small radius and/or large mass neutron stars according to the theory of general relativity,can still work well in terms of the 5D fully covariant KK theory with a scalar field.

  2. Accuracy in measuring the neutron star mass in the gravitational wave parameter estimation for black hole-neutron star binaries

    Science.gov (United States)

    Cho, Hee-Suk

    2016-09-01

    Recently, two gravitational wave (GW) signals, named as GW150914 and GW151226, have been detected by the two LIGO detectors. Although both signals were identified as originating from merging black hole (BH) binaries, GWs from systems containing neutron stars (NSs) are also expected to be detected in the near future by the advanced detector network. In this work, we assess the accuracy in measuring the NS mass ( M NS) for the GWs from BH-NS binaries adopting the Advanced LIGO sensitivity with a signal-to-noise ratio of 10. By using the Fisher matrix method, we calculate the measurement errors ( σ) in M NS assuming a NS mass of 1 ≤ M NS/ M ⊙ ≤ 2 and low-mass BHs with masses in the range of 4 ≤ M BH/ M ⊙ ≤ 10. We use the TaylorF2 waveform model in which the spins are aligned with the orbital angular momentum, but here we only consider the BH spins. We find that the fractional errors ( σ/ M NS × 100) are in the range of 10% - 50% in our mass region for a given dimensionless BH spin χBH = 0. The errors tend to increase as the BH spin increases, and this tendency is stronger for higher NS masses (or higher total masses). In particular, for the highest mass NSs ( M NS = 2 M ⊙), the errors σ can be larger than the true value of M NS if the dimensionless BH spin exceeds ~ 0.6.

  3. The millisecond pulsar mass distribution: Evidence for bimodality and constraints on the maximum neutron star mass

    CERN Document Server

    Antoniadis, John; Ozel, Feryal; Barr, Ewan; Champion, David J; Freire, Paulo C C

    2016-01-01

    The mass function of neutron stars (NSs) contains information about the late evolution of massive stars, the supernova explosion mechanism, and the equation-of-state of cold, nuclear matter beyond the nuclear saturation density. A number of recent NS mass measurements in binary millisecond pulsar (MSP) systems increase the fraction of massive NSs (with $M > 1.8$ M$_{\\odot}$) to $\\sim 20\\% $ of the observed population. In light of these results, we employ a Bayesian framework to revisit the MSP mass distribution. We find that a single Gaussian model does not sufficiently describe the observed population. We test alternative empirical models and infer that the MSP mass distribution is strongly asymmetric. The diversity in spin and orbital properties of high-mass NSs suggests that this is most likely not a result of the recycling process, but rather reflects differences in the NS birth masses. The asymmetry is best accounted for by a bimodal distribution with a low mass component centred at $1.393_{-0.029}^{+0.0...

  4. Neutron Stars Recent Developments

    CERN Document Server

    Heiselberg, H

    1999-01-01

    Recent developments in neutron star theory and observation are discussed. Based on modern nucleon-nucleon potentials more reliable equations of state for dense nuclear matter have been constructed. Furthermore, phase transitions such as pion, kaon and hyperon condensation, superfluidity and quark matter can occur in cores of neutron stars. Specifically, the nuclear to quark matter phase transition and its mixed phases with intriguing structures is treated. Rotating neutron stars with and without phase transitions are discussed and compared to observed masses, radii and glitches. The observations of possible heavy $\\sim 2M_\\odot$ neutron stars in X-ray binaries and QPO's require relatively stiff equation of states and restrict strong phase transitions to occur at very high nuclear densities only.

  5. Effect of the equation of state on the maximum mass of differentially rotating neutron stars

    Science.gov (United States)

    Studzińska, A. M.; Kucaba, M.; Gondek-Rosińska, D.; Villain, L.; Ansorg, M.

    2016-12-01

    Knowing the value of the maximum mass of a differentially rotating relativistic star is a key step towards the understanding of the signals to be expected from the merger of binary neutron stars, one of the most awaited alternative sources of gravitational waves after binary black holes. In this paper, we study the effects of differential rotation and of the equation of state on the maximum mass of rotating neutron stars modelled as relativistic polytropes with various adiabatic indices. Calculations are performed using a highly accurate numerical code, based on a multidomain spectral method. We thoroughly explore the parameter space and determine how the maximum mass depends on the stiffness, on the degree of differential rotation and on the maximal density, taking into account all the types of solutions that were proven to exist in a preceding paper. The highest increase with respect to the maximum mass for non-rotating stars with the same equation of state is reached for a moderate stiffness. With differential rotation, the maximum mass can even be 3-4 times higher than it is for static stars. This result may have important consequences for the gravitational wave signal from coalescing neutron star binaries or for some supernovae events.

  6. Uniformly rotating neutron stars

    CERN Document Server

    Boshkayev, Kuantay

    2016-01-01

    In this chapter we review the recent results on the equilibrium configurations of static and uniformly rotating neutron stars within the Hartle formalism. We start from the Einstein-Maxwell-Thomas-Fermi equations formulated and extended by Belvedere et al. (2012, 2014). We demonstrate how to conduct numerical integration of these equations for different central densities ${\\it \\rho}_c$ and angular velocities $\\Omega$ and compute the static $M^{stat}$ and rotating $M^{rot}$ masses, polar $R_p$ and equatorial $R_{\\rm eq}$ radii, eccentricity $\\epsilon$, moment of inertia $I$, angular momentum $J$, as well as the quadrupole moment $Q$ of the rotating configurations. In order to fulfill the stability criteria of rotating neutron stars we take into considerations the Keplerian mass-shedding limit and the axisymmetric secular instability. Furthermore, we construct the novel mass-radius relations, calculate the maximum mass and minimum rotation periods (maximum frequencies) of neutron stars. Eventually, we compare a...

  7. Accuracy in Measuring the Neutron Star Mass in Gravitational Wave Parameter Estimation for Black Hole-Neutron Star Binaries

    CERN Document Server

    Cho, Hee-Suk

    2016-01-01

    Recently, two gravitational wave (GW) signals, named as GW150914 and GW151226, have been detected by the two LIGO detectors. Although both signals were identified as originating from merging black hole (BH) binaries, GWs from systems containing neutron stars (NSs) are also expected to be detected in the near future by the Advanced detector network. In this work, we assess the accuracy in measuring the NS mass ($M_{ns}$) for the GWs from BH-NS binaries adopting the Advanced LIGO sensitivity with a signal-to-noise ratio of 10. By using the Fisher matrix method, we calculate the measurement errors ($\\sigma$) in $M_{ns}$ assuming the NS mass of $1 \\leq M_{ns}/M_{\\odot} \\leq 2$ and low mass BHs with the range of $4 \\leq M_{bh}/M_{\\odot} \\leq 10$. We used the TaylorF2 waveform model where the spins are aligned with the orbital angular momentum, but here we only consider the BH spins. We find that the fractional errors ($\\sigma/M_{ns} \\times 100$) are in the range of $10\\% - 50\\%$ in our mass region for a given dime...

  8. The Neutron Star Mass-Radius Relation and the Equation of State of Dense Matter

    CERN Document Server

    Steiner, Andrew W; Brown, Edward F

    2012-01-01

    The equation of state (EOS) of dense matter has been a long-sought goal of nuclear physics. Equations of state generate unique mass versus radius (M-R) relations for neutron stars, the ultra-dense remnants of stellar evolution. In this work, we determine the neutron star mass-radius relation and, based on recent observations of both transiently accreting and bursting sources, we show that the radius of a 1.4 solar mass neutron star lies between 10.4 and 12.9 km, independent of assumptions about the composition of the core. We show, for the first time, that these constraints remain valid upon removal from our sample of the most extreme transient sources or of the entire set of bursting sources; our constraints also apply even if deconfined quark matter exists in the neutron star core. Our results significantly constrain the dense matter EOS and are, furthermore, consistent with constraints from both heavy-ion collisions and theoretical studies of neutron matter. We predict a relatively weak dependence of the s...

  9. Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the mass-ratio

    CERN Document Server

    Dietrich, Tim; Tichy, Wolfgang; Bernuzzi, Sebastiano; Bruegmann, Bernd

    2016-01-01

    We present new (3+1)D numerical relativity simulations of the binary neutron star (BNS) merger and postmerger phase. We focus on a previously inaccessible region of the binary parameter space spanning the binary's mass-ratio $q\\sim1.00-1.75$ for different total masses and equations of state, and up to $q\\sim2$ for a stiff BNS system. We study the mass-ratio effect on the gravitational waves (GWs) and on the possible electromagnetic emission associated to dynamical mass ejecta. We compute waveforms, spectra, and spectrograms of the GW strain including all the multipoles up to $l=4$. The mass-ratio has a specific imprint on the GW multipoles in the late-inspiral-merger signal, and it affects qualitatively the spectra of the merger remnant. The multipole effect is also studied by considering the dependency of the GW spectrograms on the source's sky location. Unequal mass BNSs produce more ejecta than equal mass systems with ejecta masses and kinetic energies depending almost linearly on $q$. We estimate luminosi...

  10. Nuclear Mass Predictions for the Crustal Composition of Neutron Stars: A Bayesian Neural Network Approach

    CERN Document Server

    Utama, R; Prosper, H B

    2016-01-01

    Besides their intrinsic nuclear-structure value, nuclear mass models are essential for astrophysical applications, such as r-process nucleosynthesis and neutron-star structure. To overcome the intrinsic limitations of existing "state-of-the-art" mass models, we propose a refinement based on a Bayesian Neural Network (BNN) formalism. A novel BNN approach is implemented with the goal of optimizing mass residuals between theory and experiment. A significant improvement (of about 40%) in the mass predictions of existing models is obtained after BNN refinement. Moreover, these improved results are now accompanied by proper statistical errors. Finally, by constructing a "world average" of these predictions, a mass model is obtained that is used to predict the composition of the outer crust of a neutron star. The power of the Bayesian neural network method has been successfully demonstrated by a systematic improvement in the accuracy of the predictions of nuclear masses. Extension to other nuclear observables is a n...

  11. Time-of-flight mass measurements for nuclear processes in neutron star crusts

    Energy Technology Data Exchange (ETDEWEB)

    Estrade, Alfredo [National Superconducting Cyclotron Laboratory (NSCL); Matos, M. [Louisiana State University; Schatz, Hendrik [Michigan State University, East Lansing; Amthor, A. M. [National Superconducting Cyclotron Laboratory (NSCL); Bazin, D. [National Superconducting Cyclotron Laboratory (NSCL); Beard, Mary [University of Notre Dame, IN; Becerril, A. [National Superconducting Cyclotron Laboratory (NSCL); Brown, Edward [Michigan State University, East Lansing; Elliot, T [National Superconducting Cyclotron Laboratory (NSCL); Gade, A. [National Superconducting Cyclotron Laboratory (NSCL); Galaviz, D. [National Superconducting Cyclotron Laboratory (NSCL); George, S. [National Superconducting Cyclotron Laboratory (NSCL); Gupta, Sanjib [Indian Institute of Technology, Kanpur; Hix, William Raphael [ORNL; Lau, Rita [National Superconducting Cyclotron Laboratory (NSCL); Moeller, Peter [Los Alamos National Laboratory (LANL); Pereira, J. [National Superconducting Cyclotron Laboratory (NSCL); Portillo, M. [National Superconducting Cyclotron Laboratory (NSCL); Rogers, A. M. [National Superconducting Cyclotron Laboratory (NSCL); Shapira, Dan [ORNL; Smith, E. [Ohio State University; Stolz, A. [Michigan State University, East Lansing; Wallace, M. [Los Alamos National Laboratory (LANL); Wiescher, Michael [University of Notre Dame, IN

    2011-01-01

    The location of electron capture heat sources in the crust of accreting neutron stars depends on the masses of extremely neutron-rich nuclei. We present first results from a new implementation of the time-of-flight technique to measure nuclear masses of rare isotopes at the National Supercon- ducting Cyclotron Laboratory. The masses of 16 neutron-rich nuclei in the Sc Ni element range were determined simultaneously, improving the accuracy compared to previous data in 12 cases. The masses of 61V, 63Cr, 66Mn, and 74Ni were measured for the first time with mass excesses of 30.510(890) MeV, 35.280(650) MeV, 36.900(790) MeV, and 49.210(990) MeV, respectively. With the measurement of the 66Mn mass, the location of the two dominant heat sources in the outer crust of accreting neutron stars, which exhibit so called superbursts, is now experimentally constrained. We find that the location of the 66Fe 66Mn electron capture transition occurs sig- nificantly closer to the surface than previously assumed because our new experimental Q-value is 2.1 MeV smaller than predicted by the FRDM mass model. The results also provide new insights into the structure of neutron-rich nuclei around N = 40.

  12. Masses of Neutron Stars in High-Mass X-ray Binaries with Optical Astrometry

    CERN Document Server

    Tomsick, John A

    2010-01-01

    Determining the type of matter that is inside a neutron star (NS) has been a long-standing goal of astrophysics. Despite this, most of the NS equations of state (EOS) that predict maximum masses in the range 1.4-2.8 solar masses are still viable. Most of the precise NS mass measurements that have been made to date show values close to 1.4 solar masses, but a reliable measurement of an over-massive NS would constrain the EOS possibilities. Here, we investigate how optical astrometry at the microarcsecond level can be used to map out the orbits of High-Mass X-ray Binaries (HMXBs), leading to tight constraints on NS masses. While previous studies by Unwin and co-workers and Tomsick and co-workers discuss the fact that the future Space Interferometry Mission should be capable of making such measurements, the current work describes detailed simulations for 6 HMXB systems, including predicted constraints on all orbital parameters. We find that the direct NS masses can be measured to an accuracy of 2.5% (1-sigma) in...

  13. Neutron Star masses from the Field Correlator Method Equation of State

    Directory of Open Access Journals (Sweden)

    Zappalà D.

    2014-04-01

    Full Text Available We analyse the hadron-quark phase transition in neutron stars by confronting the hadronic Equation of State (EoS obtained according to the microscopic Brueckner-Hartree-Fock many body theory, with the quark matter EoS derived within the Field Correlator Method. In particular, the latter EoS is only parametrized in terms of the gluon condensate and the large distance quark-antiquark potential, so that the comparison of the results of this analysis with the most recent measurements of heavy neutron star masses provides some physical constraints on these two parameters.

  14. Prospects for Measuring Neutron-Star Masses and Radii with X-Ray Pulse Profile Modeling

    CERN Document Server

    Psaltis, Dimitrios; Chakrabarty, Deepto

    2013-01-01

    Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, rotating neutron stars provides a direct method for measuring neutron-star properties. This technique constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this paper, we determine the number of distinct observables that can be derived from pulse profile modeling and show that using only bolometric pulse profiles is insufficient for breaking the degeneracy between inferred neutron-star radius and mass. However, we also show that for moderately spinning (300-800 Hz) neutron stars, analysis of pulse profiles in two different energy bands provides additional constraints that allow a unique determination of the neutron-star properties. Using the fractional amplitudes of the fundamental and the first harmonic of the pulse profile in addition to the amplitude and phase difference of the spectral color oscillations, we quantify the signal-to-noise ratio necessary to achieve a speci...

  15. Maximum mass of a hot neutron star with a quark core

    Institute of Scientific and Technical Information of China (English)

    Tayebeh Yazdizadeh; Gholam Hossein Bordbar

    2011-01-01

    We have considered a hot neutron star with a quark core, a mixed phase of quark-hadron matter, and a hadronic matter crust and have determined the equation of state of the hadronic phase and the quark phase. We have then found the equation of state of the mixed phase under the Gibbs conditions. Finally, we have computed the structure of a hot neutron star with a quark core and compared our results with those of the neutron star without a quark core. For the quark matter calculations, we have used the MIT bag model in which the total energy of the system is considered as the kinetic energy of the particles plus a bag constant. For the hadronic matter calculations, we have used the lowest order constrained variational formalism. Our calculations show that the results for the maximum gravitational mass of a hot neutron star with a quark core are substantially different from those of a neutron star without the quark core.

  16. Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

    Science.gov (United States)

    Meszaros, P.; Rees, M. J.

    1992-01-01

    A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

  17. Inner crust of neutron stars with mass-fitted Skyrme interaction

    CERN Document Server

    Madhuri, K; Routray, T R; Pattnaik, S P

    2016-01-01

    The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using $\\beta$-equilibrated nuclear matter obtained from Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set is able to describe highly massive compact stars $\\sim$2$M_{\\odot}$. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar:$R\\geq$ 3.69+3.44 M/$M_{\\odot}$. ...

  18. Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

    Science.gov (United States)

    Meszaros, P.; Rees, M. J.

    1992-01-01

    A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

  19. Cooling of Neutron Stars

    Directory of Open Access Journals (Sweden)

    Grigorian H.

    2010-10-01

    Full Text Available We introduce the theoretical basis for modeling the cooling evolution of compact stars starting from Boltzmann equations in curved space-time. We open a discussion on observational verification of different neutron star models by consistent statistics. Particular interest has the question of existence of quark matter deep inside of compact object, which has to have a specific influence on the cooling history of the star. Besides of consideration of several constraints and features of cooling evolution, which are susceptible of being critical for internal structure of hot compact stars we have introduced a method of extraction of the mass distribution of the neutron stars from temperature and age data. The resulting mass distribution has been compared with the one suggested by supernove simulations. This method can be considered as an additional checking tool for the consistency of theoretical modeling of neutron stars. We conclude that the cooling data allowed existence of neutron stars with quark cores even with one-flavor quark matter.

  20. The Nuclear Symmetry Energy and the Mass-Radius Relation of Neutron Stars

    Science.gov (United States)

    Lattimer, James

    2017-01-01

    The assumptions that i) neutron stars have hadronic crusts, ii) the equation of state is causal, iii) GR is the correct theory of gravity, and iv) their largest observed mass is 2 solar masses, when coupled with recent results from nuclear experiment and theoretical studies of neutron matter, generate powerful constraints on their structure. These include restriction of the radii of typical neutron stars to the range 11-13 km, as well as significant correlations among their masses, compactnesses, moments of inertia, binding energies, and tidal deformabilities. In addition, properties of quark matter, including the location and magnitude of the quark-hadron phase transition, can also be limited. The implications of recent and forthcoming experiments, such as those pertaining to the neutron skin thickness and astrophysical measurements of various structural properties is discussed. For the latter, emphasis is placed on pulsar timing, X-ray observations, supernova neutrino detections, and gravitational waves from mergers involving neutron stars. Supported in part by the US DOE grant DE-AC02-87ER40317.

  1. A New View on the Maximum Mass of Differentially Rotating Neutron Stars

    Science.gov (United States)

    Gondek-Rosińska, D.; Kowalska, I.; Villain, L.; Ansorg, M.; Kucaba, M.

    2017-03-01

    We study the main astrophysical properties of differentially rotating neutron stars described as stationary and axisymmetric configurations of a moderately stiff {{Γ }}=2 polytropic fluid. The high level of accuracy and of stability of our relativistic multidomain pseudo-spectral code enables us to explore the whole solution space for broad ranges of the degree of differential rotation, but also of the stellar density and oblateness. Staying within an astrophysically motivated range of rotation profiles, we investigate the characteristics of neutron stars with maximal mass for all types of families of differentially rotating relativistic objects identified in a previous article. We find that the maximum mass depends on both the degree of differential rotation and the type of solution. It turns out that the maximum allowed mass can be up to 4 times higher than what it is for nonrotating stars with the same equation of state. Such values are obtained for a modest degree of differential rotation but for one of the newly discovered types of solutions. Since such configurations of stars are not that extreme, this result may have important consequences for the gravitational wave signal expected from coalescing neutron star binaries or from some supernova events.

  2. Role of the electron mass in damping chiral plasma instability in Supernovae and neutron stars

    Science.gov (United States)

    Grabowska, Dorota; Kaplan, David B.; Reddy, Sanjay

    2015-04-01

    We show that the nonzero electron mass plays a critical role in determining the magnetic properties of neutron stars by suppressing the generation of the chiral charge density needed to trigger a strong chiral plasma instability during the core collapse of supernovae. This instability has been proposed as a plausible mechanism for generating extremely large helical magnetic fields in neutron stars at their birth; the mechanism relies on the generation of a large nonequilibrium chiral charge density via electron capture reactions that selectively deplete left-handed electrons during core collapse and the early evolution of the protoneutron star. Our calculation shows that the electron chirality violation rate induced by Rutherford scattering, despite being suppressed by the smallness of the electron mass relative to the electron chemical potential, is still fast compared to the weak interaction electron capture rate. The resulting asymmetry between right- and left-handed electron densities is therefore unlikely to attain an astrophysically relevant magnitude.

  3. Mass measurements of neutron rich isotopes in the Fe region and electron capture processes in neutron star crusts

    Energy Technology Data Exchange (ETDEWEB)

    Estrade, Alfredo [National Superconducting Cyclotron Laboratory (NSCL); Matos, M. [Louisiana State University; Schatz, Hendrik [Michigan State University, East Lansing; Amthor, A. M. [National Superconducting Cyclotron Laboratory (NSCL); Beard, Mary [University of Notre Dame, IN; Brown, Edward [Michigan State University, East Lansing; Bazin, D. [National Superconducting Cyclotron Laboratory (NSCL); Becerril, A. [National Superconducting Cyclotron Laboratory (NSCL); Elliot, T [National Superconducting Cyclotron Laboratory (NSCL); Gade, A. [National Superconducting Cyclotron Laboratory (NSCL); Galaviz, D. [National Superconducting Cyclotron Laboratory (NSCL); Gupta, Sanjib [Indian Institute of Technology, Kanpur; Hix, William Raphael [ORNL; Lau, Rita [National Superconducting Cyclotron Laboratory (NSCL); Moeller, Peter [Los Alamos National Laboratory (LANL); Pereira, J. [National Superconducting Cyclotron Laboratory (NSCL); Portillo, M. [National Superconducting Cyclotron Laboratory (NSCL); Rogers, A. M. [National Superconducting Cyclotron Laboratory (NSCL); Shapira, Dan [ORNL; Smith, E. [Ohio State University; Stolz, A. [Michigan State University, East Lansing; Wallace, M. [Los Alamos National Laboratory (LANL); Wiescher, Michael [University of Notre Dame, IN

    2010-01-01

    Experimental knowledge of nuclear masses of exotic nuclei is important for understanding nu- clear structure far from the valley of -stability, and as a direct input into astrophysical models. Electron capture processes in the crust of accreting neutron stars have been proposed as a heat source that can affect the thermal structure of the star. Nuclear masses of very neutron-rich nu- clides are necessary inputs to model the electron capture process. The time-of-flight (TOF) mass measurement technique allows measurements on very short-lived nuclei. It has been effectively applied using the fast fragment beams produced at the National Superconducting Cyclotron Lab (NSCL) to reach masses very far from stability. Measurements were performed for neutron-rich isotopes in the region of the N=32 and N=40 subshells, which coincides with the mass range of carbon superburst ashes. We discuss reaction network calculations performed to investigate the impact of our new measurements and to compare the effect of using different global mass models in the calculations. It is observed that the process is sensitive to the differences in the odd-even mass staggering predicted by the mass models, and our new result for 66Mn has a significant impact on the distribution of heat sources in the crust.

  4. Time-of-Flight Mass Measurements for Nuclear Processes in Neutron Star Crusts

    Science.gov (United States)

    Estradé, A.; Matoš, M.; Schatz, H.; Amthor, A. M.; Bazin, D.; Beard, M.; Becerril, A.; Brown, E. F.; Cyburt, R.; Elliot, T.; Gade, A.; Galaviz, D.; George, S.; Gupta, S. S.; Hix, W. R.; Lau, R.; Lorusso, G.; Möller, P.; Pereira, J.; Portillo, M.; Rogers, A. M.; Shapira, D.; Smith, E.; Stolz, A.; Wallace, M.; Wiescher, M.

    2011-10-01

    We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of V61, Cr63, Mn66, and Ni74 measured for the first time with mass excesses of -30.510(890)MeV, -35.280(650)MeV, -36.900(790)MeV, and -49.210(990)MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the Fe66→Mn66 electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.

  5. A toroidal vortex field as an origin of the narrow mass spectrum of neutron stars

    Science.gov (United States)

    Kontorovich, V. M.

    2016-03-01

    The evolution and collapse of a gaseous, self-gravitating sphere in the presence of an internal massive toroidal vortex analogous to the vortex created by the toroidal magnetic field of the Sun is considered. When thermal pressure is taken into account, for sufficiently high masses, the instability is preserved even for a polytropic index γ neutrons differs appreciably. In the ultrarelativistic limit, an interval of stablemasses arises in a neutron gas, between a minimum mass that depends on the circulation velocity in the vortex and the critical mass for the formation of a black hole. This suggests toroidal vortex fields as a possible physical origin for the observed narrow spectrum of neutron-star masses.

  6. Equation of state of dense matter and the minimum mass of cold neutron stars

    CERN Document Server

    Haensel, P; Douchin, F

    2002-01-01

    Equilibrium configurations of cold neutron stars near the minimum mass are studied, using the recent equation of state SLy, which describes in a unified, physically consistent manner, both the solid crust and the liquid core of neutron stars. Results are compared with those obtained using an older FPS equation of state of cold catalyzed matter. The value of M_min\\simeq 0.09M_sun depends very weakly on the equation of state of cold catalyzed matter: it is 0.094 M_sun for the SLy model, and 0.088 M_sun for the FPS one. Central density at M_min is significantly lower than the normal nuclear density: for the SLy equation of state we get central density 1.7 10^{14} g/cm^3, to be compared with 2.3 10^{14} g/cm^3 obtained for the FPS one. Even at M_min, neutron stars have a small liquid core of radius of about 4 km, containing some 2-3% of the stellar mass. Neutron stars with 0.09 M_sun

  7. Time-of-flight mass measurements for nuclear processes in neutron star crusts

    CERN Document Server

    Estrade, A; Schatz, H; Amthor, A M; Bazin, D; Beard, M; Becerril, A; Brown, E F; Cyburt, R; Elliot, T; Gade, A; Galaviz, D; George, S; Gupta, S S; Hix, W R; Lau, R; Lorusso, G; Moller, P; Pereira, J; Portillo, M; Rogers, A M; Shapira, D; Smith, E; Stolz, A; Wallace, M; Wiescher, M

    2011-01-01

    The location of electron capture heat sources in the crust of accreting neutron stars depends on the masses of extremely neutron-rich nuclei. We present first results from a new implementation of the time-of-flight technique to measure nuclear masses of rare isotopes at the National Superconducting Cyclotron Laboratory. The masses of 16 neutron-rich nuclei in the scandium -- nickel range were determined simultaneously, improving the accuracy compared to previous data in 12 cases. The masses of $^{61}${V}, $^{63}${Cr}, $^{66}${Mn}, and $^{74}${Ni} were measured for the first time with mass excesses of $-30.510(890)$ MeV, $-35.280(650)$ MeV, $-36.900(790)$ MeV, and $-49.210(990)$ MeV, respectively. With the measurement of the $^{66}$Mn mass, the locations of the two dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit superbursts are now experimentally constrained. We find that the location of the $^{66}$Fe$\\rightarrow^{66}$Mn electron capture transition occurs signi...

  8. Oscillations of red dwarfs in evolved low-mass binaries with neutron stars

    Science.gov (United States)

    Sarna, Marek J.; Lee, Umin; Muslimov, Alexander G.

    1994-01-01

    We investigate a novel aspect of a problem related to the properties of low-mass binaries (LMBs) with millisecond pulsars: the pulsations of the red dwarf (donor) companion of the neutron star (NS). The illumination of the donor star by the pulsar's high-energy nonthermal radiation and relativistic wind may substantially affect its structure. We present a quantitative analysis of the oscillation spectrum of a red dwarf which has evolved in an LMB and has undergone the stage of evaporation. We calculate the p- and g-modes for red dwarfs with masses in the interval (0.2-0.6) stellar mass. For comparison, similar calculations are presented for zero age main-sequence (ZAMS) stars of the same masses. For less massive donor stars (approximately 0.2 stellar mass) the oscillation spectrum becomes quantitatively different from that of their ZAMS counterparts. The differnce is due to the fact that a ZAMS star of 0.2 stellar mass is fully convective, while the donor star in an LMB is expected to be far from thermal equilibrium and not fully convective. As a result, in contrast to a low-mass ZAMS star, a red dwarf of the same mass in an LMB allows the existence of g-modes. We also consider tidally forced g-modes, and perform a linear analysis of these oscillations for different degrees of nonsynchronism between the orbital and spin rotation of the red dwarf component. We demonstrate the existence of a series of reasonances for the low-order g-modes which may occur in LMBs at a late stage of their evolution. We discuss the possibility that these oscillations may trigger Roche lobe overflow and sudden mass loss by the donor star. Further implications of this effect for gamma- and X-ray burst phenomena are outlined.

  9. The lowest-mass stellar black holes: catastrophic death of neutron stars in gamma-ray bursts

    CERN Document Server

    Belczynski, K; Kalogera, V; Rasio, F; Taam, R; Bulik, T

    2007-01-01

    Mergers of double neutron stars are considered the most likely progenitors for short gamma-ray bursts. Indeed such a merger can produce a black hole with a transient accreting torus of nuclear matter and the conversion of the torus mass-energy to radiation can power a gamma-ray burst. Using available binary pulsar observations supported by our extensive evolutionary calculations of double neutron star formation, we demonstrate that the fraction of mergers that can form a black hole -- torus system depends very sensitively on the (largely unknown) maximum neutron star mass. We show that the available observations and models put a very stringent constraint on this maximum mass under the assumption that a majority of short gamma-ray bursts originate in double neutron star mergers. Specifically, we find that the maximum neutron star mass must be within 2--2.5 Msun. Moreover, a single unambiguous measurement of a neutron star mass above 2.5 Msun would exclude double neutron star mergers as short gamma-ray burst pr...

  10. Mass, radius and composition of the outer crust of nonaccreting cold neutron stars

    Science.gov (United States)

    Hempel, Matthias; Schaffner-Bielich, Jürgen

    2008-01-01

    The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick and Sutherland, which was extended by including higher order corrections of the atomic binding, screening, exchange and zero-point energy. The most recent experimental nuclear data from the atomic mass table of Audi, Wapstra and Thibault from 2003 are used. Extrapolation to the drip line is utilized by various state-of-the-art theoretical nuclear models (finite range droplet, relativistic nuclear field and non-relativistic Skyrme Hartree Fock parameterizations). The different nuclear models are compared with respect to the mass and radius of the outer crust for different neutron star configurations and the nuclear compositions of the outer crust.

  11. Mass, radius, and composition of the outer crust of nonaccreting cold neutron stars

    CERN Document Server

    Hempel, Matthias

    2008-01-01

    The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick, and Sutherland, which was extended by including higher order corrections of the atomic binding, screening, exchange and zero-point energy. The most recent experimental nuclear data from the atomic mass table of Audi, Wapstra, and Thibault from 2003 is used. Extrapolation to the drip line is utilized by various state-of-the-art theoretical nuclear models (finite range droplet, relativistic nuclear field and non-relativistic Skyrme Hartree-Fock parameterizations). The different nuclear models are compared with respect to the mass and radius of the outer crust for different neutron star configurations and the nuclear compositions of the outer crust.

  12. Accreting Neutron Stars in Low-Mass X-Ray Binary Systems

    CERN Document Server

    Lamb, Frederick K

    2007-01-01

    Using the Rossi X-ray Timing Explorer (RossiXTE), astronomers have discovered that disk-accreting neutron stars with weak magnetic fields produce three distinct types of high-frequency X-ray oscillations. These oscillations are powered by release of the binding energy of matter falling into the strong gravitational field of the star or by the sudden nuclear burning of matter that has accumulated in the outermost layers of the star. The frequencies of the oscillations reflect the orbital frequencies of gas deep in the gravitational field of the star and/or the spin frequency of the star. These oscillations can therefore be used to explore fundamental physics, such as strong-field gravity and the properties of matter under extreme conditions, and important astrophysical questions, such as the formation and evolution of millisecond pulsars. Observations using RossiXTE have shown that some two dozen neutron stars in low-mass X-ray binary systems have the spin rates and magnetic fields required to become milliseco...

  13. Reassessing The Fundamentals New Constraints on the Evolution, Ages and Masses of Neutron Stars

    Science.gov (United States)

    Kızıltan, Bülent

    2011-09-01

    The ages and masses of neutron stars (NSs) are two fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these two derived parameters play an important role in understanding of advanced stages of stellar evolution and the physics that govern relevant processes. Here I summarize new constraints on the ages and masses of NSs with an evolutionary perspective. I show that the observed P-Ṗ demographics is more diverse than what is theoretically predicted for the standard evolutionary channel. In particular, standard recycling followed by dipole spin-down fails to reproduce the population of millisecond pulsars with higher magnetic fields (B > 4 × 108 G) at rates deduced from observations. A proper inclusion of constraints arising from binary evolution and mass accretion offers a more realistic insight into the age distribution. By analytically implementing these constraints, I propose a ``modified'' spin-down age (τ~) for millisecond pulsars that gives estimates closer to the true age. Finally, I independently analyze the peak, skewness and cutoff values of the underlying mass distribution from a comprehensive list of radio pulsars for which secure mass measurements are available. The inferred mass distribution shows clear peaks at 1.35 Msolar and 1.50 Msolar for NSs in double neutron star (DNS) and neutron star-white dwarf (NS-WD) systems respectively. I find a mass cutoff at 2 Msolar for NSs with WD companions, which establishes a firm lower bound for the maximum mass of NSs.

  14. Measuring neutron star masses and radii using NICER observations of X-ray oscillations

    Science.gov (United States)

    Lamb, Frederick K.; Miller, M. Coleman

    2016-04-01

    Precise and reliable simultaneous measurements of the mass and radius of several neutron stars with different masses would provide valuable guidance for improving models of the properties of cold dense matter. The prime scientific goal of the Neutron star Interior Composition ExploreR (NICER) is to make such measurements by fitting energy-dependent waveform models to the thermal X-ray oscillations observed from rotation-powered millisecond pulsars. These oscillations are thought to be produced as hotter regions of the stellar surface near one or both of the star’s magnetic poles rotate around the star at the star's spin frequency. We first discuss the phenomenology and modeling of these oscillations. We then present the results of parameter estimation studies using synthetic waveform data and Bayesian statistical methods. The synthetic and model waveforms used in this study were computed using the X-ray spectra and radiation beaming patterns given by models of the cool hydrogen atmospheres that NICER is expected to observe. Finally, we discuss the causes and expected sizes of the uncertainties in radius and mass estimates that will be made by NICER using this method.

  15. Properties of Rotating Neutron Star

    Directory of Open Access Journals (Sweden)

    Shailesh K. Singh

    2015-08-01

    Full Text Available Using the nuclear equation of states for a large variety of relativistic and non-relativistic force parameters, we calculate the static and rotating masses and radii of neutron stars. From these equation of states, we evaluate the properties of rotating neutron stars, such as rotational frequencies, moment of inertia, quadrupole deformation parameter, rotational ellipticity and gravitational wave strain amplitude. The estimated gravitational wave strain amplitude of the star is found to be~sim 10-23.

  16. Low mass binary neutron star mergers: Gravitational waves and neutrino emission

    Science.gov (United States)

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

    2016-02-01

    Neutron star mergers are among the most promising sources of gravitational waves for advanced ground-based detectors. These mergers are also expected to power bright electromagnetic signals, in the form of short gamma-ray bursts, infrared/optical transients powered by r-process nucleosynthesis in neutron-rich material ejected by the merger, and radio emission from the interaction of that ejecta with the interstellar medium. Simulations of these mergers with fully general relativistic codes are critical to understand the merger and postmerger gravitational wave signals and their neutrinos and electromagnetic counterparts. In this paper, we employ the Spectral Einstein Code to simulate the merger of low mass neutron star binaries (two 1.2 M⊙ neutron stars) for a set of three nuclear-theory-based, finite temperature equations of state. We show that the frequency peaks of the postmerger gravitational wave signal are in good agreement with predictions obtained from recent simulations using a simpler treatment of gravity. We find, however, that only the fundamental mode of the remnant is excited for long periods of time: emission at the secondary peaks is damped on a millisecond time scale in the simulated binaries. For such low mass systems, the remnant is a massive neutron star which, depending on the equation of state, is either permanently stable or long lived (i.e. rapid uniform rotation is sufficient to prevent its collapse). We observe strong excitations of l =2 , m =2 modes, both in the massive neutron star and in the form of hot, shocked tidal arms in the surrounding accretion torus. We estimate the neutrino emission of the remnant using a neutrino leakage scheme and, in one case, compare these results with a gray two-moment neutrino transport scheme. We confirm the complex geometry of the neutrino emission, also observed in previous simulations with neutrino leakage, and show explicitly the presence of important differences in the neutrino luminosity, disk

  17. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    Science.gov (United States)

    Bozzo, E.; Oskinova, L.; Feldmeier, A.; Falanga, M.

    2016-05-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the nonstationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total timescale of several hours), the transitions of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the nonstationary wind. The X-ray luminosity released by the system is computed at each time step by taking into account the relevant physical processes occurring in the different accretion regimes. Synthetic lightcurves are derived and qualitatively compared with those observed from classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. Although a number of simplifications are assumed in these calculations, we show that taking into account the effects of the centrifugal and magnetic inhibition of accretion significantly reduces the average X-ray luminosity expected for any neutron star wind-fed binary. The present model calculations suggest that long spin periods and stronger magnetic fields are favored in order to reproduce the peculiar behavior of supergiant fast X-ray transients in the X-ray domain.

  18. Probing thermonuclear burning on accreting neutron stars

    NARCIS (Netherlands)

    Keek, L.

    2008-01-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes

  19. 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.

  20. Probing thermonuclear burning on accreting neutron stars

    OpenAIRE

    Keek, L.

    2008-01-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one seco...

  1. A new view on the maximum mass of differentially rotating neutron stars

    CERN Document Server

    Gondek-Rosinska, Dorota; Villain, Loic; Ansorg, Marcus; Kucaba, Marcin

    2016-01-01

    We study the main astrophysical properties of differentially rotating neutron stars described as stationary and axisymmetric configurations of a moderately stiff $\\Gamma=2$ polytropic fluid. The high level of accuracy and of stability of our relativistic multidomain pseudo-spectral code enables us to explore the whole solution space for broad ranges of the degree of differential rotation, but also of the stellar density and oblateness. Staying within an astrophysicaly motivated range of rotation profiles, we investigate the characteristics of neutron stars with maximal mass for all types of families of differentially rotating relativistic objects identified in a previous article Ansorg, Gondek-Rosinsla, Villain (2009). We find that the maximum mass depends on both the degree of differential rotation and on the type of solution. It turns out that the maximum allowed mass can be up to 4 times higher than what it is for non-rotating stars with the same equation of state. Such values are obtained for a modest deg...

  2. Low mass binary neutron star mergers : gravitational waves and neutrino emission

    CERN Document Server

    Foucart, Francois; Duez, Matthew D; O'Connor, Evan; Ott, Christian D; Roberts, Luke; Kidder, Lawrence E; Lippuner, Jonas; Pfeiffer, Harald P; Scheel, Mark A

    2015-01-01

    Neutron star mergers are among the most promising sources of gravitational waves for advanced ground-based detectors. These mergers are also expected to power bright electromagnetic signals, in the form of short gamma-ray bursts, infrared/optical transients, and radio emission. Simulations of these mergers with fully general relativistic codes are critical to understand the merger and post-merger gravitational wave signals and their neutrinos and electromagnetic counterparts. In this paper, we employ the SpEC code to simulate the merger of low-mass neutron star binaries (two $1.2M_\\odot$ neutron stars) for a set of three nuclear-theory based, finite temperature equations of state. We show that the frequency peaks of the post-merger gravitational wave signal are in good agreement with predictions obtained from simulations using a simpler treatment of gravity. We find, however, that only the fundamental mode of the remnant is excited for long periods of time: emission at the secondary peaks is damped on a milli...

  3. Hadron star models. [neutron stars

    Science.gov (United States)

    Cohen, J. M.; Boerner, G.

    1974-01-01

    The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

  4. Pulsar J0453+1559: A Double Neutron Star System with a Large Mass Asymmetry

    CERN Document Server

    Martinez, J G; Freire, P C C; Deneva, J S; Jenet, F A; McLaughlin, M A; Bagchi, M; Bates, S D; Ridolfi, A

    2015-01-01

    To understand the nature of supernovae and neutron star (NS) formation, as well as binary stellar evolution and their interactions, it is important to probe the distribution of NS masses. Until now, all double NS (DNS) systems have been measured to have a mass ratio close to unity (q $\\geq$ 0.91). Here we report the measurement of the individual masses of the 4.07-day binary pulsar J0453+1559 from measurements of the rate of advance of periastron and Shapiro delay: The mass of the pulsar is 1.559(5) $M_{\\odot}$ and that of its companion is 1.174(4) $M_{\\odot}$; q = 0.75. If this companion is also a neutron star (NS), as indicated by the orbital eccentricity of the system (e=0.11), then its mass is the smallest precisely measured for any such object. The pulsar has a spin period of 45.7 ms and a spin derivative of 1.8616(7) x$10^-19$; from these we derive a characteristic age of ~ 4.1 x $10^9$ years and a magnetic field of ~ 2.9 x $10^9$ G,i.e, this pulsar was mildly recycled by accretion of matter from the pr...

  5. Detecting and Measuring the Masses of Isolated Black Holes and Neutron Stars through Astrometric Microlensing

    Science.gov (United States)

    Sahu, Kailash

    2013-10-01

    We propose a 3-year program of monitoring of 12 fields in the Galactic bulge, containing a total of 1.5 million stars down to V=28. Our primary aim is to detect microlensing events caused by non-luminous isolated black holes {BHs} and neutron stars {NSs} in the Galactic disk and bulge.The unique capability of HST imaging for microlensing observations is the addition of high-precision astrometry, allowing detection of the astrometric shift of the source during the event. Combined with the lens parallax, provided by the HST event light curve, the astrometric shift provides a direct measurement of the lens mass. We will detect 120 microlensing events, of which 45% will show astrometric deflections, leading to direct determinations of the lens masses. Of these, about 18 lenses are expected to be BHs and 14 of them NSs, along with about 22 events due to main-sequence stars.To date, BH and NS masses have been directly measured only in binaries; no isolated BH has been detected unambiguously within our Galaxy. A survey of the scope proposed here is the only means available at present for measuring the mass function of isolated BHs and NSs, and moreover one that is normalized to that of luminous stars. The results will provide a quantitative estimate of the mass content in the form of stellar remnants in the young Galactic disk and old bulge, and important constraints on SN/GRB explosion mechanisms that produce NSs and BHs.Our data will also be useful for other investigations, including a more accurate determination of the microlensing optical depth, faint variable stars, bulge proper motions and kinematics, and a deep luminosity function of the disk and bulge stars.

  6. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    CERN Document Server

    Bozzo, E; Feldmeier, A; Falanga, M

    2016-01-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the non-stationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total time scale of several hours), the transition of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the non-stationary wind. Th...

  7. Modeling Equal and Unequal Mass Binary Neutron Star Mergers Using Public Codes

    CERN Document Server

    De Pietri, Roberto; Maione, Francesco; Löffler, Frank

    2015-01-01

    We present three-dimensional simulations of the dynamics of binary neutron star (BNS) mergers from the late stage of the inspiral process up to $\\sim 20$ ms after the system has merged, either to form a hyper-massive neutron star (NS) or a rotating black hole (BH). We investigate five equal-mass models of total gravitational mass $2.207$, $2.373$, $2.537$, $2.697$ and $2.854 M_\\odot$, respectively, and four unequal mass models with $M_{\\mathrm{ADM}}\\simeq 2.53\\ M_\\odot$ and $q\\simeq 0.94$, $0.88$, $0.82$, and $0.77$ (where $q = M^{(1)}/M^{(2)}$ is the mass ratio). We use a semi-realistic equation of state (EOS) namely, the seven-segment piece-wise polytropic SLyPP with a thermal component given by $\\Gamma_{th} = 1.8$. We have also compared the resulting dynamics (for one model) using both, the BSSN-NOK and CCZ4 methods for the evolution of the gravitational sector, and also different reconstruction methods for the matter sector, namely PPM, WENO and MP5. Our results show agreement and high resolution, but sup...

  8. The Magnetospheres of (Accreting Neutron Stars

    Directory of Open Access Journals (Sweden)

    Wilms J.

    2014-01-01

    Full Text Available I give an overview of the most important observational tools to study the magnetospheres of accreting neutron stars, with a focus on accreting neutron stars in high mass X-ray binary systems. Topics covered are the different types of accretion onto neutron stars and the structure of the accretion column, and how models for these can be tested with observations.

  9. Binary Neutron Stars with Generic Spin, Eccentricity, Mass ratio, and Compactness - Quasi-equilibrium Sequences and First Evolutions

    CERN Document Server

    Dietrich, Tim; Johnson-McDaniel, Nathan K; Bernuzzi, Sebastiano; Markakis, Charalampos M; Bruegmann, Bernd; Tichy, Wolfgang

    2015-01-01

    Information about the last stages of a binary neutron star inspiral and the final merger can be extracted from quasi-equilibrium configurations and dynamical evolutions. In this article, we construct quasi-equilibrium configurations for different spins, eccentricities, mass ratios, compactnesses, and equations of state. For this purpose we employ the SGRID code, which allows us to construct such data in previously inaccessible regions of the parameter space. In particular, we consider spinning neutron stars in isolation and in binary systems; we incorporate new methods to produce highly eccentric and eccentricity reduced data; we present the possibility of computing data for significantly unequal-mass binaries; and we create equal-mass binaries with individual compactness up to 0.23. As a proof of principle, we explore the dynamical evolution of three new configurations. First, we simulate a $q=2.06$ mass ratio which is the highest mass ratio for a binary neutron star evolved in numerical relativity to date. ...

  10. Lense-Thirring precession in neutron-star low-mass X-ray binaries

    Science.gov (United States)

    Homan, Jeroen

    Quasi-periodic oscillations (QPOs) with low frequencies (0.01-70 Hz) have been observed in the X-ray light curves of most neutron-star and black-hole low-mass X-ray binaries. Despite having been discovered more than 25 years ago, their origin is still not well understood. Similarities between the low-frequency QPOs in the two types of systems suggest that they have a common origin in the accretion flows around black holes and neutron stars. Some of the proposed models that attempt to explain low- frequency QPOs invoke a General Relativistic effect known as Lense-Thirring precession (or "frame dragging"). However, for Lense-Thirring precession to produce substantial modulations of the X-ray flux through relativistic beaming and gravitational lensing, the rotation axis of the inner part of the accretion disk needs to have a substantial tilt (10-20 degrees) with respect to the spin axis of the compact object. We argue that observational evidence for such titled inner accretion disks can be found in the variability of neutron- star low-mass X-ray binaries that are viewed at inclination angles of 60-80 degrees. In these systems low-frequency QPOs at ~0.1-15 Hz are observed that modulate the emission from the neutron star by quasi-periodic obscuration, presumably by a titled inner disc. The goal of our proposed program is to test whether the frequency evolution and spectral state dependence of these QPOs is similar to what is observed for the low-frequency QPOs that are observed in lower-inclination neutron-star X-ray binaries. To make such a comparison, we need to better characterize the properties and behavior of these QPOs. Our study will make use of almost 1300 RXTE observations of 11 sources, totaling 5.7 Ms of data. Signatures of strong gravity have long been sought after in accreting compact objects. While strong evidence from spectral features has emerged in the last decade (e.g. gravitationally broadened iron emission lines), there have only been hints of such

  11. Neutron star moments of inertia

    Science.gov (United States)

    Ravenhall, D. G.; Pethick, C. J.

    1994-01-01

    An approximation for the moment of inertia of a neutron star in terms of only its mass and radius is presented, and insight into it is obtained by examining the behavior of the relativistic structural equations. The approximation is accurate to approximately 10% for a variety of nuclear equations of state, for all except very low mass stars. It is combined with information about the neutron-star crust to obtain a simple expression (again in terms only of mass and radius) for the fractional moment of inertia of the crust.

  12. Black hole-neutron star mergers at realistic mass ratios: Equation of state and spin orientation effects

    CERN Document Server

    Foucart, Francois; Duez, Matthew D; Kidder, Lawrence E; MacDonald, Ilana; Ott, Christian D; Pfeiffer, Harald P; Scheel, Mark A; Szilagyi, Bela; Teukolsky, Saul A

    2012-01-01

    Black hole-neutron star mergers resulting in the disruption of the neutron star and the formation of an accretion disk and/or the ejection of unbound material are prime candidates for the joint detection of gravitational-wave and electromagnetic signals when the next generation of gravitational-wave detectors comes online. However, the disruption of the neutron star and the properties of the post-merger remnant are very sensitive to the parameters of the binary. In this paper, we study the impact of the radius of the neutron star and the alignment of the black hole spin for systems within the range of mass ratio currently deemed most likely for field binaries (M_BH ~ 7 M_NS) and for black hole spins large enough for the neutron star to disrupt (J/M^2=0.9). We find that: (i) In this regime, the merger is particularly sensitive to the radius of the neutron star, with remnant masses varying from 0.3M_NS to 0.1M_NS for changes of only 2 km in the NS radius; (ii) 0.01-0.05M_sun of unbound material can be ejected w...

  13. Neutron star structure from QCD

    Science.gov (United States)

    Fraga, Eduardo S.; Kurkela, Aleksi; Vuorinen, Aleksi

    2016-03-01

    In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.

  14. Neutron star structure from QCD

    CERN Document Server

    Fraga, Eduardo S; Vuorinen, Aleksi

    2016-01-01

    In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.

  15. Neutron star structure from QCD

    Energy Technology Data Exchange (ETDEWEB)

    Fraga, Eduardo S. [Universidade Federal do Rio de Janeiro, Instituto de Fisica, Rio de Janeiro, RJ (Brazil); Kurkela, Aleksi [PH-TH, Case C01600, CERN, Theory Division, Geneva (Switzerland); University of Stavanger, Faculty of Science Technology, Stavanger (Norway); Vuorinen, Aleksi [University of Helsinki, Helsinki Institute of Physics and Department of Physics (Finland)

    2016-03-15

    In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities. (orig.)

  16. Neutron stars versus black holes: probing the mass gap with LIGO/Virgo

    CERN Document Server

    Littenberg, Tyson B; Coughlin, Scott; Kalogera, Vicky; Holz, Daniel E

    2015-01-01

    The inspirals and mergers of binary systems comprised of black holes (BHs) and/or neutron stars (NSs) are expected to be abundant sources for ground-based gravitational-wave (GW) detectors. We assess the capabilities of Advanced LIGO and Virgo to measure component masses using inspiral waveform models which include spin-precession effects by studying a large ensemble of plausible GW sources. We make quantitative predictions for how well LIGO and Virgo will be able to distinguish between black holes and neutron stars and appraise the prospect of using LIGO/Virgo observations to definitively confirm, or reject, the existence of a putative "mass gap" between NSs ($m\\leq3\\ M_\\odot$) and BHs ($m\\geq 5\\ M_\\odot$). We find sources with the smaller mass component satisfying $m_2 \\lesssim1.5\\ M_\\odot$ to be unambiguously identified as containing at least one NS, while systems with $m_2\\gtrsim6\\ M_\\odot$ will be confirmed binary BHs. However, binary BHs with $m_2<5\\ M_\\odot$ (i.e., in the gap) cannot be distinguishe...

  17. Neutron star mass limit at 2M{sub ⊙} supports the existence of a CEP

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez-Castillo, D. [JINR Dubna, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); Benic, S. [University of Zagreb, Department of Physics, Zagreb (Croatia); Blaschke, D. [JINR Dubna, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); National Research Nuclear University (MEPhI), Moscow (Russian Federation); University of Wroclaw, Institute of Theoretical Physics, Wroclaw (Poland); Han, Sophia [University of Tennessee, Department of Physics and Astronomy, Knoxville, TN (United States); Oak Ridge National Laboratory, Physics Division, Oak Ridge, TN (United States); Typel, S. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany)

    2016-08-15

    We point out that the very existence of a ''horizontal branch'' in the mass-radius characteristics for neutron stars indicates a strong first-order phase transition and thus supports the existence of a critical endpoint (CEP) of first-order phase transitions in the QCD phase diagram. This branch would sample a sequence of hybrid stars with quark matter core, leading to the endpoint of stable compact star configurations with the highest possible baryon densities. Since we know of the existence of compact stars with 2M{sub ⊙}, this hypothetical branch has to lie in the vicinity of this mass value, if it exists. We report here a correlation between the maximal radius of the horizontal branch and the pressure at the onset of hadron-to-quark matter phase transition, which is likely to be a universal quantity of utmost relevance to the upcoming experiments with heavy-ion collisions at NICA and FAIR. (orig.)

  18. The Fate of Merging Neutron Stars

    Science.gov (United States)

    Kohler, Susanna

    2017-08-01

    A rapidly spinning, highly magnetized neutron star is one possible outcome when two smaller neutron stars merge. [Casey Reed/Penn State University]When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us.Neutron Star or Black Hole?So far, the only systems from which weve detected gravitational waves are merging black holes. But other compact-object binaries exist and are expected to merge on observable timescales in particular, binary neutron stars. When two neutron stars merge, the resulting object falls into one of three categories:a stable neutron star,a black hole, ora supramassive neutron star, a large neutron star thats supported by its rotation but will eventually collapse to a black hole after it loses angular momentum.Histograms of the initial (left) and final (right) distributions of objects in the authors simulations, for five different equations of state. Most cases resulted primarily in the formation of neutron stars (NSs) or supramassive neutron stars (sNSs), not black holes (BHs). [Piro et al. 2017]Whether a binary-neutron-star merger results in another neutron star, a black hole, or a supramassive neutron star depends on the final mass of the remnant and what the correct equation of state is that describes the interiors of neutron stars a longstanding astrophysical puzzle.In a recent study, a team of scientists led by Anthony Piro (Carnegie Observatories) estimated which of these outcomes we should expect for mergers of binary neutron stars. The teams results along with future observations of binary neutron stars may help us to eventually pin down the equation of state for neutron stars.Merger OutcomesPiro and collaborators used relativistic calculations of spinning and non-spinning neutron stars to estimate the mass range that neutron stars would have for several different realistic equations of

  19. High Mass X-ray Binaries: Progenitors of double neutron star systems

    CERN Document Server

    Chaty, Sylvain

    2015-01-01

    In this review I briefly describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. A previously unknown population of HMXBs hosting supergiant stars has been revealed in the last years, with multi-wavelength campaigns including high energy (INTEGRAL, Swift, XMM, Chandra) and optical/infrared (mainly ESO) observations. This population is divided between obscured supergiant HMXBs, and supergiant fast X-ray transients (SFXTs), characterized by short and intense X-ray flares. I discuss the characteristics of these types of supergiant HMXBs, propose a scenario describing the properties of these high-energy sources, and finally show how the observations can constrain the accretion models (e.g. clumpy winds, magneto-centrifugal barrier, transitory accretion disc, etc). Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of double neutron star systems,...

  20. Reassessing The Fundamentals: New Constraints on the Evolution, Ages and Masses of Neutron Stars

    CERN Document Server

    Kiziltan, Bulent

    2011-01-01

    The ages and masses of neutron stars (NSs) are two fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these two derived parameters play an important role in understanding of advanced stages of stellar evolution and the physics that govern relevant processes. Here I summarize new constraints on the ages and masses of NSs with an evolutionary perspective. I show that the observed P-Pdot demographics is more diverse than what is theoretically predicted for the standard evolutionary channel. In particular, standard recycling followed by dipole spin-down fails to reproduce the population of millisecond pulsars with higher magnetic fields (B > 4 x 10^{8} G) at rates deduced from observations. A proper inclusion of constraints arising from binary evolution and mass accretion offers a more realistic insight into the age distribution. By analytically implementing these constraints, I propose a "modified" spin-down age for millis...

  1. Constraints on the Symmetry Energy Using the Mass-Radius Relation of Neutron Stars

    CERN Document Server

    Lattimer, James M

    2014-01-01

    The nuclear symmetry energy is intimately connected with nuclear astrophysics. This contribution focuses on the estimation of the symmetry energy from experiment and how it is related to the structure of neutron stars. The most important connection is between the radii of neutron stars and the pressure of neutron star matter in the vicinity of the nuclear saturation density $n_s$. This pressure is essentially controlled by the nuclear symmetry energy parameters $S_v$ and $L$, the first two coefficients of a Taylor expansion of the symmetry energy around $n_s$. We discuss constraints on these parameters that can be found from nuclear experiments. We demonstrate that these constraints are largely model-independent by deriving them qualitatively from a simple nuclear model. We also summarize how recent theoretical studies of pure neutron matter can reinforce these constraints. To date, several different astrophysical measurements of neutron star radii have been attempted. Attention is focused on photospheric rad...

  2. Mass Fraction of 13C-Pocket in Metal-Poor AGB Stars and the Primary Nature of Neutron Source

    Institute of Scientific and Technical Information of China (English)

    CUI Dong-Nuan; GENG Yuan-Yuan; CUI Wen-Yuan; ZHANG Bo

    2009-01-01

    Chemical abundances of very metal-poor s-rich stars contain excellent information to set new constraints on models of neutron-capture processes at low metalficity.Using the parametric approach based on the radiative s-process nucleosynthesis model,we obtain the mass fraction q of 13 C-pocket,the overlap factor r,the neutron exposure per interpulse △r,and the component coefficients of the s-process and the r-process for 25 s-rich stars,respectively. We find that q deduced for the lead stars is comparable to the overlap factor r,which is larger than the standard case (hereafter ST case) of the AGB model (q~0.05) about 10 times,and △r are about 10 times smaller than the ST case (△r = 7.0 mbarn-1).Although the two parameters obtained for the lead stars are very different from the ST case of the AGB stellar model,it is worth noting that the total amounts of 13C in metal-poor condition are close to the ST case.The above relation is a significant evidence for the primary nature of the neutron source and the lead stars could be polluted by low-mass AGB stars.Because interpulse period declines with increasing stellar mass,for high-mass A GB star,the neutron irradiation may be terminated due to their shorter interpulse period.Thus the neutron exposure per interpulse of the larger AGB stars should be about 10 times smaller than the ST case.In this case,the primary nature of the neutron source also exists.

  3. BPS Skyrmions as neutron stars

    CERN Document Server

    Adam, C; Sanchez-Guillen, J; Vazquez, R; Wereszczynski, A

    2014-01-01

    The BPS Skyrme model has been demonstrated already to provide a physically intriguing and quantitatively reliable description of nuclear matter. Indeed, the model has both the symmetries and the energy-momentum tensor of a perfect fluid, and thus represents a field theoretic realization of the "liquid droplet" model of nuclear matter. In addition, the classical soliton solutions together with some obvious corrections (spin-isospin quantization, Coulomb energy, proton-neutron mass difference) led to an accurate modeling of nuclear binding energies for heavier nuclei. These results lead to the rather obvious proposal to try to describe also neutron stars by the BPS Skyrme model coupled to gravity. We find that the resulting self-gravitating BPS Skyrmions provide an excellent description of neutron stars when the parameter values of the model are extracted from nuclear physics. Specifically, the maximum possible mass of a neutron star before black-hole formation sets in is several solar masses, the precise value...

  4. Neutron Stars and Pulsars

    CERN Document Server

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  5. Neutron stars - General review

    Science.gov (United States)

    Cameron, A. G. W.; Canuto, V.

    1974-01-01

    A review is presented of those properties of neutron stars upon which there is general agreement and of those areas which currently remain in doubt. Developments in theoretical physics of neutron star interiors are summarized with particular attention devoted to hyperon interactions and the structure of interior layers. Determination of energy states and the composition of matter is described for successive layers, beginning with the surface and proceeding through the central region into the core. Problems encountered in determining the behavior of matter in the ultra-high density regime are discussed, and the effects of the magnetic field of a neutron star are evaluated along with the behavior of atomic structures in the field. The evolution of a neutron star is outlined with discussion centering on carbon detonation, cooling, vibrational damping, rotation, and pulsar glitches. The role of neutron stars in cosmic-ray propagation is considered.

  6. Systematics of dynamical mass ejection, nucleosynthesis, and radioactively powered electromagnetic signals from neutron-star mergers

    CERN Document Server

    Bauswein, A; Janka, H -T

    2013-01-01

    Neutron star (NS) mergers can eject considerable amounts of neutron-rich matter, allowing for r-processing. The radioactive decay of the products heats the ejecta and makes them potentially observable as a source of thermal electromagnetic radiation. We investigate systematically the dynamical mass ejection during the NS collision in dependence on uncertain properties of the nuclear equation of state (EoS) by using 40 representative, microphysical EoSs in relativistic merger simulations. The NS compactness, characterized by the radius R_1.35 of nonrotating NSs of 1.35 Msun, is the crucial parameter that determines the ejecta mass. NSs with smaller radii R_1.35 ("soft"' EoS) collide more violently and eject systematically higher masses. These range from ~10^-3 Msun to ~10^-2 Msun for symmetric 1.35-1.35 Msun binaries with R_1.35 between 16 km and 11 km, and from ~5*10^-3 Msun to ~2*10^-2 Msun for asymmetric 1.2-1.5 Msun binaries. Correspondingly, the bolometric peak luminosities of the optical transients vary ...

  7. Accuracy in measuring the neutron star mass in gravitational wave parameter estimates for nonspinning compact binaries

    Science.gov (United States)

    Cho, Hee-Suk

    2015-09-01

    In gravitational wave (GW) data analysis, the parameter estimate is performed to find the physical parameters of GW sources. The result of the parameter estimate is given by a posterior probability density function, and the measurement errors can be computed by using the Fisher matrix method. Using this method, we investigate the accuracy in estimates of neutron star (NS) masses ( M NS) for GWs emitted from merging compact binaries. As GW sources, we consider nonspinning binaries in which the primary component is assumed to be a NS and the companion is assumed to be a NS or a stellar-mass black hole (BH). Adopting GW signals with a signal-to-noise ratio of 10 for Advanced LIGO (Laser Interferometer Gravitational wave Observatory) sensitivity, we calculate measurement errors (σ) of M NS. We find that the errors strongly depend on the mass ratio of the companion mass ( M com) to the NS mass ( M NS). For NS-NS binaries, the fractional errors (σ/ M NS) are larger than 10% only in the symmetric mass region. For BH-NS binaries, the fractional errors tend to decrease with increasing mass ratio ( M com/ M NS), and the measurement accuracies are better than those for NS-NS binaries. In this case, the errors are always smaller than ~ 3%.

  8. The fate of a neutron star just below the minimum mass does it explode?

    CERN Document Server

    Sumiyoshi, K; Suzuki, H; Hillebrandt, W

    1997-01-01

    First results of numerical simulations are presented which compute the dynamical evolution of a neutron star with a mass slightly below the minimum stable mass by means of a new implicit (general relativistic) hydrodynamic code. We show that such a star first undergoes a phase of quasi-static expansion, caused by slow nuclear $\\beta$-decays, lasting for about 20 seconds, but then explodes violently. The kinetic energy of the explosion is around $10^{49} erg$, the peak luminosity in electron anti-neutrinos is of order $10^{52} erg/s$, and the thermodynamic conditions of the expanding matter are favorable for r-process nucleosynthesis. These results are obtained for the Harrison-Wheeler equation of state and a simple and, possibly, unrealistic treatment of $\\beta$-decay rates and nuclear fission, which were adopted for comparison with previous works. However, we do not expect that the outcome will change qualitatively if more recent nuclear input physics used. Although our study does not rely on a specific scen...

  9. Neutron Star Mass-Radius Constraints of the Quiescent Low-mass X-ray Binaries X7 and X5 in the Globular Cluster 47 Tuc

    CERN Document Server

    Bogdanov, Slavko; Özel, Feryal; Güver, Tolga

    2016-01-01

    We present Chandra ACIS-S sub-array observations of the quiescent neutron star low-mass X-ray binaries X7 and X5 in the globular cluster 47 Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the neutron star radius and mass of these neutron stars. Modeling the thermal emission from the neutron star surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the neutron star in X7 a radius of $R=11.1^{+0.8}_{-0.7}$ km for an assumed stellar mass of $M=1.4$ M$_{\\odot}$ (68% C.L.). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of $R=9.6^{+0.9}_{-1.1}$ km, assuming a hydrogen atmosphere and a mass of $M=1.4$ M$_{\\odot}$. When combined with all other existing spec...

  10. Oscillations in neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Hoeye, Gudrun Kristine

    1999-07-01

    We have studied radial and nonradial oscillations in neutron stars, both in a general relativistic and non-relativistic frame, for several different equilibrium models. Different equations of state were combined, and our results show that it is possible to distinguish between the models based on their oscillation periods. We have particularly focused on the p-, f-, and g-modes. We find oscillation periods of II approx. 0.1 ms for the p-modes, II approx. 0.1 - 0.8 ms for the f-modes and II approx. 10 - 400 ms for the g-modes. For high-order (l (>{sub )} 4) f-modes we were also able to derive a formula that determines II{sub l+1} from II{sub l} and II{sub l-1} to an accuracy of 0.1%. Further, for the radial f-mode we find that the oscillation period goes to infinity as the maximum mass of the star is approached. Both p-, f-, and g-modes are sensitive to changes in the central baryon number density n{sub c}, while the g-modes are also sensitive to variations in the surface temperature. The g-modes are concentrated in the surface layer, while p- and f-modes can be found in all parts of the star. The effects of general relativity were studied, and we find that these are important at high central baryon number densities, especially for the p- and f-modes. General relativistic effects can therefore not be neglected when studying oscillations in neutron stars. We have further developed an improved Cowling approximation in the non-relativistic frame, which eliminates about half of the gap in the oscillation periods that results from use of the ordinary Cowling approximation. We suggest to develop an improved Cowling approximation also in the general relativistic frame. (Author)

  11. A new estimation method for mass of an isolated neutron star using gravitational waves

    CERN Document Server

    Ono, Kenji; Itoh, Yousuke

    2015-01-01

    We investigate a possibility of estimating mass of an isolated rapidly rotating neutron star (NS) from a continuous gravitational wave (GW) signal emitted by the NS. When the GW passes through the gravitational potential of the NS, the GW takes a slightly longer time to travel to an observer than it does in the absence of the NS. Such a time dilation effect holds also for photons and is often referred to as the gravitational time delay (or the Shapiro time delay). Correspondingly, the phase of the GW from the NS shifts due to the Coulomb type gravitational potential of the NS, and the resulting logarithmic phase shift depends on the mass, the spin frequency of the NS, and the distance to the NS. We show that the NS mass can, in principle, be obtained by making use of the phase shift difference between two modes of the continuous GW such as once and twice spin frequency modes induced by a freely precessing NS or a NS containing a pinned superfluid core. We estimate the measurement accuracy of the NS mass using...

  12. Temperature of neutron stars

    Science.gov (United States)

    Tsuruta, Sachiko

    2016-07-01

    We start with a brief introduction to the historical background in the early pioneering days when the first neutron star thermal evolution calculations predicted the presence of neutron stars hot enough to be observable. We then report on the first detection of neutron star temperatures by ROSAT X-ray satellite, which vindicated the earlier prediction of hot neutron stars. We proceed to present subsequent developments, both in theory and observation, up to today. We then discuss the current status and the future prospect, which will offer useful insight to the understanding of basic properties of ultra-high density matter beyond the nuclear density, such as the possible presence of such exotic particles as pion condensates.

  13. Using observations of millisecond pulsars to measure mass and radius of neutron stars and implications for equation of state of matter at high density

    CERN Document Server

    Leahy, Denis

    2010-01-01

    Millisecond pulsars are rapidly rotating neutron stars where general relativity plays a strong role in the propagation of light from the neutron star to observer. The observed X-ray pulse shapes carry information on the mass, radius and surface shape of the neutron star. Comparison of theoretical calculations of pulse shapes with observed pulse shapes can give useful constraints on neutron star properties. Then comparison with calculated properties giving an assumed equation of state (EOS) can confirm or rule out the assumed EOS.

  14. Evolution of Neutron Stars and Observational Constraints

    Directory of Open Access Journals (Sweden)

    Lattimer J.

    2010-10-01

    Full Text Available The structure and evolution of neutron stars is discussed with a view towards constraining the properties of high density matter through observations. The structure of neutron stars is illuminated through the use of several analytical solutions of Einstein’s equations which, together with the maximally compact equation of state, establish extreme limits for neutron stars and approximations for binding energies, moments of inertia and crustal properties as a function of compactness. The role of the nuclear symmetry energy is highlighted and constraints from laboratory experiments such as nuclear masses and heavy ion collisions are presented. Observed neutron star masses and radius limits from several techniques, such as thermal emissions, X-ray bursts, gammaray flares, pulsar spins and glitches, spin-orbit coupling in binary pulsars, and neutron star cooling, are discussed. The lectures conclude with a discusson of proto-neutron stars and their neutrino signatures.

  15. Neutron Star Matter

    CERN Document Server

    Wambach, Jochen

    2013-01-01

    In this presentation I discuss two aspects of the neutron-matter equation of state. One relates to the symmetry energy of nuclear matter and empirical constraints on its slope parameter at saturation density. The second deals with spatially inhomogeneous chiral phases of deconfined quark matter in the inner core of a neutron star.

  16. A Change in the Quiescent X-Ray Spectrum of the Neutron Star Low-mass X-Ray Binary MXB 1659-29

    NARCIS (Netherlands)

    E.M. Cackett; E.F. Brown; A. Cumming; N. Degenaar; J. Fridriksson; J. Homan; J.M. Miller; R. Wijnands

    2013-01-01

    The quasi-persistent neutron star low-mass X-ray binary MXB 1659-29 went into quiescence in 2001, and we have followed its quiescent X-ray evolution since. Observations over the first 4 yr showed a rapid drop in flux and temperature of the neutron star atmosphere, interpreted as cooling of the neutr

  17. The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657-415

    CERN Document Server

    Mason, A B; Norton, A J; Crowther, P A; Tauris, T M; Langer, N; Negueruela, I; Roche, P

    2011-01-01

    We report near-infrared radial velocity measurements of the recently identified donor star in the high mass X-ray binary system OAO 1657-415 obtained in the H band using ISAAC on the VLT. Cross-correlation methods were employed to construct a radial velocity curve with a semi-amplitude of $22.1 \\pm 3.5$ km s$^{-1}$. Combined with other measured parameters of this system this provides a dynamically determined neutron star mass of $1.4 \\pm 0.3 - 1.7 \\pm 0.3$ M$_{\\odot}$ and a mass of $14.2 \\pm 0.4 - 17.0 \\pm 0.7$ M$_{\\odot}$ for the Ofpe/WN9 highly evolved donor star. Lower and upper limits are obtained under the assumptions that the system is viewed edge on ($i=90^{\\circ}$ with $\\beta=0.86$) and that the donor fills its Roche lobe ($\\beta = 1$ with $i=70.3^\\circ$) respectively. OAO 1657-415 is an eclipsing High Mass X-ray binary pulsar with the largest eccentricity and orbital period of any within its class. Of the ten known eclipsing X-ray binary pulsars OAO 1657-415 becomes the eighth with a dynamically dete...

  18. Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

    CERN Document Server

    Waterhouse, A C; Wijnands, R; Brown, E F; Miller, J M; Altamirano, D; Linares, M

    2015-01-01

    Aql X-1 is a prolific transient neutron star low-mass X-ray binary that exhibits an accretion outburst approximately once every year. Whether the thermal X-rays detected in intervening quiescent episodes are the result of cooling of the neutron star or due to continued low-level accretion remains unclear. In this work we use Swift data obtained after the long and bright 2011 and 2013 outbursts, as well as the short and faint 2015 outburst, to investigate the hypothesis that cooling of the accretion-heated neutron star crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that the X-ray light curves and measured neutron star surface temperatures are consistent with the expectations of the crust cooling paradigm. By using a thermal evolution code, we find that ~1.2-3.2 MeV/nucleon of shallow heat release describes the observational data well, depending on the assumed mass-accretion rate and temperature of the stellar core. We find no evidence for varying strengths of this shallow heating aft...

  19. On the robustness of the r-process in neutron-star mergers against variations of nuclear masses

    Science.gov (United States)

    Mendoza-Temis, J. J.; Wu, M. R.; Martínez-Pinedo, G.; Langanke, K.; Bauswein, A.; Janka, H.-T.; Frank, A.

    2016-07-01

    r-process calculations have been performed for matter ejected dynamically in neutron star mergers (NSM), such calculations are based on a complete set of trajectories from a three-dimensional relativistic smoothed particle hydrodynamic (SPH) simulation. Our calculations consider an extended nuclear reaction network, including spontaneous, β- and neutron-induced fission and adopting fission yield distributions from the ABLA code. In this contribution we have studied the sensitivity of the r-process abundances to nuclear masses by using diferent mass models for the calculation of neutron capture cross sections via the statistical model. Most of the trajectories, corresponding to 90% of the ejected mass, follow a relatively slow expansion allowing for all neutrons to be captured. The resulting abundances are very similar to each other and reproduce the general features of the observed r-process abundance (the second and third peaks, the rare-earth peak and the lead peak) for all mass models as they are mainly determined by the fission yields. We find distinct differences in the predictions of the mass models at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r-process nuclei around neutron number N = 130.

  20. Dynamical mass ejection from the merger of asymmetric binary neutron stars: Radiation-hydrodynamics study in general relativity

    CERN Document Server

    Sekiguchi, Yuichiro; Kyutoku, Koutarou; Shibata, Masaru; Taniguchi, Keisuke

    2016-01-01

    We perform neutrino radiation-hydrodynamics simulations for the merger of asymmetric binary neutron stars in numerical relativity. Neutron stars are modeled by soft and moderately stiff finite-temperature equations of state (EOS). We find that the properties of the dynamical ejecta such as the total mass, neutron richness profile, and specific entropy profile depend on the mass ratio of the binary systems for a given EOS in a unique manner. For the soft EOS (SFHo), the total ejecta mass depends weakly on the mass ratio, but the average of electron number per baryon ($Y_e$) and specific entropy ($s$) of the ejecta decreases significantly with the increase of the degree of mass asymmetry. For the stiff EOS (DD2), with the increase of the mass asymmetry degree, the total ejecta mass significantly increases while the average of $Y_e$ and $s$ moderately decreases. We find again that only for the soft EOS (SFHo), the total ejecta mass exceeds $0.01M_\\odot$ irrespective of the mass ratio chosen in this paper. The ej...

  1. Double Neutron Stars: Evidence For Two Different Neutron-Star Formation Mechanisms

    OpenAIRE

    Heuvel, E. P. J. van den

    2007-01-01

    Six of the eight double neutron stars known in the Galactic disk have low orbital eccentricities (< 0.27) indicating that their second-born neutron stars received only very small velocity kicks at birth. This is similar to the case of the B-emission X-ray binaries, where a sizable fraction of the neutron stars received hardly any velocity kick at birth (Pfahl et al. 2002). The masses of the second-born neutron stars in five of the six low-eccentricity double neutron stars are remarkably low (...

  2. No Neutron Star Companion To The Lowest Mass SDSS White Dwarf

    CERN Document Server

    Agueros, Marcel; Camilo, Fernando; Kilic, Mukremin; Anderson, Scott; Freire, Paulo; Kleinman, Scot; Liebert, James; Silvestri, Nicole

    2009-01-01

    SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun; Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems. An optical search for J0917+4638's companion showed that it must be a compact object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to uncover a potential NS companion to the LMWD. No convincing pulsar signal is detected in our radio data. Our X-ray observation also failed to detect X-ray emission from J0917+4638's companion, while we would have detected any of the millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost certainly another WD.

  3. The Mass-Radius relation for Neutron Stars in $f(R)$ gravity

    CERN Document Server

    Capozziello, Salvatore; Farinelli, Ruben; Odintsov, Sergei D

    2016-01-01

    We discuss the Mass -Radius diagram for static neutron star models obtained by the numerical solution of modified Tolman-Oppenheimer-Volkoff equations in $f(R)$ gravity where the Lagrangians $f(R)=R+\\alpha R^2 (1+\\gamma R)$ and $f(R)=R^{1+\\epsilon }$ are adopted. Unlike the case of the perturbative approach previously reported, the solutions are constrained by the presence of an extra degree of freedom, coming from the trace of the field equations. In particular, the stiffness of the equation of state determines an upper limit on the central density $\\rho_c$ above which the the positivity condition of energy-matter tensor trace $T^{\\rm m}=\\rho - 3 p$ holds. In the case of quadratic f(R)-gravity, we find higher masses and radii at lower central densities with an inversion of the behavior around a pivoting $\\rho_c$ which depends on the choice of the equation of state. When considering the cubic corrections, we find solutions converging to the required asymptotic behavior of flat metric only for $\\gamma < 0$....

  4. Equation of State for Nucleonic and Hyperonic Neutron Stars with Mass and Radius Constraints

    CERN Document Server

    Tolos, Laura; Ramos, Angels

    2016-01-01

    We obtain a new equation of state for the nucleonic and hyperonic inner core of neutron stars that fulfills the 2$M_{\\odot}$ observations as well as the recent determinations of stellar radii below 13 km. The nucleonic equation of state is obtained from a new parametrization of the FSU2 relativistic mean-field functional that satisfies these latest astrophysical constraints and, at the same time, reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions. On the one hand, the equation of state of neutron star matter is softened around saturation density, which increases the compactness of canonical neutron stars leading to stellar radii below 13 km. On the other hand, the equation of state is stiff enough at higher densities to fulfill the 2$M_{\\odot}$ limit. By a slight modification of the parametrization, we also find that the constraints of 2$M_{\\odot}$ neutron stars with radii around 13 km are satisfied when hype...

  5. Mergers of neutron star black hole binaries with small mass ratios: nucleosynthesis, gamma-ray bursts and electromagnetic transients

    CERN Document Server

    Rosswog, S

    2005-01-01

    I discuss simulations of the coalescence of black hole neutron star binary systems with black hole masses between 14 and 20 \\msun. The calculations use a three-dimensional smoothed particle hydrodynamics code, a temperature-dependent, nuclear equation of state and a multi-flavor neutrino scheme. General relativistic effects are mimicked using the \\Pacz-Wiita pseudo-potential and gravitational radiation reaction forces. Opposite to previous, purely Newtonian calculations, in none of the explored cases episodic mass transfer occurs. The neutron star is always completely disrupted after most of its mass has been transferred directly into the hole. For black hole masses between 14 and 16 \\Msun an accretion disk forms, large parts of it, however, are inside the last stable orbit and therefore falling with large radial velocities into the hole. These disks are (opposite to the neutron star merger case) thin and -apart from a spiral shock- essentially cold. For higher mass black holes ($M_{\\rm BH} \\ge 18$ \\msun) alm...

  6. Main parameters of neutron stars from quasi-periodic oscillations in low mass X-ray binaries

    CERN Document Server

    Boshkayev, Kuantay; Muccino, Marco

    2016-01-01

    We investigate the kilohertz quasi-periodic oscillations of low-mass X-ray binaries within the Hartle-Thorne spacetime. On the basis the relativistic precession model we extract the total mass $M$, angular momentum $J$, and quadrupole moment $Q$ of a compact object in a low-mass X-ray binary by analyzing the data of the Z -source GX 5-1. In view of the recent neutron star model we compute the radius, angular velocity and other parameters of this source by imposing the observational and theoretical constraints on the mass-radius relation.

  7. Carbon neutron star atmospheres

    CERN Document Server

    Suleimanov, V F; Pavlov, G G; Werner, K

    2013-01-01

    The accuracy of measuring the basic parameters of neutron stars is limited in particular by uncertainties in chemical composition of their atmospheres. For example, atmospheres of thermally - emitting neutron stars in supernova remnants might have exotic chemical compositions, and for one of them, the neutron star in CasA, a pure carbon atmosphere has recently been suggested by Ho & Heinke (2009). To test such a composition for other similar sources, a publicly available detailed grid of carbon model atmosphere spectra is needed. We have computed such a grid using the standard LTE approximation and assuming that the magnetic field does not exceed 10^8 G. The opacities and pressure ionization effects are calculated using the Opacity Project approach. We describe the properties of our models and investigate the impact of the adopted assumptions and approximations on the emergent spectra.

  8. Exploration of Spin-down Rate of Neutron Star in High Mass X-ray Binaries

    CERN Document Server

    Dai, Hai-Lang; Li, Xiang-Dong

    2016-01-01

    We use the evolutionary population synthesis method to investigate the statistical properties of the wind-fed neutron star (NS) compact ($P_{\\rm orb}<10$ days) high-mass X-ray binaries (HMXBs) in our Galaxy, based on different spin-down models. We find that the spin-down rate in the supersonic propeller phase given \\textbf{by assuming that the surrounding material is treated as forming a quasi-static atmosphere} or \\textbf{by assuming that the characteristic velocity of matter and the typical Alfv$\\acute{e}$n velocity of material in the magnetospheric boundary layer are comparable to the sound speed in the external medium} is too low to produce the observed number of compact HMXBs. We also find that the models suggested \\textbf{by assuming that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius} and \\textbf{by simple integration of the magnetic torque over the magnetosphere} with a larger spin-down ...

  9. Neutrino Processes in Neutron Stars

    Science.gov (United States)

    Kolomeitsev, E. E.; Voskresensky, D. N.

    2010-10-01

    The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities). The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong interaction effects can be

  10. Atmospheres around Neutron Stars

    Science.gov (United States)

    Fryer, Chris L.; Benz, Willy

    1994-12-01

    Interest in the behavior of atmospheres around neutron stars has grown astronomically in the past few years. Some of this interest arrived in the wake of the explosion of Supernova 1987A and its elusive remnant; spawning renewed interest in a method to insure material ``fall-back'' onto the adolescent neutron star in an effort to transform it into a silent black hole. However, the bulk of the activity with atmospheres around neutron stars is concentrated in stellar models with neutron star, rather than white dwarf, cores; otherwise known as Thorne-Zytkow objects. First a mere seed in the imagination of theorists, Thorne-Zytkow objects have grown into an observational reality with an ever-increasing list of formation scenarios and observational prospects. Unfortunately, the analytic work of Chevalier on supernova fall-back implies that, except for a few cases, the stellar simulations of Thorne-Zytkow objects are missing an important aspect of physics: neutrinos. Neutrino cooling removes the pressure support of these atmospheres, allowing accretion beyond the canonical Eddington rate for these objects. We present here the results of detailed hydrodynamical simulations in one and two dimensions with the additional physical effects of neutrinos, advanced equations of state, and relativity over a range of parameters for our atmosphere including entropy and chemical composition as well as a range in the neutron star size. In agreement with Chevalier, we find, under the current list of formation scenarios, that the creature envisioned by Thorne and Zytkow will not survive the enormous appetite of a neutron star. However, neutrino heating (a physical effect not considered in Chevalier's analysis) can play an important role in creating instabilities in some formation schemes, leading to an expulsion of matter rather than rapid accretion. By placing scrutiny upon the formation methods, we can determine the observational prospects for each.

  11. Neutron drip transition in accreting and nonaccreting neutron star crusts

    CERN Document Server

    Chamel, N; Zdunik, J L; Haensel, P

    2015-01-01

    The neutron-drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density $\\rho_\\textrm{drip}$. This transition has been mainly studied under the cold catalyzed matter hypothesis. However, this assumption is unrealistic for accreting neutron stars. After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained. Moreover, we show that the neutron-drip transition occurs at lower density and pressure than those predicted within the mean-nucleus approximation. This transition is studied numerically for various initial composition of the ashes from X-ray bursts and superbursts using microscopic nuclear mass models.

  12. Spectral-Timing Analysis of Kilohetrz Quasi-Periodic Osciallations in Neutron Star Low-Mass X-ray Binaries

    Science.gov (United States)

    Troyer, Jon; Peille, Philippe; Cackett, Edward; Barret, Didier

    2017-08-01

    Kilohertz quasi-periodic oscillations or kHz QPOs are intensity variations that occur in the X-ray band observed in neutron star low-mass X-ray binary (LMXB) systems. In such systems, matter is transferred from a secondary low-mass star to a neutron star via the process of accretion. kHz QPOs occur on the timescale of the inner accretion flow and may carry signatures of the physics of strong gravity (c2 ~ GM/R) and possibly clues to constraining the neutron star equation of state (EOS). Both the timing behavior of kHz QPOs and the time-averaged spectra of these systems have been studied extensively. No model derived from these techniques has been able to illuminate the origin of kHz QPOs. Spectral-timing is an analysis technique that can be used to derive information about the nature of physical processes occurring within the accretion flow on the timescale of the kHz QPO. To date, kHz QPOs of (4) neutron star LMXB systems have been studied with spectral-timing techniques. We present a comprehensive study of spectral-timing products of kHz QPOs from systems where data is available in the RXTE archive to demonstrate the promise of this technique to gain insights regarding the origin of kHz QPOs. Specifically, we show correlated time-lags as a function of QPO frequency and energy for the various LMXB systems where kHz QPOs are detected.

  13. Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes

    Energy Technology Data Exchange (ETDEWEB)

    Stoica, S. [Horia Hulubei National Institute of Physics and Nuclear Engineering, PO Box MG-6, 76900 Bucharest-Magurele (Romania); Horia Hulubei Foundation, Atomistilor 407, Bucharest-Magurele (Romania)], E-mail: stoica@theory.nipne.ro; Pastrav, B. [Horia Hulubei National Institute of Physics and Nuclear Engineering, PO Box MG-6, 76900 Bucharest-Magurele (Romania)], E-mail: bpastrav@theory.nipne.ro; Horvath, J.E. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, 05508-900 Cidade Universitaria Sao Paulo, SP (Brazil)], E-mail: foton@astro.iag.usp.br; Allen, M.P. [CEFET-SP, R. Pedro Vicente 625, 01109-010 Caninde, Sao Paulo, SP (Brazil)

    2009-09-15

    The rates of axion emission by nucleon-nucleon bremsstrahlung are calculated with the inclusion of the full momentum contribution from a nuclear one pion exchange (OPE) potential. The contributions of the neutron-neutron (nn), proton-proton ( pp) and neutron-proton (np) processes in both the non-degenerate and degenerate limits are explicitly given. We find that the finite-momentum corrections to the emissivities are quantitatively significant for the non-degenerate regime and temperature-dependent, and should affect the existing axion mass bounds. The trend of these nuclear effects is to diminish the emissivities.

  14. High space velocities of single radio pulsars versus low orbital eccentricities and masses of double neutron stars: Evidence for two different neutron star formation mechanisms

    NARCIS (Netherlands)

    van den Heuvel, E.P.J.

    2010-01-01

    Radio pulsars tend to be high-velocity objects, which implies that the majority of them received a velocity kick of several hundreds of km s(-1) at birth. However, six of the eight known double neutron stars in the galactic disk have quite low orbital eccentricities (0.085-0.27), indicating - taking

  15. High space velocities of single radio pulsars versus low orbital eccentricities and masses of double neutron stars: Evidence for two different neutron star formation mechanisms

    NARCIS (Netherlands)

    van den Heuvel, E.P.J.

    2010-01-01

    Radio pulsars tend to be high-velocity objects, which implies that the majority of them received a velocity kick of several hundreds of km s(-1) at birth. However, six of the eight known double neutron stars in the galactic disk have quite low orbital eccentricities (0.085-0.27), indicating - taking

  16. On the conversion of neutron stars into quark stars

    CERN Document Server

    Pagliara, Giuseppe

    2013-01-01

    The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of $10^{53}$ erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also briefly discuss this scenario in connection with recent measurements of masses and radii of compact stars.

  17. Quark Deconfinement in Rotating Neutron Stars

    Directory of Open Access Journals (Sweden)

    Richard D. Mellinger

    2017-01-01

    Full Text Available In this paper, we use a three flavor non-local Nambu–Jona-Lasinio (NJL model, an improved effective model of Quantum Chromodynamics (QCD at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible existence of quark matter in the cores of rotating neutron stars (pulsars. In contrast to non-rotating neutron stars, whose particle compositions do not change with time (are frozen in, the type and structure of the matter in the cores of rotating neutron stars depends on the spin frequencies of these stars, which opens up a possible new window on the nature of matter deep in the cores of neutron stars. Our study shows that, depending on mass and rotational frequency, up to around 8% of the mass of a massive neutron star may be in the mixed quark-hadron phase, if the phase transition is treated as a Gibbs transition. We also find that the gravitational mass at which quark deconfinement occurs in rotating neutron stars varies quadratically with spin frequency, which can be fitted by a simple formula.

  18. Structures of Rotating Traditional Neutron Stars and Hyperon Stars in the Relativistic $\\sigma-\\omega$ Model

    CERN Document Server

    Wen, D; Wang, X; Ai, B; Liu, G; Dong, D; Liu, L; Wen, De-hua; Chen, Wei; Wang, Xian-ju; Ai, Bao-quan; Liu, Guo-tao; Dong, Dong-qiao; Liu, Liang-gang

    2003-01-01

    The influence of the rotation on the total masses and radii of the neutron stars are calculated by the Hartle's slow rotation formalism, while the equation of state is considered in a relativistic $\\sigma-\\omega$ model. Comparing with the observation, the calculating result shows that the double neutron star binaries are more like hyperon stars and the neutron stars of X-ray binaries are more like traditional neutron stars. As the changes of the mass and radius to a real neutron star caused by the rotation are very small comparing with the total mass and radius, one can see that Hartle's approximate method is rational to deal with the rotating neutron stars. If three property values: mass, radius and period are observed to the same neutron star, then the EOS of this neutron star could be decided entirely.

  19. Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust

    CERN Document Server

    Meisel, Z; Ahn, S; Bazin, D; Brown, B A; Browne, J; Carpino, J F; Chung, H; Cyburt, R H; Estradé, A; Famiano, M; Gade, A; Langer, C; Matoš, M; Mittig, W; Montes, F; Morrissey, D J; Pereira, J; Schatz, H; Schatz, J; Scott, M; Shapira, D; Sieja, K; Smith, K; Stevens, J; Tan, W; Tarasov, O; Towers, S; Wimmer, K; Winkelbauer, J R; Yurkon, J; Zegers, R G T

    2016-01-01

    We present the mass excesses of 59-64Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N=38. Additionally, we extend the S2n trend for chromium to N=40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-art shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g9/2 and d5/2 orbits for the neutron valence space. We employ our result for the mass of 64Cr in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A=64 isobaric...

  20. Jets from Merging Neutron Stars

    Science.gov (United States)

    Kohler, Susanna

    2016-06-01

    With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially

  1. The Neutron Star Zoo

    Science.gov (United States)

    Harding, Alice K.

    2014-01-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not

  2. Accuracy of Mass and Radius Determination for Neutron Stars in X-ray Bursters from Simulated LOFT Spectra

    Science.gov (United States)

    Majczyna, A.; Madej, J.; Różańska, A.; Należyty, M.

    2017-06-01

    We present a simulation of an X-ray spectrum of a hot neutron star, as would be seen by the LAD detector on board of LOFT satellite. We also compute a grid of theoretical spectra corresponding to a range of effective temperatures Teff and surface gravities log g with values corresponding to compact stars in Type I X-ray bursters. A neutron star with the mass M=1.64 M⊙ and the radius R=11.95 km (which yields the surface gravity log g=14.30 [cgs] and the surface redshift z=0.30) is used in simulation. Accuracy of mass and radius determination by fitting theoretical spectra to the observed one is found to be M=1.64+0.16-0.02 M⊙ and R=11.95+1.57-0.40 km (2σ). The confidence contours for these two variables are narrow but elongated, and therefore the resulting constraints on the EOS cannot be strong. Note, that in this paper we aim to discuss error contours of NS mass and radius, whereas discussion of EOS is beyond the scope of this work.

  3. Non-Spherical Models of Neutron Stars

    CERN Document Server

    Zubairi, O; Romero, A; Mellinger, R; Weber, F; Orsaria, M; Contrera, G

    2015-01-01

    Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present (such as for magnetars) and/or the pressure of the matter in the cores of neutron stars is non-isotropic (e.g., color superconducting). In this paper, we investigate the structure of non-spherical neutron stars in the framework of general relativity. Using a parameterized metric to model non-spherical mass distributions, we first derive a stellar structure equation for deformed neutron stars. Numerical investigations of this model equation show that the gravitational masses of deformed neutron stars depend rather strongly on the degree and type (oblate or prolate) of stellar deformation. In particular, we find that the mass of a neutron star increases with increasing oblateness but decreases with increasing prolateness. If this feature carries over to a full two-dimensional treatment of deformed neutron stars, this opens up the possibil...

  4. Determining neutron star masses and radii using energy-resolved waveforms of X-ray burst oscillations

    CERN Document Server

    Lo, Ka-Ho; Bhattacharyya, Sudip; Lamb, Frederick K

    2013-01-01

    Simultaneous, precise measurements of the mass $M$ and radius $R$ of neutron stars can yield uniquely valuable information about the still uncertain properties of cold matter at several times the density of nuclear matter. One method that could be used to measure $M$ and $R$ is to analyze the energy-dependent waveforms of the X-ray flux oscillations seen during some thermonuclear bursts from some neutron stars. These oscillations are thought to be produced by X-ray emission from hotter regions on the surface of the star that are rotating at or near the spin frequency of the star. Here we explore how well $M$ and $R$ could be determined by generating, and analyzing using Bayesian techniques, synthetic energy-resolved X-ray data that we produce assuming a future space mission having 2--30 keV energy coverage and an effective area of 10 m$^2$, such as the proposed \\textit{LOFT} or \\textit{AXTAR} missions. We find that if the hot spot is within 10$^\\circ$ of the rotation equator, both $M$ and $R$ can usually be d...

  5. A G2-QCD neutron star

    CERN Document Server

    Hajizadeh, Ouraman

    2016-01-01

    The determination of the properties of neutron stars from the underlying theory, QCD, is still an unsolved problem. This is mainly due to the difficulty to obtain reliable results for the equation of state for cold, dense QCD. As an alternative route to obtain qualitative insights, we determine the structure of a neutron star for a modified version of QCD: By replacing the gauge group SU(3) with the exceptional Lie group G2, it is possible to perform lattice simulations at finite density, while still retaining neutrons. Here, results of these lattice simulations are used to determine the mass-radius relation of a neutron star for this theory. The results show that phase changes express themselves in this relation. Also, the radius of the most massive neutron stars is found to vary very little, which would make radius determinations much simpler if this would also be true in QCD.

  6. Constraints on the mass-radius relation of the neutron star in 4U 1746-37/NGC 6441

    Science.gov (United States)

    Sztajno, M.; Fujimoto, M. Y.; Van Paradijs, J.; Vacca, W. D.; Lewin, W. H. G.

    1987-01-01

    An analysis of 12 hours of continuous EXOSAT observations of 4U 1746-37 in NGC 6441, obtained between September 9 and 10, 1985, puts constraints on its mass-radius relation. The spectral shape of the persistent X-ray flux is well fitted by a thermal bremsstrahlung spectrum, with a kT temperature varying between 7.5 and 9.8 keV, and an interstellar column density of about 2.8 x 10 to the 21st/sq cm. Two X-ray bursts noted during the observation are found to be type I, with radius expansion of the neutron star photosphere during their peaks. If the neutron star has a canonical mass of 1.4 solar masses, the observed burst fluxes must be reduced as a result of anisotropy of the burst by a factor of at least 1.3-2.2. The present results are consistent with the very soft and intermediately stiff equations of state.

  7. Upper Bounds on r-Mode Amplitudes from Observations of Low-Mass X-Ray Binary Neutron Stars

    Science.gov (United States)

    Mahmoodifar, Simin; Strohmayer, Tod

    2013-01-01

    We present upper limits on the amplitude of r-mode oscillations and gravitational-radiation-induced spin-down rates in low-mass X-ray binary neutron stars, under the assumption that the quiescent neutron star luminosity is powered by dissipation from a steady-state r-mode. For masses <2M solar mass we find dimensionless r-mode amplitudes in the range from about 1×10(exp-8) to 1.5×10(exp-6). For the accreting millisecond X-ray pulsar sources with known quiescent spin-down rates, these limits suggest that approx. less than 1% of the observed rate can be due to an unstable r-mode. Interestingly, the source with the highest amplitude limit, NGC 6440, could have an r-mode spin-down rate comparable to the observed, quiescent rate for SAX J1808-3658. Thus, quiescent spin-down measurements for this source would be particularly interesting. For all sources considered here, our amplitude limits suggest that gravitational wave signals are likely too weak for detection with Advanced LIGO. Our highest mass model (2.21M solar mass) can support enhanced, direct Urca neutrino emission in the core and thus can have higher r-mode amplitudes. Indeed, the inferred r-mode spin-down rates at these higher amplitudes are inconsistent with the observed spin-down rates for some of the sources, such as IGR J00291+5934 and XTE J1751-305. In the absence of other significant sources of internal heat, these results could be used to place an upper limit on the masses of these sources if they were made of hadronic matter, or alternatively it could be used to probe the existence of exotic matter in them if their masses were known.

  8. Beyond the Horizon Distance: LIGO-Virgo can Boost Gravitational Wave Detection Rates by Exploiting the Mass Distribution of Neutron Stars

    CERN Document Server

    Bartos, Imre

    2015-01-01

    The masses of neutron stars in neutron star binaries are observed to fall in a narrow mass range around $\\sim 1.33$ M$_{\\odot}$. We explore the advantage of focusing on this region of the parameter space in gravitational wave searches. We find that an all-sky (externally triggered) search with optimally reduced template bank is expected to detect $14\\%$ ($61\\%$) more binary mergers than without the reduction. A reduced template bank can also represent significant improvement in technical cost. We also develop a more detailed search method using binary mass distribution, and find similar sensitivity increase to that due to the reduced template bank.

  9. Neutrino Processes in Neutron Stars

    Directory of Open Access Journals (Sweden)

    Kolomeitsev E.E.

    2010-10-01

    Full Text Available The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities. The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong

  10. Effects of the gravitational waves emission on the orbit of the binary neutron stars considering the mass variation.

    Science.gov (United States)

    Mabrouk, Zeinab; Rahoma, W. A.

    2016-07-01

    Gravitational waves which have been announced finally to be detected in February 11, 2016 are believed to be emitted from many sources and phenomena in the universe, the binary neutron stars systems specially the inspirals are one kind of them. In this paper we are going to calculate the effects of this emission on the elements of the elliptical orbits of such binary neutron stars before the onset of the mass exchange. We based our work on the Imshennik and Popov (1994) paper then we do some modifications. The main and important results that Imshennik and Popov get were the rate of change of the eccentricity e, the rate of change of the semi major axis a, and the monotonic dependence between them a=a(e). Finally they concluded the smallness of the final eccentricity which make the orbits to be near-circular due to the emission of the gravitational waves. Our modification is to consider the masses of the two binary stars to be varied using the famous Eddington-Jeams law, then we expand them around the time t using Taylor expansion. we do this variation first for one mass with the constancy of the second one, then we let both mosses to vary together. We start the algorithm from the beginning substituting with our new series of masses in the two main equations, the average rate of change of the total energy of the system (dE/dt) , and the average rate of change of the angular momentum (dJ/dt). This modification leads to new expressions of the previous mentioned rate of changes of the orbital elements obtained by Imshennik and Popov, some of them we obtained and still working in the rest.

  11. Probing neutron star physics using accreting neutron stars

    Directory of Open Access Journals (Sweden)

    Patruno A.

    2010-10-01

    Full Text Available We give an obervational overview of the accreting neutron stars systems as probes of neutron star physics. In particular we focus on the results obtained from the periodic timing of accreting millisecond X-ray pulsars in outburst and from the measurement of X-ray spectra of accreting neutron stars during quiescence. In the first part of this overview we show that the X-ray pulses are contaminated by a large amount of noise of uncertain origin, and that all these neutron stars do not show evidence of spin variations during the outburst. We present also some recent developments on the presence of intermittency in three accreting millisecond X-ray pulsars and investigate the reason why only a small number of accreting neutron stars show X-ray pulsations and why none of these pulsars shows sub-millisecond spin periods. In the second part of the overview we introduce the observational technique that allows the study of neutron star cooling in accreting systems as probes of neutron star internal composition and equation of state. We explain the phenomenon of the deep crustal heating and present some recent developments on several quasi persistent X-ray sources where a cooling neutron star has been observed.

  12. The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel

    CERN Document Server

    Quaintrell, H; Ash, T D C; Roche, P; Willems, B; Bedding, T R; Baldry, I K; Fender, R P

    2003-01-01

    We report new radial velocity observations of GP Vel/HD77581, the optical companion to the eclipsing X-ray pulsar Vela X-1. Using data spanning more than two complete orbits of the system, we detect evidence for tidally induced non-radial oscillations on the surface of GP Vel, apparent as peaks in the power spectrum of the residuals to the radial velocity curve fit. By removing the effect of these oscillations (to first order) and binning the radial velocities, we have determined the semi-amplitude of the radial velocity curve of GP Vel to be K_o=22.6+/-1.5 km/s. Given the accurately measured semi-amplitude of the pulsar's orbit, the mass ratio of the system is 0.081+/-0.005. We are able to set upper and lower limits on the masses of the component stars as follows. Assuming GP Vel fills its Roche lobe then the inclination angle of the system, i=70.1+/-2.6 deg. In this case we obtain the masses of the two stars as M_x=2.27 +/-0.17 M_sun for the neutron star and M_o=27.9+/-1.3 M_sun for GP Vel. Conversely, assu...

  13. On Magnetized Neutron Stars

    CERN Document Server

    Lopes, Luiz L

    2014-01-01

    In this work we review the formalism normally used in the literature about the effects of density-dependent magnetic fields on the properties of neutron stars, expose some ambiguities that arise and propose a way to solve the related problem. Our approach uses a different prescription for the calculation of the pressure based on the chaotic field formalism for the stress tensor and also a different way of introducing a variable magnetic field, which depends on the energy density rather than on the baryonic density.

  14. Keplerian frequency of uniformly rotating neutron stars and quark stars

    CERN Document Server

    Haensel, P; Bejger, M; Lattimer, J M

    2009-01-01

    We calculate Keplerian (mass shedding) configurations of rigidly rotating neutron stars and quark stars with crusts. We check the validity of empirical formula for Keplerian frequency, f_K, proposed by Lattimer & Prakash, f_K(M)=C (M/M_sun)^1/2 (R/10km)^-3/2, where M is the (gravitational) mass of Keplerian configuration, R is the (circumferential) radius of the non-rotating configuration of the same gravitational mass, and C = 1.04 kHz. Numerical calculations are performed using precise 2-D codes based on the multi-domain spectral methods. We use a representative set of equations of state (EOSs) of neutron stars and quark stars. We show that the empirical formula for f_K(M) holds within a few percent for neutron stars with realistic EOSs, provided 0.5 M_sun < M < 0.9 M_max,stat, where M_max,stat is the maximum allowable mass of non-rotating neutron stars for an EOS, and C=C_NS=1.08 kHz. Similar precision is obtained for quark stars with 0.5 M_sun < M < 0.9 M_max,stat. For maximal crust masses...

  15. Physics of Neutron Star Crusts

    Directory of Open Access Journals (Sweden)

    Chamel Nicolas

    2008-12-01

    Full Text Available The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

  16. Axion emission from neutron stars

    Science.gov (United States)

    Iwamoto, N.

    1984-01-01

    It is shown that axion emission from neutron stars is the dominant energy-loss mechanism for a range of values of the Peccei-Quinn symmetry-breaking scale (F) not excluded by previous constraints. This gives the possibility of obtaining a better bound on F from measurements of surface temperature of neutron stars.

  17. Magnetic Fields of Neutron Stars

    Indian Academy of Sciences (India)

    Sushan Konar

    2017-09-01

    This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.

  18. Probing neutron stars with gravitational waves

    CERN Document Server

    Owen, Benjamin J

    2009-01-01

    Within the next decade gravitational-wave (GW) observations by Advanced LIGO in the United States, Advanced Virgo and GEO HF in Europe, and possibly other ground-based instruments will provide unprecedented opportunities to look directly into the dense interiors of neutron stars which are opaque to all forms of electromagnetic (EM) radiation. The 10-10000 Hz frequency band available to these ground-based interferometers is inhabited by many neutron star mode frequencies, spin frequencies, and inverse dynamical timescales. GWs can provide information on bulk properties of neutron stars (masses, radii, locations...) as well as microphysics of their substance (crystalline structure, viscosity, composition...), some of which is difficult or impossible to obtain by EM observations alone. The former will tell us about the astrophysics of neutron stars, and the latter will illuminate fundamental issues in nuclear and particle physics and the physics of extremely condensed matter. Although GW searches can be done "bl...

  19. Grand Unification in Neutron Stars

    CERN Document Server

    Kaspi, Victoria M

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to `isolated neutron stars,' from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-ray Observatory, in celebration of its tenth anniversary. Finally, I describe the current status of efforts at physical `grand unification' of this wealth of observational phenomena, and comment on possibilities for Chandra's next decade in this field.

  20. Grand unification of neutron stars.

    Science.gov (United States)

    Kaspi, Victoria M

    2010-04-20

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical "grand unification" of this wealth of observational phenomena, and comment on possibilities for Chandra's next decade in this field.

  1. Grand unification of neutron stars

    Science.gov (United States)

    Kaspi, Victoria M.

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205

  2. NuSTAR observations of the neutron star low-mass X-ray binary GX 349+2 throughout its Z-track

    Science.gov (United States)

    Coughenour, Benjamin; Cackett, Edward; Miller, Jon M.

    2017-08-01

    Although the brightest class of neutron star low mass X-ray binaries, known as Z-sources, have been well studied, their behavior is not fully understood. In particular, what causes these sources to trace out the characteristic Z-shaped pattern on color-color or hardness-intensity diagrams is not well known. By studying the physical properties of the different spectral states of these sources, we may better understand such variability. With that goal in mind, we present a recent NuSTAR observation of the Z-source GX 349+2, which spans approximately 2 days, and covers all its spectral states. By creating a hardness-intensity diagram we were able to extract four spectra and trace the change in spectral parameters throughout the Z track. GX 349+2 shows a strong, broad Fe Kα line in all states. Through modeling of the reflection spectrum and Fe Kα line we find that in most states the inner disk radius is consistent with remaining unchanged, and being close to the neutron star. However, during the brightest flaring branch the inner disk radius from reflection is not well constrained.

  3. Limiting rotational period of neutron stars

    Science.gov (United States)

    Glendenning, Norman K.

    1992-11-01

    We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.

  4. Systematic Uncertainties in the Spectroscopic Measurements of Neutron-Star Masses and Radii from Thermonuclear X-ray Bursts. II. Eddington Limit

    OpenAIRE

    Guver, Tolga; Ozel, Feryal; Psaltis, Dimitrios

    2011-01-01

    Time resolved X-ray spectroscopy of thermonuclear bursts observed from low mass X-ray binaries offer a unique tool to measure neutron star masses and radii. In this paper, we continue our systematic analysis of all the X-ray bursts observed with RXTE from X-ray binaries. We determine the events which show clear evidence for photospheric radius expansion and measure the Eddington limits for these accreting neutron stars using the bolometric fluxes attained at the touchdown moments of each X-ra...

  5. Novel modelling of ultracompact X-ray binary evolution - stable mass transfer from white dwarfs to neutron stars

    Science.gov (United States)

    Sengar, Rahul; Tauris, Thomas M.; Langer, Norbert; Istrate, Alina G.

    2017-09-01

    Tight binaries of helium white dwarfs (He WDs) orbiting millisecond pulsars (MSPs) will eventually `merge' due to gravitational damping of the orbit. The outcome has been predicted to be the production of long-lived ultracompact X-ray binaries (UCXBs), in which the WD transfers material to the accreting neutron star (NS). Here we present complete numerical computations, for the first time, of such stable mass transfer from a He WD to a NS. We have calculated a number of complete binary stellar evolution tracks, starting from pre-low-mass X-ray binary systems, and evolved these to detached MSP+WD systems and further on to UCXBs. The minimum orbital period is found to be as short as 5.6 min. We followed the subsequent widening of the systems until the donor stars become planets with a mass of ˜0.005 M⊙ after roughly a Hubble time. Our models are able to explain the properties of observed UCXBs with high helium abundances and we can identify these sources on the ascending or descending branch in a diagram displaying mass-transfer rate versus orbital period.

  6. Pycnonuclear burning and accreting neutron stars

    CERN Document Server

    Yakovlev, D G

    2002-01-01

    We outline the phenomenon of deep crustal heating in transiently accreting neutron stars. It is produced by nuclear transformations (mostly, by pycnonuclear reactions) in accreted matter while this matter sinks to densities rho > 10^{10} g/cc under the weight of freshly accreted material. We consider then thermal states of transiently accreting neutron stars (with mean mass accretion rates \\dot{M}=(10^{-14}-10^{-9}) M_\\odot/yr) determined by deep crustal heating. In a simplified fashion we study how the thermal flux emergent from such stars depends on the properties of superdense matter in stellar interiors. We analyze the most important regulators of the thermal flux: strong superfluidity in the cores of low-mass stars and fast neutrino emission (in nucleon, pion-condensed, kaon-condensed, or quark phases of dense matter) in the cores of high-mass stars. We compare the results with observations of soft X-ray transients in quiescent states.

  7. From nuclear structure to neutron stars

    CERN Document Server

    Gandolfi, Stefano

    2013-01-01

    Recent progress in quantum Monte Carlo with modern nucleon-nucleon interactions have enabled the successful description of properties of light nuclei and neutron-rich matter. As a demonstration, we show that the agreement between theoretical calculations of the charge form factor of 12C and the experimental data is excellent. Applying similar methods to isospin-asymmetric systems allows one to describe neutrons confined in an external potential and homogeneous neutron-rich matter. Of particular interest is the nuclear symmetry energy, the energy cost of creating an isospin asymmetry. Combining these advances with recent observations of neutron star masses and radii gives insight into the equation of state of neutron-rich matter near and above the saturation density. In particular, neutron star radius measurements constrain the derivative of the symmetry energy.

  8. Hysteresis in the spectral states of the neutron star low-mass X-ray binary EXO 1745-248

    CERN Document Server

    Mukherjee, Arunava

    2011-01-01

    We study the low-frequency timing properties and the spectral state evolution of the transient neutron star low-mass X-ray binary EXO 1745-248 using the entire Rossi X-ray Timing Explorer Proportional Counter Array data. We tentatively conclude that EXO 1745-248 is an atoll source, and report the discovery of a ~ 0.45 Hz low-frequency quasi-periodic oscillation and ~ 10 Hz peaked noises. If it is an atoll, this source is unusual because (1) instead of a `C'-like curve, it traced a clear overall clockwise hysteresis curve in each of the colour-colour diagram and the hardness-intensity diagram; and (2) the source took at least 2.5 months to trace the softer banana state, as opposed to a few hours to a day, which is typical for an atoll source. The shape of the hysteresis track was intermediate between the characteristic `q'-like curves of several black hole systems and `C'-like curves of atolls, implying that EXO 1745-248 is an important source for the unification of the black hole and neutron star accretion pr...

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

    CERN Document Server

    van de Voort, Freeke; Hopkins, Philip F; Keres, Dusan; Faucher-Giguere, Claude-Andre

    2014-01-01

    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 sta...

  10. Constraints on neutron-star theories from nearby neutron star observations

    CERN Document Server

    Neuhäuser, Ralph; Tetzlaff, Nina; Hohle, Markus M; Eisenbeiss, Thomas

    2011-01-01

    We try to constrain the nuclear Equation-of-State (EoS) and supernova ejecta models by observations of young neutron stars in our galactic neighbourhood. There are seven thermally emitting isolated neutron stars known from X-ray and optical observations, the so-called Magnificent Seven, which are young (few Myrs), nearby (few hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that - by observing their surface - we can determine their luminosity, distance, and temperature, hence, their radius. We also see the possibility to determine their current neutron star masses and the masses of their progenitor stars by studying their origin. It is even feasible to find the neutron star which was born in the supernova, from which those Fe60 atoms were ejected, which were recently found in the Earth crust.

  11. Antikaon condensation in neutron stars

    CERN Document Server

    Pal, S; Greiner, W

    2000-01-01

    We investigate the condensation of charged K sup - meson and neutral anti-K sup 0 meson in dense neutron star matter. Calculations are performed in relativistic mean field models in which both the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson exchange. It is found that anti-K sup 0 condensation is quite sensitive to the antikaon optical potential and depends more strongly on the nucleonic equation of state. For moderate values of antikaon potential and a rather stiff equation of state, a significant region of maximum mass star will contain anti-K sup 0 meson. The critical density of anti-K sup 0 condensation is always higher than that of K sup - condensation. With the appearance of K sup - and anti-K sup 0 condensates, pairs of p-K sup - and n-Kbar sup 0 are produced with equal proportion leading to a perfectly symmetric matter of nucleons and antikaons in neutron stars. Along with K sup - condensate, anti-K sup 0 condensate makes the equation of state much softer resulting in smaller...

  12. Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust

    CERN Document Server

    Meisel, Z; Ahn, S; Bazin, D; Brown, B A; Browne, J; Carpino, J F; Chung, H; Cole, A L; Cyburt, R H; Estradé, A; Famiano, M; Gade, A; Langer, C; Matoš, M; Mittig, W; Montes, F; Morrissey, D J; Pereira, J; Schatz, H; Schatz, J; Scott, M; Shapira, D; Smith, K; Stevens, J; Tan, W; Tarasov, O; Towers, S; Wimmer, K; Winkelbauer, J R; Yurkon, J; Zegers, R G T

    2015-01-01

    We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)(+0 -54) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass-chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We found that, in contrast to prev...

  13. Axion Cooling of Neutron Stars

    CERN Document Server

    Sedrakian, Armen

    2015-01-01

    Cooling simulations of neutron stars and their comparison with the data from thermally emitting X-ray sources puts constraints on the properties of axions, and by extension of any light pseudo-scalar dark matter particles, whose existence has been postulated to solve the strong-CP problem of QCD. We incorporate the axion emission by pair-breaking and formation processes by $S$- and $P$-wave nucleonic condensates in a benchmark code for cooling simulations as well as provide fit formulae for the rates of these processes. Axion cooling of neutron stars has been simulated for 24 models covering the mass range 1 to 1.8 solar masses, featuring non-accreted iron and accreted light element envelopes, and a range of nucleon-axion coupling. The models are based on an equation state predicting conservative physics of superdense nuclear matter that does not allow for onset of fast cooling processes induced by phase transitions to non-nucleonic forms of matter or high proton concentration. The cooling tracks in the tempe...

  14. Super-Massive Neutron Stars

    CERN Document Server

    Freire, Paulo C C

    2007-01-01

    We present here the results of Arecibo timing of PSR B1516+02B, a 7.95-ms pulsar in a binary system with a ~0.17 solar mass companion and an orbital period of 6.85 days located in the globular cluster M5. The eccentricity of the orbit (e = 0.14) has allowed a measurement of the rate of advance of periastron: (0.0136 +/- 0.0007) degrees per year. It is very likely that the periastron advance is due to the effects of general relativity; the total mass of the binary system is (2.14 +/-0.16) solar masses. The small measured mass function implies, in a statistical sense, that a very large fraction of this total mass is contained in the pulsar: (1.94+0.17 -0.19) solar masses (1-sigma); there is a 5% probability that the mass of this object is below 1.59 solar masses. With the possible exception of PSR J1748-2021B, this is the largest neutron star mass measured to date. When combined with similar measurements made previously for Terzan 5 I and J, we can exclude, in a statistical sense, the ``soft'' equations of stat...

  15. Observational signatures of neutron stars in low-mass X-ray binaries climbing a stability peak

    CERN Document Server

    Kantor, Elena; Chugunov, Andrey

    2015-01-01

    In the recent papers by Gusakov, Chugunov, and Kantor (2014) a new scenario describing evolution of rapidly rotating neutron stars in low-mass X-ray binaries was proposed. The scenario accounts for a resonant interaction of normal r modes with superfluid inertial modes at some specific internal stellar temperatures ("resonance temperatures"). This interaction results in an enhanced damping of r mode and appearance of the "stability peaks" in the temperature -- spin frequency plane, which split the r-mode instability window in the vicinity of the resonance temperatures. The scenario suggests that the hot and rapidly rotating NSs spend most of their life climbing up these peaks and, in particular, are observed there at the moment. We analyze in detail possible observational signatures of this suggestion. In particular, we show that these objects may exhibit `anti-glitches' -- sudden frequency jumps on a time scale of hours-months.

  16. Holographic Quark Matter and Neutron Stars.

    Science.gov (United States)

    Hoyos, Carlos; Jokela, Niko; Rodríguez Fernández, David; Vuorinen, Aleksi

    2016-07-15

    We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars.

  17. Massive neutron stars and their implications

    Indian Academy of Sciences (India)

    T K Jha; Keshab C Panda

    2014-05-01

    Recent observations of high mass pulsar PSRJ1614-2230 has raised serious debate over the possible role of exotics in the dense core of neutron stars. The precise measurement of mass of the pulsar may play a very important role in limiting equation of state (EoS) of dense matter and its composition. Indirectly, it may also shape our understanding of the nucleon–hyperon or hyperon–hyperon interactions which is not well known. Within the framework of an effective chiral model, we compute models of neutron stars and analyse the hyperon composition in them. Further related implications are also discussed.

  18. Observational constraints on quarks in neutron stars

    CERN Document Server

    Nana, P; Nana, Pan; Xiaoping, Zheng

    2006-01-01

    We estimate the constraints of observational mass and redshift on the properties of equations of state for quarks in the compact stars. We discuss two scenarios: strange stars and hybrid stars. We construct the equations of state utilizing MIT bag model taking medium effect into account for quark matter and relativistic mean field theory for hadron matter. We find that quark may exist in strange stars and the interior of neutron stars, and only these quark matters with stiff equations of state could be consistent with both constraints. The bag constant is main one parameter that affects the mass strongly for strange stars and only the intermediate coupling constant may be the best choice for compatibility with observational constraints in hybrid stars.

  19. Theory of neutron star magnetospheres

    CERN Document Server

    Curtis Michel, F

    1990-01-01

    An incomparable reference for astrophysicists studying pulsars and other kinds of neutron stars, "Theory of Neutron Star Magnetospheres" sums up two decades of astrophysical research. It provides in one volume the most important findings to date on this topic, essential to astrophysicists faced with a huge and widely scattered literature. F. Curtis Michel, who was among the first theorists to propose a neutron star model for radio pulsars, analyzes competing models of pulsars, radio emission models, winds and jets from pulsars, pulsating X-ray sources, gamma-ray burst sources, and other neutron-star driven phenomena. Although the book places primary emphasis on theoretical essentials, it also provides a considerable introduction to the observational data and its organization. Michel emphasizes the problems and uncertainties that have arisen in the research as well as the considerable progress that has been made to date.

  20. Neutron Star News and Puzzles

    CERN Document Server

    Prakash, Madappa

    2014-01-01

    Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. In this article, I give a brief account of some of the many ways in which Gerry shaped my research. Recent and on-going research on neutron stars in which the group built from scratch by Gerry at Stony Brook has made significant strides are reviewed. Selected puzzles about neutron stars that remain to be solved are noted.

  1. Neutron star news and puzzles

    Science.gov (United States)

    Prakash, Madappa

    2014-08-01

    Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. This article gives a brief account of some of the many ways in which Gerry shaped my research. Focus is placed on the significant strides on neutron star research made by the group at Stony Brook, which Gerry built from scratch. Selected puzzles about neutron stars that remain to be solved are noted.

  2. OPTICAL SPECTROSCOPY OF THE HIGH-MASS γ-RAY BINARY 1FGL J1018.6−5856: A PROBABLE NEUTRON STAR PRIMARY

    Energy Technology Data Exchange (ETDEWEB)

    Strader, Jay; Chomiuk, Laura; Peacock, Mark [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Salinas, Ricardo [Gemini Observatory, Casilla 603, La Serena (Chile)

    2015-11-10

    We present medium-resolution optical spectroscopy with the SOAR telescope of the O star secondary of the high-mass γ-ray binary 1FGL J1018.6–5856 to help determine whether the primary is a neutron star or black hole. We find that the secondary has a low radial velocity semi-amplitude of 11–12 km s{sup −1}, with consistent values obtained for H and He absorption lines. This low value strongly favors a neutron star primary: while a black hole cannot be excluded if the system is close to face on, such inclinations are disallowed by the observed rotation of the secondary. We also find the high-energy (X-ray and γ-ray) flux maxima occur when the star is behind the compact object along our line of sight, inconsistent with a simple model of anisotropic inverse Compton scattering for the γ-ray photons.

  3. Rapidly rotating neutron star progenitors

    Science.gov (United States)

    Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.

    2016-12-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In this paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE (Binary Star Evolution) population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 yr. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1-1 per cent of the total core collapses, depending on the common envelope efficiency.

  4. Effects of △-Isobars on Neutron Stars

    Institute of Scientific and Technical Information of China (English)

    Jorge L.S. Lino; CHEN Yan-Jun; GUO Hua

    2008-01-01

    We have investigated the possibility of the presence of the deltas in neutron star matter and their effects on neutron stars. △-meson couplings of the theoretical predictions are only restricted in a region where the deltas can be present and even a first-order phase transition may take place, making the EOS softer and the maximum mass of neutron stars smaller. The presence of the deltas leads to the rapid decrease of neutrino mean free paths.

  5. Binary Neutron Star Mergers

    Directory of Open Access Journals (Sweden)

    Joshua A. Faber

    2012-07-01

    Full Text Available We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.

  6. The direct cooling tail method for X-ray burst analysis to constrain neutron star masses and radii

    CERN Document Server

    Suleimanov, Valery F; Nättilä, Joonas; Kajava, Jari J E; Revnivtsev, Mikhail G; Werner, Klaus

    2016-01-01

    Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X-ray binaries provides a unique opportunity to study NS parameters, because of the high fluxes, large luminosity variations and the related changes in the spectral properties. The standard cooling tail method uses hot NS atmosphere models to convert the observed spectral evolution during cooling stages of X-ray bursts to the Eddington flux F_Edd and the stellar angular size \\Omega. These are then translated to the constraints on the NS mass M and radius R. Here we present the improved, direct cooling tail method that generalises the standard approach. First, we adjust the cooling tail method to account for the bolometric correction to the flux. Then, we fit the observed dependence of the blackbody normalization on flux with a theoretical model directly on the M-R plane by interpolating theoretical dependences to a gi...

  7. The direct cooling tail method for X-ray burst analysis to constrain neutron star masses and radii

    Science.gov (United States)

    Suleimanov, Valery F.; Poutanen, Juri; Nättilä, Joonas; Kajava, Jari J. E.; Revnivtsev, Mikhail G.; Werner, Klaus

    2017-04-01

    Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X-ray binaries provides a unique opportunity to study NS parameters, because of the high fluxes, large luminosity variations and the related changes in the spectral properties. The standard cooling tail method uses hot NS atmosphere models to convert the observed spectral evolution during cooling stages of X-ray bursts to the Eddington flux FEdd and the stellar angular size Ω. These are then translated to the constraints on the NS mass M and radius R. Here we present the improved, direct cooling tail method that generalizes the standard approach. First, we adjust the cooling tail method to account for the bolometric correction to the flux. Then, we fit the observed dependence of the blackbody normalization on flux with a theoretical model directly on the M-R plane by interpolating theoretical dependences to a given gravity, hence ensuring only weakly informative priors for M and R instead of FEdd and Ω. The direct cooling method is demonstrated using a photospheric radius expansion burst from SAX J1810.8-2609, which has happened when the system was in the hard state. Comparing to the standard cooling tail method, the confidence regions are shifted by 1σ towards larger radii, giving R = 11.5-13.0 km at M = 1.3-1.8 M⊙ for this NS.

  8. Relativistic Iron Line Emission from the Neutron Star Low-mass X-ray Binary 4U 1636-536

    OpenAIRE

    Pandel, Dirk; Kaaret, Philip; Corbel, Stephane

    2008-01-01

    We present an analysis of XMM-Newton and RXTE data from three observations of the neutron star LMXB 4U 1636-536. The X-ray spectra show clear evidence of a broad, asymmetric iron emission line extending over the energy range 4-9 keV. The line profile is consistent with relativistically broadened Fe K-alpha emission from the inner accretion disk. The Fe K-alpha line in 4U 1636-536 is considerably broader than the asymmetric iron lines recently found in other neutron star LMXBs, which indicates...

  9. Mass-capture rate by the neutron star in be/x-ray Binaries

    OpenAIRE

    Okazaki, A. T.; Hayasaki, K.

    2004-01-01

    Estudiamos la interacci on entre el disco de estrellas Be y la estrella de neutrones en binarias Be/rayos X mediante simulaciones en tres dimensiones SPH. Encontramos que el truncamiento resonante del disco de la estrella Be opera bien excepto para sistemas con excentricidad orbital extremadamente alta o grandes angulos de desalineaci on entre el disco Be y el plano orbital. Debido al truncamiento, la tasa de captura de masa por la estrella de neutrones es sensible tanto a la exc...

  10. Proton Fraction in Neutron Stars

    Institute of Scientific and Technical Information of China (English)

    张丰收; 陈列文

    2001-01-01

    The proton fraction in β-stable neutron stars is investigated within the framework of the Skyrme-Hartree-Fock theory using the extended Skyrme effective interaction for the first time. The calculated results show that the proton fraction disappears at high density, which implies that the pure neutron matter may exist in the interior of neutron stars. The incompressibility of the nuclear equation-of-state is shown to be more important to determine the proton fraction. Meanwhile, it is indicated that the addition of muons in neutron stars will change the proton fraction. It is also found that the higher-order terms of the nuclear symmetry energy have obvious effects on the proton fraction and the parabolic law of the nuclear symmetry energy is not enough to determine the proton fraction.

  11. Rapidly rotating neutron star progenitors

    Science.gov (United States)

    Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.

    2016-08-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1 - 1% of the total core collapses, depending on the common envelope efficiency.

  12. The Nuclear Physics of Neutron Stars

    CERN Document Server

    Piekarewicz, J

    2013-01-01

    We explore the unique and fascinating structure of neutron stars. Although neutron stars are of interest in many areas of Physics, our aim is to provide an intellectual bridge between Nuclear Physics and Astrophysics. We argue against the naive perception of a neutron star as a uniform assembly of neutrons packed to enormous densities. Rather, by focusing on the many exotic phases that are speculated to exist in a neutron star, we show how the reality is different and far more interesting.

  13. Exploring fundamental physics with neutron stars

    CERN Document Server

    Pizzochero, Pierre M

    2016-01-01

    In this lecture, we give a first introduction to neutron stars, based on fundamental physical principles. After outlining their outstanding macroscopic properties, as obtained from observations, we infer the extreme conditions of matter in their interiors. We then describe two crucial physical phenomena which characterize compact stars, namely the gravitational stability of strongly degenerate matter and the neutronization of nuclear matter with increasing density, and explain how the formation and properties of neutron stars are a direct consequence of the extreme compression of matter under strong gravity. Finally, we describe how multi-wavelength observations of different external macroscopic features (e.g. maximum mass, surface temperature, pulsar glitches) can give invaluable information about the exotic internal microscopic scenario: super-dense, isospin-asymmetric, superfluid, bulk hadronic matter (probably deconfined in the most central regions) which can be found nowhere else in the Universe. Indeed,...

  14. Neutron stars as probes of extreme energy density matter

    Indian Academy of Sciences (India)

    Madappa Prakash

    2015-05-01

    Neutron stars have long been regarded as extraterrestrial laboratories from which we can learn about extreme energy density matter at low temperatures. In this article, some of the recent advances made in astrophysical observations and related theory are highlighted. Although the focus is on the much needed information on masses and radii of several individual neutron stars, the need for additional knowledge about the many facets of neutron stars is stressed. The extent to which quark matter can be present in neutron stars is summarized with emphasis on the requirement of non-perturbative treatments. Some longstanding and new questions, answers to which will advance our current status of knowledge, are posed.

  15. Impact of phase transition from neutrons to hyperons in neutron star properties

    Science.gov (United States)

    Alrizal, Sulaksono, A.

    2017-07-01

    We revisit the impact of phase transition from neutrons to hyperons in the properties of neutron star using BSP parameter set of relativistic mean field (RMF) model. Similar to the work reported in Reference [1], the significance of the phase transition is observed from the impact gσ∗Λ/gσN variation on the corresponding neutron stars equation of state and mass versus radius relation. The impact of anisotropic pressure on equation of state and mass versus radius relation of neutron stars is also investigated. It is found that equation of state of neutron stars is very sensitive to gσ∗Λ/gσN coupling constant variation. However, different to the result of Reference [1], we do not obtain hyperon stars with very small radii R˜ 8 km. We do not also find significant effect of anisotropic pressure to change the behavior of neutron star properties due to phase transition.

  16. Old and new neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Ruderman, M.

    1984-09-01

    The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10/sup 38/s/sup -1/ of 10/sup 12/ eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10/sup 8/ old dead pulsars in the Galaxy are the most probable source for the isotropically distributed ..gamma..-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables.

  17. 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

  18. Magnetic fields of neutron stars

    CERN Document Server

    Reisenegger, Andreas

    2013-01-01

    Neutron stars contain the strongest magnetic fields known in the Universe. In this paper, I discuss briefly how these magnetic fields are inferred from observations, as well as the evidence for their time-evolution. I show how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes. I propose a scenario in which a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) is established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, becau...

  19. Dense hadronic matter in neutron stars

    CERN Document Server

    Pagliara, Giuseppe; Lavagno, Andrea; Pigato, Daniele

    2014-01-01

    The existence of stars with masses up to $2 M_{\\odot}$ and the hints of the existence of stars with radii smaller than $\\sim 11$ km seem to require, at the same time, a stiff and a soft hadronic equation of state at large densities. We argue that these two apparently contradicting constraints are actually an indication of the existence of two families of compact stars: hadronic stars which could be very compact and quark stars which could be very massive. In this respect, a crucial role is played, in the hadronic equation of state, by the delta isobars whose early appearance shifts to large densities the formation of hyperons. We also discuss how recent experimental information on the symmetry energy of nuclear matter at saturation indicate, indirectly, an early appearance of delta isobars in neutron star matter.

  20. Neutron stars structure in the context of massive gravity

    Science.gov (United States)

    Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

    2017-07-01

    Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

  1. A cold neutron star in the transient low-mass X-ray binary HETE J1900.1-2455 after 10 years of active accretion

    CERN Document Server

    Degenaar, N; Reynolds, M T; Wijnands, R; Page, D

    2016-01-01

    The neutron star low-mass X-ray binary and intermittent millisecond X-ray pulsar HETE J1900.1-2455 returned to quiescence in late 2015, after a prolonged accretion outburst of ~10 yr. Using a Chandra observation taken ~180 d into quiescence we detect the source at a luminosity of ~4.5E31 (D/4.7 kpc)^2 erg/s (0.5-10 keV). The X-ray spectrum can be described by a neutron star atmosphere model with a temperature of ~54 eV for an observer at infinity. We perform thermal evolution calculations based on the 2016 quiescent data and a <98 eV temperature upper limit inferred from a Swift observation taken during an unusually brief (<2 weeks) quiescent episode in 2007. We find no evidence in the present data that the thermal properties of the crust, such as the heating rate and thermal conductivity, are different than those of non-pulsating neutron stars. Finding this neutron star so cold after its long outburst imposes interesting constraints on the heat capacity of the stellar core; these become even stronger i...

  2. Potential cooling of an accretion-heated neutron star crust in the low-mass X-ray binary 1RXS J180408.9-342058

    CERN Document Server

    Parikh, Aastha S; Degenaar, Nathalie; Ootes, Laura S; Page, Dany; Altamirano, Diego; Cackett, Edward M; Deller, Adam T; Gusinskaia, Nina; Hessels, Jason W T; Homan, Jeroen; Linares, Manuel; Miller, Jon M; Miller-Jones, James C A

    2016-01-01

    We have monitored the transient neutron star low-mass X-ray binary 1RXS J180408.9-342058 in quiescence after the end of its ~4.5 month outburst in 2015. The source has been observed 34 times using Swift and once using XMM-Newton in order to study the cooling of an accretion heated neutron star crust. During both the Swift and the XMM-Newton observations the X-ray spectra were dominated by a thermal component. The thermal evolution showed a gradual decay in the X-ray luminosity from ~18x10^32 to ~4x10^32 (D/5.8 kpc)^2 erg s^{-1} and the inferred neutron star surface temperature (for an observer at infinity) decreased from ~100 to ~72 eV between ~8 to ~379 days after the end of outburst. This can be interpreted as cooling of a neutron star crust that had been heated due to accretion during the preceding outburst. Modeling the observed temperature curve with the thermal evolution code NSCool indicated that the source required ~1.9 MeV per accreted nucleon of shallow heating in addition to the standard deep crust...

  3. A search for iron emission lines in the Chandra X-ray spectra of neutron star low-mass X-ray binaries

    CERN Document Server

    Cackett, E M; Homan, J; Van der Klis, M; Lewin, W H G; Méndez, M; Raymond, J; Steeghs, D; Wijnands, R

    2008-01-01

    While iron emission lines are well studied in black hole systems, both in X-ray binaries and Active Galactic Nuclei, there has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent observations with Suzaku and XMM-Newton have revealed broad asymmetric iron line profiles in 4 neutron star LMXBs, confirming an inner disk origin for these lines in neutron star systems. Here, we present a search for iron lines in 6 neutron star LMXBs. For each object we have simultaneous Chandra and RXTE observations at 2 separate epochs, allowing for both a high resolution spectrum, as well as broadband spectral coverage. Out of the six objects in the survey, we only find significant iron lines in two of the objects, GX 17+2 and GX 349+2. However, we cannot rule out that there are weak, broad lines present in the other sources. The equivalent width of the line in GX 17+2 is consistent between the 2 epochs, while in GX 349+2 the line equivalent width increases by a factor of ~3 betwe...

  4. A cold neutron star in the transient low-mass X-ray binary HETE J1900.1-2455 after 10 yr of active accretion

    Science.gov (United States)

    Degenaar, N.; Ootes, L. S.; Reynolds, M. T.; Wijnands, R.; Page, D.

    2017-02-01

    The neutron star low-mass X-ray binary and intermittent millisecond X-ray pulsar HETE J1900.1-2455 returned to quiescence in late 2015, after a prolonged accretion outburst of ≃10 yr. Using a Chandra observation taken ≃180 d into quiescence, we detect the source at a luminosity of ≃4.5 × 1031 (D/4.7 kpc)2 erg s-1 (0.5-10 keV). The X-ray spectrum can be described by a neutron star atmosphere model with a temperature of ≃54 eV for an observer at infinity. We perform thermal evolution calculations based on the 2016 quiescent data and a ≲98 eV temperature upper limit inferred from a Swift observation taken during an unusually brief (≲2 weeks) quiescent episode in 2007. We find no evidence in the present data that the thermal properties of the crust, such as the heating rate and thermal conductivity, are different than those of non-pulsating neutron stars. Finding this neutron star so cold after its long outburst imposes interesting constraints on the heat capacity of the stellar core; these become even stronger if further cooling were to occur.

  5. Neutron Stars in the Laboratory

    CERN Document Server

    Graber, Vanessa; Hogg, Michael

    2016-01-01

    Neutron stars are astrophysical laboratories of many extremes of physics. Their rich phenomenology provides insights into the state and composition of matter at densities which cannot be reached in terrestrial experiments. Since the core of a mature neutron star is expected to be dominated by superfluid and superconducting components, observations also probe the dynamics of large-scale quantum condensates. The testing and understanding of the relevant theory tends to focus on the interface between the astrophysics phenomenology and nuclear physics. The connections with low-temperature experiments tend to be ignored. However, there has been dramatic progress in understanding laboratory condensates (from the different phases of superfluid helium to the entire range of superconductors and cold atom condensates). In this review, we provide an overview of these developments, compare and contrast the mathematical descriptions of laboratory condensates and neutron stars and summarise the current experimental state-o...

  6. Neutron stars are gold mines

    Science.gov (United States)

    Lattimer, James M.

    Neutron stars are not only mines for clues to dense matter physics but may also be the auspicious sources of half of all nuclei heavier than A = 60 in the universe, including the auric isotopes. Although the cold dense matter above the nuclear saturation density cannot be directly explored in the laboratory, gilded constraints on the properties of matter from 1 to 10 times higher density can now be panned from neutron star observations. We show how upcoming observations, such as gravitational wave from mergers, precision timing of pulsars, neutrinos from neutron star birth and X-rays from bursts and thermal emissions, will provide the bullion from which further advances can be smelted.

  7. Superfluidity and Superconductivity in Neutron Stars

    Indian Academy of Sciences (India)

    N. Chamel

    2017-09-01

    Neutron stars, the compact stellar remnants of core-collapse supernova explosions, are unique cosmic laboratories for exploring novel phases of matter under extreme conditions. In particular, the occurrence of superfluidity and superconductivity in neutron stars will be briefly reviewed.

  8. ULXs: Neutron Stars vs Black Holes

    CERN Document Server

    King, Andrew

    2016-01-01

    We consider ultraluminous X-ray sources (ULXs) where the accretor is a neutron star rather than a black hole. We show that the recently-discovered example (M82 X-2) fits naturally into the simple picture of ULXs as beamed X-ray sources fed at super-Eddington rates, provided that its magnetic field is weaker ($\\simeq 10^{11}{\\rm G}$) than a new-born X-ray pulsar, as expected if there has been mass gain. Continuing accretion is likely to weaken the field to the point that pulsing stops, and make the system indistinguishable from a ULX containing a black hole. Accordingly we suggest that a significant fraction of all ULXs may actually contain neutron star accretors rather than black holes, reflecting the neutron-star fraction among their X-ray binary progenitors. We emphasize that neutron-star ULXs are likely to have {\\it higher} apparent luminosities than black hole ULXs for a given mass transfer rate, as their tighter beaming outweighs their lower Eddington luminosities. This further increases the likely propo...

  9. Jet quenching in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    Science.gov (United States)

    Gusinskaia, N. V.; Deller, A. T.; Hessels, J. W. T.; Degenaar, N.; Miller-Jones, J. C. A.; Wijnands, R.; Parikh, A. S.; Russell, T. D.; Altamirano, D.

    2017-09-01

    We present quasi-simultaneous radio (VLA) and X-ray ($Swift$) observations of the neutron star low-mass X-ray binary (NS-LMXB) 1RXS J180408.9$-$342058 (J1804) during its 2015 outburst. We found that the radio jet of J1804 was bright ($232 \\pm 4 \\mu$Jy at $10$ GHz) during the initial hard X-ray state, before being quenched by more than an order of magnitude during the soft X-ray state ($19 \\pm 4 \\mu$Jy). The source then was undetected in radio ( 0.7$ (where $L_R \\propto L_X^{\\beta}$). Few other sources have been studied in this faint regime, but a steep track is inconsistent with the suggested behaviour for the recently identified class of transitional millisecond pulsars. J1804 also shows fainter radio emission at $L_X < 10^{35}$ erg s$^{-1}$ than what is typically observed for accreting millisecond pulsars. This suggests that J1804 is likely not an accreting X-ray or transitional millisecond pulsar.

  10. The Magneto Hydro Dynamical Model of KHz Quasi Periodic Oscillations in Neutron Star Low Mass X-ray Binaries (II)

    CERN Document Server

    Shi, Chang-Sheng; Li, Xiang-Dong

    2014-01-01

    We study the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries (LMXBs) with a new magnetohydrodynamics (MHD) model, in which the compressed magnetosphere is considered. The previous MHD model (Shi \\& Li 2009) is re-examined and the relation between the frequencies of the kHz QPOs and the accretion rate in LMXBs is obtained. Our result agrees with the observations of six sources (4U 0614+09, 4U 1636--53, 4U 1608--52, 4U 1915--15, 4U 1728--34, XTE 1807--294) with measured spins. In this model the kHz QPOs originate from the MHD waves in the compressed magnetosphere. The single kHz QPOs and twin kHz QPOs are produced in two different parts of the accretion disk and the boundary is close to the corotation radius. The lower QPO frequency in a frequency-accretion rate diagram is cut off at low accretion rate and the twin kHz QPOs encounter a top ceiling at high accretion rate due to the restriction of innermost stable circular orbit.

  11. The Electromagnetic Spectrum of Neutron Stars

    CERN Document Server

    Baykal, Altan; Inam, Sitki C; Grebenev, Sergei

    2005-01-01

    Neutron stars hold a central place in astrophysics, not only because they are made up of the most extreme states of the condensed matter, but also because they are, along with white dwarfs and black holes, one of the stable configurations that stars reach at the end of stellar evolution. Neutron stars posses the highest rotation rates and strongest magnetic fields among all stars. They radiate prolifically, in high energy electromagnetic radiation and in the radio band. This book is devoted to the selected lectures presented in the 6th NATO-ASI series entitled "The Electromagnetic Spectrum of Neutron Stars" in Marmaris, Turkey, on 7-18 June 2004. This ASI is devoted to the spectral properties of neutron stars. Spectral observations of neutron stars help us to understand the magnetospheric emission processes of isolated radio pulsars and the emission processes of accreting neutron stars. This volume includes spectral information from the neutron stars in broadest sense, namely neutrino and gravitational radiat...

  12. Testing the relativistic precession model using low frequency and kHz quasi-periodic oscillations in neutron star low mass X-ray binaries with known spin

    CERN Document Server

    van Doesburgh, Marieke

    2016-01-01

    We analyze all available RXTE data on a sample of 13 low mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model (RPM) that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency $\

  13. On the compactness of neutron stars

    CERN Document Server

    Chen, Wei-Chia

    2015-01-01

    Recent progress in the determination of both masses and radii of neutron stars are starting to place stringent constraints on the dense matter equation of state. In particular, new theoretical developments together with improved statistical tools seem to favor stellar radii that are significantly smaller than those predicted by models using purely nucleonic equations of state. Given that the underlying equation of state must also account for the observation of $2M_{\\odot}$ neutron stars, theoretical approaches to the study of the dense matter equation of state are facing serious challenges. In response to this challenge, we compute in a model-independent way the underlying equation of state associated with an assumed mass-radius template similar to the "common radius" assumption used in recent studies. Once such a mass-radius template is adopted, the equation of state follows directly from the implementation of Lindblom's algorithm; assumptions on the nature or composition of the dense stellar core are not re...

  14. Neutron Stars: Laboratories for Fundamental Physics Under Extreme Astrophysical Conditions

    Science.gov (United States)

    Bandyopadhyay, Debades

    2017-09-01

    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 experiments. It is observed that equations of state involving strangeness degrees of freedom such as hyperons and Bose-Einstein condensates are compatible with 2{M}_{solar} neutron stars. The role of hyperons is explored on the evolution and stability of the protoneutron star in the context of SN1987A. Moment of inertia, mass and radius which are direct probes of neutron star interior are computed and their observational consequences are discussed. We continue our study on the dense matter under strong magnetic fields and its application to magnetoelastic oscillations of neutron stars.

  15. From neutron stars to quark stars in mimetic gravity

    Science.gov (United States)

    Astashenok, Artyom V.; Odintsov, Sergei D.

    2016-09-01

    Realistic models of neutron and quark stars in the framework of mimetic gravity with a Lagrange multiplier constraint are presented. We discuss the effect of a mimetic scalar aiming to describe dark matter on the mass-radius relation and the moment of inertia for slowly rotating relativistic stars. The mass-radius relation and moment of inertia depend on the value of the mimetic scalar in the center of the star. This fact leads to the ambiguity in the mass-radius relation for a given equation of state. Such ambiguity allows us to explain some observational facts better than in standard general relativity. The case of mimetic potential V (ϕ )˜A eC ϕ2 is considered in detail. The relative deviation of the maximal moment of inertia is approximately twice as large as the relative deviation of the maximal stellar mass. We also briefly discuss the mimetic f (R ) gravity. In the case of f (R )=R +a R2 mimetic gravity, it is expected that the increase of maximal mass and maximal moment of inertia due to the mimetic scalar becomes much stronger with bigger parameter a . The influence of the scalar field in mimetic gravity can lead to the possible existence of extreme neutron stars with large masses.

  16. Observations and modeling of the companions of short period binary millisecond pulsars: evidence for high-mass neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, Joshua; Halpern, Jules [Department of Astronomy, Columbia University, Mail Code 5246, 550 West 120th Street, New York, NY 10027 (United States)

    2014-10-01

    We present observations of fields containing eight recently discovered binary millisecond pulsars using the telescopes at MDM Observatory. Optical counterparts to four of these systems are detected, one of which, PSR J2214+3000, is a novel detection. Additionally, we present the fully phase-resolved B, V, and R light curves of the optical counterparts to two objects, PSR J1810+1744 and PSR J2215+5135 for which we employ model fitting using the eclipsing light curve (ELC) model of Orosz and Hauschildt to measure the unknown system parameters. For PSR J1810+1744, we find that the system parameters cannot be fit even assuming that 100% of the spin-down luminosity of the pulsar is irradiating the secondary, and so radial velocity measurements of this object will be required for the complete solution. However, PSR J2215+5135 exhibits light curves that are extremely well constrained using the ELC model and we find that the mass of the neutron star is constrained by these and the radio observations to be M {sub NS} > 1.75 M {sub ☉} at the 3σ level. We also find a discrepancy between the model temperature and the measured colors of this object, which we interpret as possible evidence for an additional high-temperature source such as a quiescent disk. Given this and the fact that PSR J2215+5135 contains a relatively high mass companion (M {sub c} > 0.1 M {sub ☉}), we propose that similar to the binary pulsar systems PSR J1023+0038 and IGR J18245–2452, the pulsar may transition between accretion- and rotation-powered modes.

  17. Neutrino emission in neutron stars

    NARCIS (Netherlands)

    van Dalen, ENE; Dieperink, AEL; Tjon, JA

    Neutrino emissivities in a neutron star are computed for the neutrino bremsstrahlung process. In the first part, the electroweak nucleon-nucleon bremsstrahlung is calculated in free space in terms of an on-shell T matrix using a generalized low-energy theorem. In the second part, the emissivities

  18. On the Origin of Broad Iron Lines in Neutron Star Low-mass X-ray Binaries

    CERN Document Server

    Chiang, Chia-Ying; Miller, Jon M; Barret, Didier; Fabian, Andy C; D'Ai, Antonino; Parker, Michael L; Bhattacharyya, Sudip; Burderi, Luciano; Di Salvo, Tiziana; Egron, Elise; Homan, Jeroen; Iaria, Rosario; Lin, Dacheng; Miller, M Coleman

    2015-01-01

    Broad Fe K emission lines have been widely observed in the X-ray spectra of black hole systems, and in neutron star systems as well. The intrinsically narrow Fe K fluorescent line is generally believed to be part of the reflection spectrum originating in an illuminated accretion disk, and broadened by strong relativistic effects. However, the nature of the lines in neutron star LMXBs has been under debate. We therefore obtained the longest, high-resolution X-ray spectrum of a neutron star LMXB to date with a 300 ks Chandra HETGS observation of Serpens X-1. The observation was taken under the "continuous clocking" mode and thus free of photon pile-up effects. We carry out a systematic analysis and find that the blurred reflection model fits the Fe line of Serpens X-1 significantly better than a broad Gaussian component does, implying that the relativistic reflection scenario is much preferred. Chandra HETGS also provides highest spectral resolution view of the Fe K region and we find no strong evidence for add...

  19. Determination of hadron-quark phase transition line from lattice QCD and two-solar-mass neutron star observations

    CERN Document Server

    Sugano, Junpei; Yahiro, Masahiro

    2016-01-01

    We aim at drawing the hadron-quark phase transition line in the QCD phase diagram by using the two phase model (TPM) in which the entanglement Polyakov-loop extended Nambu--Jona-Lasinio (EPNJL) model with vector-type four-quark interaction is used for the quark phase and the relativistic mean field (RMF) model is for the hadron phase. Reasonable TPM is constructed by using lattice QCD data and neutron star observations as reliable constraints. For the EPNJL model, we determine the strength of vector-type four-quark interaction at zero quark chemical potential from lattice QCD data on quark number density normalized by its Stefan-Boltzmann limit. For the hadron phase, we consider three RMF models, NL3, TM1 and model proposed by Maruyama, Tatsumi, Endo and Chiba (MTEC). We find that MTEC is most consistent with the neutron star observations and TM1 is the second best. Assuming that the hadron-quark phase transition occurs in the core of neutron star, we explore the density-dependence of vector-type four-quark i...

  20. Do hyperons exist in the interior of neutron stars?

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Debarati [Universite Paris Diderot, LUTH, Observatoire de Paris, CNRS, Meudon (France); Laboratoire de Physique Corpusculaire, ENSICAEN, Caen Cedex (France); Vidana, Isaac [University of Coimbra, CFisUC, Department of Physics, Coimbra (Portugal)

    2016-02-15

    In this work we review the role of hyperons on the properties of neutron and proto-neutron stars. In particular, we revise the so-called ''hyperon puzzle'', go over some of the solutions proposed to tackle it, and discuss the implications that the recent measurements of unusually high neutron star masses have on our present knowledge of hypernuclear physics. We re-examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability. (orig.)

  1. The mass, radius, distance and cooling of the neutron star in EXO 0748-676 in quiescence with XMM-Newton

    Science.gov (United States)

    Cheng, Zheng; Mendez, Mariano; Costantini, Elisa; Diaz Trigo, Maria

    2016-07-01

    We present the spectral analysis of four XMM-Newton observations of the neutron-star low-mass X-ray binary EXO 0748-676 in quiescence, taken between 2009 and 2013. We fit the spectra with an absorbed neutron-star atmosphere model, without the need for a high-energy (power-law) component, with a 95 per cent confidence upper limit of 1 per cent to the contribution of the power law to the total flux of the source in the 0.2-10.0 keV band. We find a significant emission line at around 0.5 keV in the spectra of the three CCD cameras on board XMM-Newton of all four observations; the line, which we tentatively identify as Lyα emission from NVII, is moderately broad, σ ≈ 0.17 keV, and contributes ˜10-14 per cent of the total flux in the 0.2-10 keV band. The temperature of the neutron star in EXO 0748-676 has decreased significantly compared to the previous XMM-Newton observation, with the cooling curve being consistent with either an exponential decay plus a constant, a power law or a broken power-law. We fitted the spectra with a neutron-star atmosphere model that takes into account the observed peak flux of photospheric radius expansion (PRE) bursts to constrain the neutron-star mass, radius and distance self-consistently. Using this model we carried out MCMC simulations assuming a uniform prior for the inclination angle of the system (which accounts for anisotropy in the emission at the peak of the bursts) and for the hydrogen fraction of the fuel during the PRE bursts. We find that M _{ns} = 1.87 ^{+0.69}_{-0.32} M⊙, R_{ns} = 8.5^{+3.2}_{-1.3} km and D = 5.4^{+2.4}_{-1.2} kpc (99% confidence level), which is inconsistent with quark-bearing equations of state for this neutron star.

  2. NSCool: Neutron star cooling code

    Science.gov (United States)

    Page, Dany

    2016-09-01

    NSCool is a 1D (i.e., spherically symmetric) neutron star cooling code written in Fortran 77. The package also contains a series of EOSs (equation of state) to build stars, a series of pre-built stars, and a TOV (Tolman- Oppenheimer-Volkoff) integrator to build stars from an EOS. It can also handle “strange stars” that have a huge density discontinuity between the quark matter and the covering thin baryonic crust. NSCool solves the heat transport and energy balance equations in whole GR, resulting in a time sequence of temperature profiles (and, in particular, a Teff - age curve). Several heating processes are included, and more can easily be incorporated. In particular it can evolve a star undergoing accretion with the resulting deep crustal heating, under a steady or time-variable accretion rate. NSCool is robust, very fast, and highly modular, making it easy to add new subroutines for new processes.

  3. Probing thermonuclear burning on accreting neutron stars

    Science.gov (United States)

    Keek, L.

    2008-12-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating

  4. A gravitational wave afterglow in binary neutron star mergers

    CERN Document Server

    Doneva, Daniela D; Pnigouras, Pantelis

    2015-01-01

    We study in detail the f-mode secular instability for rapidly rotating neutron stars, putting emphasis on supermassive models which do not have a stable nonrotating counterpart. Such neutron stars are thought to be the generic outcome of the merger of two standard mass neutron stars. In addition we take into account the effects of strong magnetic field and r-mode instability, that can drain a substantial amount of angular momentum. We find that the gravitational wave signal emitted by supramassive neutron stars can reach above the Advance LIGO sensitivity at distance of about 20Mpc and the detectability is substantially enhanced for the Einstein Telescope. The event rate will be of the same order as the merging rates, while the analysis of the signal will carry information for the equation of state of the post-merging neutron stars and the strength of the magnetic fields.

  5. Gravitational waves from surface inhomogeneities of neutron stars

    Science.gov (United States)

    Konar, Sushan; Mukherjee, Dipanjan; Bhattacharya, Dipankar; Sarkar, Prakash

    2016-11-01

    Surface asymmetries of accreting neutron stars are investigated for their mass quadrupole moment content. Though the amplitude of the gravitational waves from such asymmetries seems to be beyond the limit of detectability of the present generation of detectors, it appears that rapidly rotating neutron stars with strong magnetic fields residing in high-mass x-ray binaries would be worth considering for a targeted search for continuous gravitational waves with the next generation of instruments.

  6. Energy Density Functional for Nuclei and Neutron Stars

    Energy Technology Data Exchange (ETDEWEB)

    Erler, J. [UTK/ORNL/German Cancer Research Center-Heidelberg; Horowitz, C. J. [UTK/ORNL/Indiana University; Nazarewicz, Witold [UTK/ORNL/University of Warsaw; Rafalski, M. [UTK/ORNL; Reinhard, P.-G. [Universitat Erlangen, Germany

    2013-01-01

    Background: Recent observational data on neutron star masses and radii provide stringent constraints on the equation of state of neutron rich matter [ Annu. Rev. Nucl. Part. Sci. 62 485 (2012)]. Purpose: We aim to develop a nuclear energy density functional that can be simultaneously applied to finite nuclei and neutron stars. Methods: We use the self-consistent nuclear density functional theory (DFT) with Skyrme energy density functionals and covariance analysis to assess correlations between observables for finite nuclei and neutron stars. In a first step two energy functionals a high density energy functional giving reasonable neutron properties, and a low density functional fitted to nuclear properties are matched. In a second step, we optimize a new functional using exactly the same protocol as in earlier studies pertaining to nuclei but now including neutron star data. This allows direct comparisons of performance of the new functional relative to the standard one. Results: The new functional TOV-min yields results for nuclear bulk properties (energy, rms radius, diffraction radius, and surface thickness) that are of the same quality as those obtained with the established Skyrme functionals, including SV-min. When comparing SV-min and TOV-min, isoscalar nuclear matter indicators vary slightly while isovector properties are changed considerably. We discuss neutron skins, dipole polarizability, separation energies of the heaviest elements, and proton and neutron drip lines. We confirm a correlation between the neutron skin of 208Pb and the neutron star radius. Conclusions: We demonstrate that standard energy density functionals optimized to nuclear data do not carry information on the expected maximum neutron star mass, and that predictions can only be made within an extremely broad uncertainty band. For atomic nuclei, the new functional TOV-min performs at least as well as the standard nuclear functionals, but it also reproduces expected neutron star data

  7. Model Atmospheres for X-ray Bursting Neutron Stars

    CERN Document Server

    Medin, Zach; Calder, Alan C; Fontes, Christopher J; Fryer, Chris L; Hungerford, Aimee L

    2016-01-01

    The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where X-ray bursts occur. Observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.

  8. (K)0 Condensation in Hyperonic Neutron Star Matter

    Institute of Scientific and Technical Information of China (English)

    DING Wen-Bo; LIU Guang-Zhou; ZHU Ming-Feng; YU Zi; ZHAO En-Guang

    2008-01-01

    In the framework of the relativistic mean field theory,we investigate (K)0 condensation along with Kˉcondensation occur well in the core of the maximum mass stars for relatively shallow optical potentials of (K) in the range of-100 MeV~-160 MeV.With the increasing optical potential of (K),the critical densities of (K) decrease and the species of baryons appearing in neutron stars become fewer.The main role of (K)0 condensation is to make the abundances of particles become identical leading to isospin saturated symmetric matter including antikaons,state,which leads to a large reduction in the maximum masses of neutron stars.In the core of massive neutron stars,neutron star matter including rich particle species,such as antikaons,nucleons and hyperons,may exist.

  9. Non-identical neutron star twins

    Energy Technology Data Exchange (ETDEWEB)

    Glendenning, Norman K.; Kettner, Christiane

    1998-07-01

    The work of J. A. Wheeler in the mid 1960's showed that forsmooth equations of state no stable stellar configurations with centraldensities above that corresponding to the limiting mass of 'neutronstars' (in the generic sense) were stable against acoustical vibrationalmodes. A perturbation would cause any such star to collapse to a blackhole or explode. Accordingly, there has been no reason to expect that astable degenerate family of stars with higher density than the knownwhite dwarfs and neutron stars might exist. We have found a class ofexceptions corresponding to certain equations of state that describe afirst order phase transition. We discuss how such a higher density familyof stars could be formed in nature, and how the promising new explorationof oscillations in the X-ray brightness of accreting neutron stars mightprovide a means of identifying them. Our proof of the possible existenceof a third family of degenerate stars is one of principle and rests ongeneral principles like causality, microstability of matter and GeneralRelativity.

  10. Fab Four Neutron Stars

    CERN Document Server

    Maselli, Andrea; Minamitsuji, Masato; Berti, Emanuele

    2016-01-01

    Horndeski's theory of gravity is the most general scalar-tensor theory with a single scalar whose equations of motion contain at most second-order derivatives. A subsector of Horndeski's theory known as "Fab Four" gravity allows for dynamical self-tuning of the quantum vacuum energy, and therefore it has received particular attention in cosmology as a possible alternative to the $\\Lambda$CDM model. Here we study compact stars in Fab Four gravity, which includes as special cases general relativity ("George"), Einstein-dilaton-Gauss-Bonnet gravity ("Ringo"), theories with a nonminimal coupling with the Einstein tensor ("John") and theories involving the double-dual of the Riemann tensor ("Paul"). We generalize and extend previous results in theories of the John class and we show that there are no viable compact star solutions in theories of the Paul class.

  11. Hard-tail emission in the soft state of low-mass X-ray binaries and their relation to the neutron star magnetic field

    CERN Document Server

    Asai, Kazumi; Mastuoka, Masaru; Sugizaki, Mutsumi

    2016-01-01

    Average hard-tail X-ray emission in the soft state of nine bright Atoll low-mass X-ray binaries containing a neutron star (NS-LMXBs) are investigated by using the light curves of MAXI/GSC and Swift/BAT. Two sources (4U 1820$-$30 and 4U 1735$-$44) exhibit large hardness ratio (15--50 keV$/$2--10 keV: {\\it HR} $>$ 0.1), while the other sources distribute at {\\it HR} $\\ltsim$ 0.1. In either case, {\\it HR} does not depend on the 2--10 keV luminosity. Therefore the difference of {\\it HR} is due to the 15--50 keV luminosity, which is Comptonized emission. The Compton cloud is assumed to be around the neutron star. The size of the Compton cloud would affect the value of {\\it HR}. Although the magnetic field of NS-LMXB is weak, we could expect a larger Alfv\\'{e}n radius than the innermost stable circular orbit or the neutron star radius in some sources. In such cases, the accretion inflow is stopped at the Alfv\\'{e}n radius and would create relatively large Compton cloud. It would result in the observed larger Compto...

  12. Hard-tail emission in the soft state of low-mass X-ray binaries and their relation to the neutron star magnetic field

    Science.gov (United States)

    Asai, Kazumi; Mihara, Tatehiro; Mastuoka, Masaru; Sugizaki, Mutsumi

    2016-08-01

    Average hard-tail X-ray emission in the soft state of nine bright Atoll low-mass X-ray binaries containing a neutron star (NS-LMXBs) are investigated by using the light curves of MAXI/GSC (Gas Slit Camera) and Swift/BAT (Burst Alert Telescope). Two sources (4U 1820-30 and 4U 1735-44) exhibit a large hardness ratio (15-50 keV/2-10 keV: HR >0.1), while the other sources distribute at HR ≲ 0.1. In either case, HR does not depend on the 2-10 keV luminosity. Therefore the difference of HR is due to the 15-50 keV luminosity, which is Comptonized emission. The Compton cloud is assumed to be around the neutron star. The size of the Compton cloud would affect the value of HR. Although the magnetic field of an NS-LMXB is weak, we could expect a larger Alfvén radius than the innermost stable circular orbit or the neutron star radius in some sources. In such cases, the accretion inflow is stopped at the Alfvén radius and would create a relatively large Compton cloud. This would result in the observed larger Comptonized emission. By attributing the difference of the size of Compton cloud to the Alfvén radius, we can estimate the magnetic fields of neutron stars. The obtained lower/upper limits are consistent with the previous results.

  13. Potential cooling of an accretion-heated neutron star crust in the low-mass X-ray binary 1RXS J180408.9-342058

    Science.gov (United States)

    Parikh, A. S.; Wijnands, R.; Degenaar, N.; Ootes, L. S.; Page, D.; Altamirano, D.; Cackett, E. M.; Deller, A. T.; Gusinskaia, N.; Hessels, J. W. T.; Homan, J.; Linares, M.; Miller, J. M.; Miller-Jones, J. C. A.

    2017-01-01

    We have monitored the transient neutron star low-mass X-ray binary 1RXS J180408.9-342058 in quiescence after its ˜4.5 month outburst in 2015. The source has been observed using Swift and XMM-Newton. Its X-ray spectra were dominated by a thermal component. The thermal evolution showed a gradual X-ray luminosity decay from ˜18 × 1032 to ˜4 × 1032 (D/5.8 kpc)2 erg s-1 between ˜8 to ˜379 days in quiescence and the inferred neutron star surface temperature (for an observer at infinity; using a neutron star atmosphere model) decreased from ˜100 to ˜71 eV. This can be interpreted as cooling of an accretion heated neutron star crust. Modeling the observed temperature curve (using NSCOOL) indicated that the source required ˜1.9 MeV per accreted nucleon of shallow heating in addition to the standard deep crustal heating to explain its thermal evolution. Alternatively, the decay could also be modelled without the presence of deep crustal heating, only having a shallow heat source (again ˜1.9 MeV per accreted nucleon was required). However, the XMM-Newton data statistically required an additional power-law component. This component contributed ˜30 per cent of the total unabsorbed flux in 0.5 - 10 keV energy range. The physical origin of this component is unknown. One possibility is that it arises from low-level accretion. The presence of this component in the spectrum complicates our cooling crust interpretation because it might indicate that the smooth luminosity and temperature decay curves we observed may not be due to crust cooling but due to some other process.

  14. Properties of Neutron Star Critical Collapses

    Science.gov (United States)

    Wan, Mew-Bing

    2010-01-01

    Critical phenomena in gravitational collapse opened a new mathematical vista into the theory of general relativity and may ultimately entail fundamental physical implication in observations. However, at present, the dynamics of critical phenomena in gravitational collapse scenarios are still largely unknown. My thesis seeks to understand the properties of the threshold in the solution space of the Einstein field equations between the black hole and neutron star phases, understand the properties of the neutron star critical solution and clarify the implication of these results on realistic astrophysical scenarios. We develop a new set of neutron star-like initial data to establish the universality of the neutron star critical solution and analyze the structure of neutron star and neutron star-like critical collapses via the study of the phase spaces. We also study the different time scales involved in the neutron star critical solution and analyze the properties of the critical index via comparisons between neutron star and neutron star-like initial data. Finally, we explore the boundary of the attraction basin of the neutron star critical solution and its transition to a known set of non-critical fixed points.

  15. Rapidly rotating neutron star progenitors

    CERN Document Server

    Postnov, K A; Kolesnikov, D A; Popov, S B; Porayko, N K

    2016-01-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, $\\tau_c$. The validity of this approach is checked by direct MESA calculations ...

  16. I-Love-Q: unexpected universal relations for neutron stars and quark stars.

    Science.gov (United States)

    Yagi, Kent; Yunes, Nicolás

    2013-07-26

    Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star's internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion.

  17. The EOS of neutron matter and the effect of $\\Lambda$ hyperons to neutron star structure

    CERN Document Server

    Gandolfi, Stefano

    2015-01-01

    The structure of neutron stars is determined by the equation of state of the matter inside the star, which relies on the knowledge of nuclear interactions. While radii of neutron stars mostly depend on the equation of state of neutron matter at nuclear densities, their maximum mass can be drastically affected by the appearance of hyperons at higher densities in the inner core of the star. We summarize recent quantum Monte Carlo results on the calculation of the equation of state of neutron matter at nuclear and higher densities. We report about the development of realistic hyperon-nucleon interactions based on the available experimental data for light- and medium-heavy hypernuclei and on the effect of $\\Lambda$ hyperons to the neutron star structure.

  18. Understanding Neutron Stars using Thermonuclear X-ray Bursts

    Science.gov (United States)

    Bhattacharyya, S.

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star = EOS model of high density cold matter in the neutron star cores. Extensive observation and analysis of the data from the rising portions of the bursts = modeling of burst oscillations and thermonuclear flame spreading. Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  19. Neutron Stars and Thermonuclear X-ray Bursts

    Science.gov (United States)

    Bhattacharyya, Sudip

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star approaching EOS model of high density cold matter in the neutron star cores. +k Extensive observation and analysis of the data from the rising portions of the bursts - modeling of burst oscillations and thermonuclear flame spreading. +k Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  20. Holographic quark matter and neutron stars

    CERN Document Server

    Hoyos, Carlos; Jokela, Niko; Vuorinen, Aleksi

    2016-01-01

    We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding Equation of State (EoS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first order phase transition at densities between two and seven times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EoSs, we find maximal stellar masses in the excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EoSs.

  1. Neutron Star Motion in the Disk Galaxy

    Institute of Scientific and Technical Information of China (English)

    WEI Ying-Chun; A.Taani; PAN Yuan-Yue; WANG Jing; CAI Yan; LIU Gao-Chao; LUO A-Li; ZHANG Hong-Bo; ZHAO Yong-Heng

    2010-01-01

    @@ The neutron star motions are based on the undisturbed finitely thick galactic disk gravitational potential model.Two initial conditions,I.e.the locations and velocities,are considered.The Monte Carlo method is employed to separate rich diversities of the orbits of neutron stars into several sorts.The Poincaré section has the potential to play an important role in the diagnosis of the neutron star motion.It has been observed that the increasing ratio of the motion range vertical to the galactic plane to that parallel to the galactic plane results in the irregularity of neutron star motion.

  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. Hybrid stars that masquerade as neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Mark Paris; Mark Alford; Matt Braby; Sanjay Reddy

    2004-11-01

    We show that a hybrid (nuclear + quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state, and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M{sub solar} for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.

  4. Slowly Rotating General Relativistic Superfluid Neutron Stars

    CERN Document Server

    Andersson, N

    2001-01-01

    We present a general formalism to treat slowly rotating general relativistic superfluid neutron stars. As a first approximation, their matter content can be described in terms of a two-fluid model, where one fluid is the neutron superfluid, which is believed to exist in the core and inner crust of mature neutron stars, and the other fluid represents a conglomerate of all other constituents (crust nuclei, protons, electrons, etc.). We obtain a system of equations, good to second-order in the rotational velocities, that determines the metric and the matter variables, irrespective of the equation of state for the two fluids. In particular, allowance is made for the so-called entrainment effect, whereby the momentum of one constituent (e.g. the neutrons) carries along part of the mass of the other constituent. As an illustration of the developed framework, we consider a simplified equation of state for which the two fluids are described by different polytropes. We determine numerically the effects of the two flui...

  5. Of Mountains and Molehills : Gravitational Waves from Neutron Stars

    CERN Document Server

    Konar, Sushan; Bhattacharya, Dipankar; Sarkar, Prakash

    2016-01-01

    Surface asymmetries of accreting neutron stars are investigated for their mass quadrupole moment content. Though the amplitude of the gravitational waves from such asymmetries seem to be beyond the limit of detectability of the present generation of detectors, it appears that rapidly rotating neutron stars with strong magnetic fields residing in HMXBs would be worth considering for targeted search for continuous gravitational waves with the next generation of instruments.

  6. Magnetic fields in Neutron Stars

    CERN Document Server

    Viganò, Daniele; Miralles, Juan A; Rea, Nanda

    2015-01-01

    Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

  7. Dynamics of Rotating, Magnetized Neutron Stars

    OpenAIRE

    Liebling, Steven L.

    2010-01-01

    Using a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions, the dynamics of magnetized, rigidly rotating neutron stars are studied. Beginning with fully consistent initial data constructed with Magstar, part of the Lorene project, we study the dynamics and stability of rotating, magnetized polytropic stars as models of neutron stars. Evolutions suggest that some of these rotating, magnetized stars may be minimally uns...

  8. The Dark Side of Neutron Stars

    DEFF Research Database (Denmark)

    Kouvaris, Christoforos

    2013-01-01

    We review severe constraints on asymmetric bosonic dark matter based on observations of old neutron stars. Under certain conditions, dark matter particles in the form of asymmetric bosonic WIMPs can be eectively trapped onto nearby neutron stars, where they can rapidly thermalize and concentrate...... in the core of the star. If some conditions are met, the WIMP population can collapse gravitationally and form a black hole that can eventually destroy the star. Based on the existence of old nearby neutron stars, we can exclude certain classes of dark matter candidates....

  9. The Dark Side of Neutron Stars

    Directory of Open Access Journals (Sweden)

    Chris Kouvaris

    2013-01-01

    Full Text Available We review severe constraints on asymmetric bosonic dark matter based on observations of old neutron stars. Under certain conditions, dark matter particles in the form of asymmetric bosonic WIMPs can be effectively trapped onto nearby neutron stars, where they can rapidly thermalize and concentrate in the core of the star. If some conditions are met, the WIMP population can collapse gravitationally and form a black hole that can eventually destroy the star. Based on the existence of old nearby neutron stars, we can exclude certain classes of dark matter candidates.

  10. Measuring the basic parameters of neutron stars using model atmospheres

    Energy Technology Data Exchange (ETDEWEB)

    Suleimanov, V.F. [Universitaet Tuebingen, Institut fuer Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Tuebingen (Germany); Kazan Federal University, Kazan (Russian Federation); Poutanen, J. [University of Turku, Tuorla Observatory, Department of Physics and Astronomy, Piikkioe (Finland); KTH Royal Institute of Technology and Stockholm University, Nordita, Stockholm (Sweden); Klochkov, D.; Werner, K. [Universitaet Tuebingen, Institut fuer Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Tuebingen (Germany)

    2016-02-15

    Model spectra of neutron star atmospheres are nowadays widely used to fit the observed thermal X-ray spectra of neutron stars. This fitting is the key element in the method of the neutron star radius determination. Here, we present the basic assumptions used for the neutron star atmosphere modeling as well as the main qualitative features of the stellar atmospheres leading to the deviations of the emergent model spectrum from blackbody. We describe the properties of two of our model atmosphere grids: i) pure carbon atmospheres for relatively cool neutron stars (1-4MK) and ii) hot atmospheres with Compton scattering taken into account. The results obtained by applying these grids to model the X-ray spectra of the central compact object in supernova remnant HESS 1731-347, and two X-ray bursting neutron stars in low-mass X-ray binaries, 4U 1724-307 and 4U 1608-52, are presented. Possible systematic uncertainties associated with the obtained neutron star radii are discussed. (orig.)

  11. Initial data for black hole-neutron star binaries, with rotating stars

    CERN Document Server

    Tacik, Nick; Pfeiffer, Harald P; Muhlberger, Curran; Kidder, Lawrence E; Scheel, Mark A; Szilagyi, Bela

    2016-01-01

    The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole--neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as $S_{\\rm BH}/M_{\\rm BH}^2=0.99$.

  12. Initial data for black hole–neutron star binaries, with rotating stars

    Science.gov (United States)

    Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Muhlberger, Curran; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla

    2016-11-01

    The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole–neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as {S}{BH}/{M}{BH}2=0.99.

  13. Light Curves for Rapidly-Rotating Neutron Stars

    CERN Document Server

    Cadeau, C; Leahy, D; Campbell, S S; Cadeau, Coire; Morsink, Sharon M.; Leahy, Denis; Campbell, Sheldon S.

    2006-01-01

    We present raytracing computations for light emitted from the surface of a rapidly-rotating neutron star in order to construct light curves for X-ray pulsars and bursters. These calculations are for realistic models of rapidly-rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect arising from rotation comes from the oblate shape of the rotating star. We find that approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, in most cases acceptable fits to the ratio M/R can be obtained with the spherical approximation.

  14. Observations of Type I Bursts from Neutron Stars

    CERN Document Server

    Swank, J H

    2000-01-01

    Observations of Type I X-ray bursts have long been taken as evidence that the sources are neutron stars. Black body models approximate the spectral data and imply a suddenly heated neutron star cooling over characteristic times of seconds to minutes. The phenomena are convincingly explained in terms of nuclear burning of accreted gas on neutron stars with low mass companion stars. Prospects are promising that detailed theory and data from RXTE and future missions will lead to better determinations of important physical parameters (neutron star mass and radius, composition of the accreting gas, distance of the source). Among the variety of bursts observed, there are probably representatives of different kinds of explosive burning. RXTE's discovery of a 2.5 ms persistent coherent period from one Type I burster has now linked bursters indisputably to the epitome of a neutron star, a fast spinning magnetic compact object. Oscillations in some bursts had already been thought to arise from the neutron stars' rotati...

  15. On the origin of the near-infrared emission from the neutron-star low-mass X-ray binary GX 9+1

    CERN Document Server

    Berg, Maureen van den

    2016-01-01

    We have determined an improved position for the luminous persistent neutron-star low-mass X-ray binary and atoll source GX 9+1 from archival Chandra X-ray Observatory data. The new position significantly differs from a previously published Chandra position for this source. Based on the revised X-ray position we have identified a new near-infrared (NIR) counterpart to GX 9+1 in Ks-band images obtained with the PANIC and FourStar cameras on the Magellan Baade Telescope. NIR spectra of this Ks=16.5+-0.1 mag star taken with the FIRE spectrograph on the Baade Telescope show a strong Br-gamma emission line, which is a clear signature that we discovered the true NIR counterpart to GX 9+1. The mass donor in GX 9+1 cannot be a late-type giant, as such a star would be brighter than the estimated absolute Ks magnitude of the NIR counterpart. The slope of the dereddened NIR spectrum is poorly constrained due to uncertainties in the column density N_H and NIR extinction. Considering the source's distance and X-ray luminos...

  16. Speed of sound bounds and neutron star structure

    CERN Document Server

    Moustakidis, Ch C; Margaritis, Ch; Lalazissis, G A

    2016-01-01

    The accurate determination of the maximum mass of the neutron stars is one of the most important tasks in Astrophysics. It is directly related with the identification of the black holes in the Universe, the production of neutron stars from the supernovae explosion and the Equation of State (EoS) of dense matter. However, not only the EoS is directly connected with neutron star masses, but also the speed of sound in dense matter is a crucial quantity which characterizes the stiffness of the EoS. The upper bound of the speed of sound imposes strong constraints on the maximum mass of neutron stars. However, this upper bound remains still an open issue. Recent observations, of binary neutron star systems, offer the possibility to measure with high accuracy both the mass and the tidal polarizability of the stars. We study possible effects of the upper bound of the speed of sound on the upper bound of the mass and the tidal polarizability. We conclude that this kind of measurements, combined with recent observation...

  17. Gravity Defied : From Potato Asteroids to Magnetised Neutron Stars 4. Neutron Stars (Dead Stars of the Second Kind)

    Indian Academy of Sciences (India)

    Sushan Konar

    2017-06-01

    A star burns its nuclear fuel and balances gravitation by thepressure of the heated gas, during its active lifetime. Afterthe exhaustion of the nuclear fuel, a low mass star findspeace as a ‘white dwarf’, where the pressure support againstgravitation is provided by Fermi-degenerate electrons. However,for massive stars, the gravitational squeeze becomes sosevere that in the final phase of evolution, the average densityapproximately equals the nuclear density. At such densities,most of the protons combine with electrons to convertthemselves into neutrons. A `neutron star', composed of suchneutron-rich material, is host to some fascinating physics arisingout of its amazingly compact state of matter (where a solarmass is packed inside a sphere of radius ∼ 10Km).

  18. Hydromagnetic Instabilities in Neutron Stars

    CERN Document Server

    Lasky, Paul D; Kokkotas, Kostas D; Glampedakis, Kostas

    2011-01-01

    We model the non-linear ideal magnetohydrodynamics of poloidal magnetic fields in neutron stars in general relativity assuming a polytropic equation of state. We identify familiar hydromagnetic modes, in particular the 'sausage/varicose' mode and 'kink' instability inherent to poloidal magnetic fields. The evolution is dominated by the kink instability, which causes a cataclysmic reconfiguration of the magnetic field. The system subsequently evolves to new, non-axisymmetric, quasi-equilibrium end-states. The existence of this branch of stable quasi-equilibria may have consequences for magnetar physics, including flare generation mechanisms and interpretations of quasi-periodic oscillations.

  19. Neutron Stars in Rastall Gravity

    CERN Document Server

    Oliveira, A M; Fabris, J C; Casarini, L

    2015-01-01

    We calculate static and spherically symmetric solutions for the Rastall modification of gravity to describe Neutron Stars (NS). The key feature of the Rastall gravity is the non-conservation of the energy-momentum tensor proportionally to the space-time curvature. Using realistic equations of state for the NS interior we place a bound on the non-GR behaviour of the Rastall theory which should be $\\lesssim 0.1\\%$ level. This work presents the more stringent contraints on the deviations of GR caused by the Rastall proposal.

  20. Relativistic calculations of coalescing binary neutron stars

    Indian Academy of Sciences (India)

    Joshua Faber; Phillippe Grandclément; Frederic Rasio

    2004-10-01

    We have designed and tested a new relativistic Lagrangian hydrodynamics code, which treats gravity in the conformally flat approximation to general relativity. We have tested the resulting code extensively, finding that it performs well for calculations of equilibrium single-star models, collapsing relativistic dust clouds, and quasi-circular orbits of equilibrium solutions. By adding a radiation reaction treatment, we compute the full evolution of a coalescing binary neutron star system. We find that the amount of mass ejected from the system, much less than a per cent, is greatly reduced by the inclusion of relativistic gravitation. The gravity wave energy spectrum shows a clear divergence away from the Newtonian point-mass form, consistent with the form derived from relativistic quasi-equilibrium fluid sequences.

  1. The outer crust of non-accreting cold neutron stars

    CERN Document Server

    Ruster, S B; Schaffner-Bielich, J; Ruster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jurgen

    2006-01-01

    The properties of the outer crust of non-accreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables updating in particular the classic work of Baym, Pethick and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 is used and a thorough comparison of many modern theoretical nuclear models, relativistic and non-relativistic ones, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared in order to check their differences concerning the neutron dripline, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the dripline in the outer crust of non-accreting cold neutron stars.

  2. Observational Constraints on Quark Matter in Neutron Stars

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We study the observational constraints of mass and redshift on the properties of the equation of state (EOS) for quark matter in compact stars based on the quasi-particle description. We discuss two scenarios: strange stars and hybrid stars. We construct the equations of state utilizing an extended MIT bag model taking the medium effect into account for quark matter and the relativistic mean field theory for hadron matter. We show that quark matter may exist in strange stars and in the interior of neutron stars. The bag constant is a key parameter that affects strongly the mass of strange stars. The medium effect can lead to the stiffer hybrid-star EOS approaching the pure hadronic EOS, due to the reduction of quark matter, and hence the existence of heavy hybrid stars. We find that a middle range coupling constant may be the best choice for the hybrid stars being compatible with the observational constraints.

  3. Cooling of neutron stars with diffusive envelopes

    CERN Document Server

    Beznogov, M V; Haensel, P; Yakovlev, D G; Zdunik, J L

    2016-01-01

    We study the effects of heat blanketing envelopes of neutron stars on their cooling. To this aim, we perform cooling simulations using newly constructed models of the envelopes composed of binary ion mixtures (H--He, He--C, C--Fe) varying the mass of lighter ions (H, He or C) in the envelope. The results are compared with those calculated using the standard models of the envelopes which contain the layers of lighter (accreted) elements (H, He and C) on top of the Fe layer, varying the mass of accreted elements. The main effect is that the chemical composition of the envelopes influences their thermal conductivity and, hence, thermal insulation of the star. For illustration, we apply these results to estimate the internal temperature of the Vela pulsar and to study the cooling of neutron stars of ages of 0.1 - 1 Myr at the photon cooling stage. The uncertainties of the cooling models associated with our poor knowledge of chemical composition of the heat insulating envelopes strongly complicate theoretical reco...

  4. Binary Neutron Star Mergers and Short Gamma-Ray Bursts: Effects of Magnetic Field Orientation, Equation of State, and Mass Ratio

    CERN Document Server

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

    2016-01-01

    We present fully GRMHD 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 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 found 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 BH. Such larger fields make it...

  5. Accretion Models for Young Neutron Stars

    OpenAIRE

    Alpar, M. Ali

    2003-01-01

    Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion models for explaining the properties of young neutron stars.

  6. From neutron stars to quark stars in mimetic gravity

    CERN Document Server

    Astashenok, A V

    2015-01-01

    Realistic models of neutron and quark stars in the framework of mimetic gravity with Lagrange multiplier constraint are presented. We discuss the effect of mimetic scalar aiming to describe dark matter on mass-radius relation and the moment of inertia for slowly rotating relativistic stars. The mass-radius relation and moment of inertia depend on the value of mimetic scalar in the center of star. This fact leads to the ambiguity in the mass-radius relation for a given equation of state. {Such ambiguity allows to explain some observational facts better than in standard General Relativity}. The case of two mimetic potentials namely $V(\\phi)\\sim A\\phi^{-2}$ and $V(\\phi)\\sim Ae^{B\\phi^{2}}$ is considered in detail. The relative deviation of maximal moment of inertia is approximately twice larger than the relative deviation of maximal stellar mass. We also briefly discuss the mimetic $f(R)$ gravity. In the case of $f(R)=R+aR^2$ mimetic gravity it is expected that increase of maximal mass and maximal moment of iner...

  7. Neutron stars as probes of extreme energy density matter

    CERN Document Server

    Prakash, Madappa

    2014-01-01

    Neutron stars have long been regarded as extra-terrestrial laboratories from which we can learn about extreme energy density matter at low temperatures. In this article, I highlight some of the recent advances made in astrophysical observations and related theory. Although the focus is on the much needed information on masses and radii of several individual neutron stars, the need for additional knowledge about the many facets of neutron stars is stressed. The extent to which quark matter can be present in neutron stars is summarized with emphasis on the requirement of non-perturbative treatments. Some longstanding and new questions, answers to which will advance our current status of knowledge, are posed.

  8. Magnetised Neutron Stars An Overview

    CERN Document Server

    Goyal, A

    2003-01-01

    In the presence of strong magnetic field reported to have been observed on the surface of some neutron stars and on what are called Magnetars, a host of physical phenomenon from the birth of a neutron star to free streaming neutrino cooling phase will be modified. In this review I will discuss the effect of magnetic field on the equation of state of high density nuclear matter by including the anomalous magnetic moment of the nucleons into consideration. I would then go over to discuss the neutrino interaction processes in strong as well as in weak magnetic fields. The neutrino processes are important in studying the propagation of neutrinos and in studying the energy loss, Their study is a prerequisite for the understanding of actual dynamics of supernova explosion and on the stabilization of radial pulsation modes through the effect on bulk viscosity. The anisotropy introduced in the neutrino emission and through the modification of the shape of the neutrino sphere may explain the observed pulsar kicks.

  9. Excited nuclei in neutron star crusts

    CERN Document Server

    Takibayev, Nurgali; Nasirova, Diana

    2012-01-01

    The paper considers the chains of successive electron capture reactions by nuclei of the iron group which take place in the crystal structures of neutron star envelopes. It is shown that as a result of such reactions the daughter nuclei in excited states accumulate within certain layers of neutron star crusts. The phonon model of interactions is proposed between the excited nuclei in the crystalline structure, as well as formation of highly excited nuclear states which emit neutrons and higher energy photons.

  10. How Loud Are Neutron Star Mergers?

    CERN Document Server

    Bernuzzi, Sebastiano; Ott, Christian D; Roberts, Luke F; Moesta, Philipp; Galeazzi, Filippo

    2015-01-01

    We investigate neutron star merger dynamics using fully general relativistic simulations of equal and unequal-mass binaries sampling the galactic population, and including neutrino cooling and three different temperature-dependent microphysical equations of state. We focus on the emission of energy and angular momentum in gravitational waves in the postmerger phase. Our results reveal that the emitted gravitational-wave energy in the early evolution of the formed hypermassive neutron star (HMNS) is about twice as large as the energy emitted over the entire inspiral history of the binary. The total radiated energy per binary mass is comparable or larger than that of nonspinning black hole mergers. About $0.8-2.5\\%$ of the binary mass-energy is emitted at kHz frequencies in the early HMNS evolution due to the strong nonaxisymmetric deformation of the HMNS. Our results also show that the dimensionless spin of black holes resulting from subsequent HMNS collapse are limited to $\\lesssim0.7-0.8$. This may significa...

  11. How loud are neutron star mergers?

    Science.gov (United States)

    Bernuzzi, Sebastiano; Radice, David; Ott, Christian D.; Roberts, Luke F.; Mösta, Philipp; Galeazzi, Filippo

    2016-07-01

    We present results from the first large parameter study of neutron star mergers using fully general relativistic simulations with finite-temperature microphysical equations of state and neutrino cooling. We consider equal and unequal-mass binaries drawn from the galactic population and simulate each binary with three different equations of state. Our focus is on the emission of energy and angular momentum in gravitational waves in the postmerger phase. We find that the emitted gravitational-wave energy in the first ˜10 ms of the life of the resulting hypermassive neutron star (HMNS) is about twice the energy emitted over the entire inspiral history of the binary. The total radiated energy per binary mass is comparable to or larger than that of nonspinning black hole inspiral-mergers. About 0.8-2.5% of the binary mass-energy is emitted at kHz frequencies in the early HMNS evolution. We find a clear dependence of the postmerger gravitational wave emission on binary configuration and equation of state and show that it can be encoded as a broad function of the binary tidal coupling constant κ2T. Our results also demonstrate that the dimensionless spin of black holes resulting from subsequent HMNS collapse are limited to ≲0.7 - 0.8 . This may significantly impact the neutrino pair annihilation mechanism for powering short gamma-ray bursts (sGRB).

  12. Neutron Star Crust and Molecular Dynamics Simulation

    CERN Document Server

    Horowitz, C J; Schneider, A; Berry, D K

    2011-01-01

    In this book chapter we review plasma crystals in the laboratory, in the interior of white dwarf stars, and in the crust of neutron stars. We describe a molecular dynamics formalism and show results for many neutron star crust properties including phase separation upon freezing, diffusion, breaking strain, shear viscosity and dynamics response of nuclear pasta. We end with a summary and discuss open questions and challenges for the future.

  13. Rotational properties of hypermassive neutron stars from binary mergers

    CERN Document Server

    Hanauske, Matthias; Bovard, Luke; Rezzolla, Luciano; Font, José A; Galeazzi, Filippo; Stöcker, Horst

    2016-01-01

    Determining the differential-rotation law of compact stellar objects produced in binary neutron stars mergers or core-collapse supernovae is an old problem in relativistic astrophysics. Addressing this problem is important because it impacts directly on the maximum mass these objects can attain and hence on the threshold to black-hole formation under realistic conditions. Using the results from a large number of numerical simulations in full general relativity of binary neutron star mergers described with various equations of state and masses, we study the rotational properties of the resulting hypermassive neutron stars. We find that the angular-velocity distribution shows only a modest dependence on the equation of state, thus exhibiting the traits of "quasi-universality" found in other aspects of compact stars, both isolated and in binary systems. The distributions are characterized by an almost uniformly rotating core and a quasi-Keplerian "disk". Such a configuration is significantly different from the $...

  14. 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

  15. Gravitational waves from rapidly rotating neutron stars

    CERN Document Server

    Haskell, Brynmor; D`Angelo, Caroline; Degenaar, Nathalie; Glampedakis, Kostas; Ho, Wynn C G; Lasky, Paul D; Melatos, Andrew; Oppenoorth, Manuel; Patruno, Alessandro; Priymak, Maxim

    2014-01-01

    Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed as an interesting source of gravitational waves. In this chapter we present estimates of the gravitational wave emission for various scenarios, given the (electromagnetically) observed characteristics of these systems. First of all we focus on the r-mode instability and show that a 'minimal' neutron star model (which does not incorporate exotica in the core, dynamically important magnetic fields or superfluid degrees of freedom), is not consistent with observations. We then present estimates of both thermally induced and magnetically sustained mountains in the crust. In general magnetic mountains are likely to be detectable only if the buried magnetic field of the star is of the order of $B\\approx 10^{12}$ G. In the thermal mountain case we find that gravitational wave emission from persistent systems may be detected by ground based interferometers. Finally we re-asses the idea that gravitational wave emission may be balancing the ac...

  16. Focused study of thermonuclear bursts on neutron stars

    DEFF Research Database (Denmark)

    Chenevez, Jérôme

    X-ray bursters are a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric...... detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X-ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of Simbol X may therefore make...

  17. Neutron star natal kicks and the long-term survival of star clusters

    CERN Document Server

    Contenta, Filippo; Heggie, Douglas C

    2015-01-01

    We investigate the dynamical evolution of a star cluster in an external tidal field by using N-body simulations, with focus on the effects of the presence or absence of neutron star natal velocity kicks.We show that, even if neutron stars typically represent less than 2% of the total bound mass of a star cluster, their primordial kinematic properties may affect the lifetime of the system by up to almost a factor of four. We interpret this result in the light of two known modes of star cluster dissolution, dominated by either early stellar evolution mass loss or two-body relaxation. The competition between these effects shapes the mass loss profile of star clusters, which may either dissolve abruptly ("jumping"), in the pre-core-collapse phase, or gradually ("skiing"), after having reached core collapse.

  18. Instability windows and evolution of rapidly rotating neutron stars

    CERN Document Server

    Gusakov, Mikhail E; Kantor, Elena M

    2013-01-01

    We consider an instability of rapidly rotating neutron stars in low-mass X-ray binaries (LMXBs) with respect to excitation of r-modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. We demonstrate that neutron stars with high spin frequency spend a substantial amount of time at these `resonance' temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot non-accreting rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB (qLMXB) candidates. We also impose a new theoretical limit on the neutron star spin frequency, explaining the cut-off spin frequency ~730 Hz, following from the statistical analysis of accreting milli...

  19. Measuring the basic parameters of neutron stars using model atmospheres

    CERN Document Server

    Suleimanov, V F; Klochkov, D; Werner, K

    2015-01-01

    Model spectra of neutron star atmospheres are nowadays widely used to fit the observed thermal X-ray spectra of neutron stars. This fitting is the key element in the method of the neutronstar radius determination. Here, we present the basic assumptions used for the neutron star atmosphere modeling as well as the main qualitative features of the stellar atmospheres leading to the deviations of the emergent model spectrum from blackbody. We describe the properties of two of our model atmosphere grids: (i) pure carbon atmospheres for relatively cool neutron stars (1--4 MK) and (ii) hot atmospheres with Compton scattering taken into account. The results obtained by applying these grids to model the X-ray spectra of the central compact object in supernova remnant HESS 1731-347, and two X-ray bursting neutron stars in low-mass X-ray binaries, 4U 1724-307 and 4U 1608-52, are presented. Possible systematic uncertainties associated with the obtained neutron star radii are discussed.

  20. General Relativistic Simulations of Binary Neutron Star Mergers

    Science.gov (United States)

    Giacomazzo, Bruno; Rezzolla, Luciano; Baiotti, Luca; Link, David; Font, José A.

    2011-08-01

    Binary neutron star mergers are one of the possible candidates for the central engine of short gamma-ray bursts (GRBs) and they are also powerful sources of gravitational waves. We have used our fully general relativistic hydrodynamical code Whisky to investigate the merger of binary neutron star systems and we have in particular studied the properties of the tori that can be formed by these systems, their possible connection with the engine of short GRBs and the gravitational wave signals that detectors such as advanced LIGO will be able to detect. We have also shown how the mass of the torus varies as a function of the total mass of the neutron stars composing the binary and of their mass ratio and we have found that tori sufficiently massive to power short GRBs can indeed be formed.

  1. Upper limits on the rates of binary neutron star and neutron-star--black-hole mergers from Advanced LIGO's first observing run

    CERN Document Server

    Abbott, B P; 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; 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, 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; Boer, M; Bogaert, G; Bogan, C; Bohe, A; 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; Broida, J E; Brooks, A F; Brown, D A; Brown, D 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; Bustillo, J Calder'on; Callister, T; Calloni, E; Camp, J B; Cannon, K C; Cao, J; Capano, C D; Capocasa, E; Carbognani, F; Caride, S; Diaz, J Casanueva; Casentini, C; Caudill, S; Cavagli`a, M; Cavalier, F; Cavalieri, R; Cella, G; Cepeda, C B; Baiardi, L Cerboni; Cerretani, G; Cesarini, E; Chamberlin, S J; Chan, M; Chao, S; Charlton, P; 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, 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; 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; Canton, T Dal; Danilishin, S L; D'Antonio, S; Danzmann, K; Darman, N S; Dasgupta, A; Costa, C F Da Silva; 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; Del'eglise, S; Del Pozzo, W; Denker, T; Dent, T; Dergachev, V; De Rosa, R; DeRosa, R T; DeSalvo, R; Devine, R C; Dhurandhar, S; D'iaz, M C; Di Fiore, L; Di Giovanni, M; 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, 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; 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; Garufi, F; 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; Glaefke, A; Goetz, E; Goetz, R; Gondan, L; Gonz'alez, G; Castro, J M Gonzalez; Gopakumar, A; Gordon, N A; Gorodetsky, M L; Gossan, S E; Gosselin, M; Gouaty, R; Grado, A; 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; Henry, J; 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, H; Jani, K; Jaranowski, P; Jawahar, S; Jian, L; Jim'enez-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; Kapadia, S J; Karki, S; Karvinen, K S; Kasprzack, M; Katsavounidis, E; Katzman, W; Kaufer, S; Kaur, T; Kawabe, K; K'ef'elian, F; Kehl, M S; Keitel, D; Kelley, D B; Kells, W; Kennedy, R; Key, J S; Khalili, F Y; Khan, I; Khan, S; Khan, Z; Khazanov, E A; Kijbunchoo, N; Kim, Chi-Woong; Kim, Chunglee; Kim, J; Kim, K; Kim, N; 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; Kr'olak, 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; 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; 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; L"uck, 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, F; Marion, F; M'arka, S; M'arka, Z; Markosyan, A S; Maros, E; Martelli, F; 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; Miller, B 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, C J; Moraru, D; Moreno, G; Morriss, S R; Mossavi, K; Mours, B; Mow-Lowry, C M; 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; Nedkova, K; Nelemans, G; Nelson, T J N; 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; 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; 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; Pratt, J; Predoi, V; Prestegard, T; Price, L R; Prijatelj, M; Principe, M; Privitera, S; Prix, R; Prodi, G A; Prokhorov, L; Puncken, O; Punturo, M; Puppo, P; P"urrer, M; Qi, H; Qin, J; Qiu, S; Quetschke, V; Quintero, E A; Quitzow-James, R; Raab, F 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, 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; Rosi'nska, D; Rowan, S; R"udiger, A; Ruggi, P; Ryan, K; Sachdev, 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; Schofield, R M S; Sch"onbeck, A; Schreiber, E; Schuette, D; Schutz, B F; Scott, J; Scott, S M; Sellers, D; Sengupta, A S; Sentenac, D; Sequino, V; Sergeev, A; Setyawati, Y; Shaddock, D A; Shaffer, T; Shahriar, M S; Shaltev, M; Shapiro, B; Shawhan, P; Sheperd, A; Shoemaker, D H; Shoemaker, D M; Siellez, K; Siemens, X; Sieniawska, M; Sigg, D; Silva, A 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; Stone, R; Strain, K A; Straniero, N; Stratta, G; Strauss, N A; Strigin, S; Sturani, R; Stuver, A L; Summerscales, T Z; Sun, L; Sunil, S; Sutton, P J; Swinkels, B L; Szczepa'nczyk, M J; Tacca, M; Talukder, D; Tanner, D B; T'apai, M; Tarabrin, S P; Taracchini, A; Taylor, R; Theeg, T; Thirugnanasambandam, M P; Thomas, E G; Thomas, M; Thomas, P; Thorne, K A; Thrane, E; Tiwari, S; Tiwari, V; Tokmakov, K V; Toland, K; Tomlinson, C; Tonelli, M; Tornasi, Z; Torres, C V; Torrie, C I; T"oyr"a, D; Travasso, F; Traylor, G; Trifir`o, 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; Brand, J F J van den; Broeck, C Van Den; Vander-Hyde, D C; van der Schaaf, L; van Heijningen, J V; van Veggel, A A; Vardaro, M; Vass, S; Vas'uth, M; Vaulin, R; Vecchio, A; Vedovato, G; Veitch, J; Veitch, P J; Venkateswara, K; Verkindt, D; Vetrano, F; Vicer'e, 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, 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; Wen, L; Wessels, P; Westphal, T; Wette, K; Whelan, J T; 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; Woehler, J; Worden, J; Wright, J L; Wu, D S; Wu, G; Yablon, J; Yam, W; Yamamoto, H; Yancey, C C; Yu, H; Yvert, M; zny, A Zadro; 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 Advanced LIGO. In particular we searched for gravitational wave signals from binary neutron star systems with component masses $\\in [1,3] M_{\\odot}$ and component dimensionless spins $< 0.05$. We also searched for neutron-star--black-hole systems with the same neutron star parameters, black hole mass $\\in [2,99] M_{\\odot}$ and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems, and find that they could have detected the merger of binary neutron star systems with component mass distributions of $1.35\\pm0.13 M_{\\odot}$ at a volume-weighted average distance of $\\sim$ 70Mpc, and for neutron-star--black-hole systems with neutron star masses of $1.4M_\\odot$ and black hole masses of at least $5M_\\odot$, a volume-weighted average distance of at least $\\sim$ 110Mpc. From this we...

  2. Can Neutron stars constrain Dark Matter?

    DEFF Research Database (Denmark)

    Kouvaris, Christoforos; Tinyakov, Peter

    2010-01-01

    We argue that observations of old neutron stars can impose constraints on dark matter candidates even with very small elastic or inelastic cross section, and self-annihilation cross section. We find that old neutron stars close to the galactic center or in globular clusters can maintain a surface...... temperature that could in principle be detected. Due to their compactness, neutron stars can acrete WIMPs efficiently even if the WIMP-to-nucleon cross section obeys the current limits from direct dark matter searches, and therefore they could constrain a wide range of dark matter candidates....

  3. Discovery of the near-infrared counterpart to the luminous neutron-star low-mass X-ray binary GX 3+1

    Energy Technology Data Exchange (ETDEWEB)

    Van den Berg, Maureen; Fridriksson, Joel K. [Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Homan, Jeroen [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 70 Vassar Street, Cambridge, MA 02139 (United States); Linares, Manuel, E-mail: M.C.vandenBerg@uva.nl [Instituto de Astrofísica de Canarias (IAC), Vía Láctea s/n, La Laguna, E-38205, S/C de Tenerife (Spain)

    2014-10-01

    Using the High Resolution Camera on board the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position, we have discovered the near-infrared (NIR) counterpart to GX 3+1 in images taken with the PANIC and FourStar cameras on the Magellan Baade Telescope. The identification of this K{sub s} = 15.8 ± 0.1 mag star as the counterpart is based on the presence of a Br γ emission line in an NIR spectrum taken with the Folded-port InfraRed Echelette spectrograph on the Baade Telescope. The absolute magnitude derived from the best available distance estimate to GX 3+1 indicates that the mass donor in the system is not a late-type giant. We find that the NIR light in GX 3+1 is likely dominated by the contribution from a heated outer accretion disk. This is similar to what has been found for the NIR flux from the brighter class of Z sources, but unlike the behavior of atolls fainter (L{sub X} ≈ 10{sup 36}-10{sup 37} erg s{sup –1}) than GX 3+1, where optically thin synchrotron emission from a jet probably dominates the NIR flux.

  4. Discovery of the Near-infrared Counterpart to the Luminous Neutron-star Low-mass X-Ray Binary GX 3+1

    Science.gov (United States)

    van den Berg, Maureen; Homan, Jeroen; Fridriksson, Joel K.; Linares, Manuel

    2014-10-01

    Using the High Resolution Camera on board the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position, we have discovered the near-infrared (NIR) counterpart to GX 3+1 in images taken with the PANIC and FourStar cameras on the Magellan Baade Telescope. The identification of this Ks = 15.8 ± 0.1 mag star as the counterpart is based on the presence of a Br γ emission line in an NIR spectrum taken with the Folded-port InfraRed Echelette spectrograph on the Baade Telescope. The absolute magnitude derived from the best available distance estimate to GX 3+1 indicates that the mass donor in the system is not a late-type giant. We find that the NIR light in GX 3+1 is likely dominated by the contribution from a heated outer accretion disk. This is similar to what has been found for the NIR flux from the brighter class of Z sources, but unlike the behavior of atolls fainter (LX ≈ 1036-1037 erg s-1) than GX 3+1, where optically thin synchrotron emission from a jet probably dominates the NIR flux. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  5. Discovery of the near-infrared counterpart to the luminous neutron-star low-mass X-ray binary GX 3+1

    CERN Document Server

    Berg, Maureen van den; Fridriksson, Joel K; Linares, Manuel

    2014-01-01

    Using the High Resolution Camera onboard the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron-star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position we have discovered the near-infrared (NIR) counterpart to GX 3+1 in images taken with the PANIC and FourStar cameras on the Magellan Baade Telescope. The identification of this K_s=15.8+-0.1 mag star as the counterpart is based on the presence of a Br-gamma emission line in a NIR spectrum taken with the FIRE spectrograph on the Baade Telescope. The absolute magnitude derived from the best available distance estimate to GX 3+1 indicates that the mass donor in the system is not a late-type giant. We find that the NIR light in GX 3+1 is likely dominated by the contribution from a heated outer accretion disk. This is similar to what has been found for the NIR flux from the brighter class of Z sources, but unlike the behavior of atolls fainter (Lx ~ 1e36 to 1e37 erg/s) than G...

  6. Magnetic and spin evolution of neutron stars in close binaries

    CERN Document Server

    Urpin, V; Konenkov, D Y

    1998-01-01

    The evolution of neutron stars in close binary systems with a low-mass companion is considered assuming the magnetic field to be confined within the solid crust. We adopt the standard scenario of the evolution in a close binary system in accordance with which the neutron star passes throughout four evolutionary phases ("isolated pulsar" -- "propeller" -- accretion from the wind of a companion -- accretion due to Roche-lobe overflow). Calculations have been performed for a great variety of parameters characterizing the properties both of the neutron star and low-mass companion. We find that neutron stars with more or less standard magnetic field and spin period being processed in low-mass binaries can evolve to low-field rapidly rotating pulsars. Even if the main-sequence life of a companion is as long as $10^{10}$ yr, the neutron star can maintain a relatively strong magnetic field to the end of the accretion phase. The considered model can well account for the origin of millisecond pulsars.

  7. On the Origin of the Near-infrared Emission from the Neutron-star Low-mass X-Ray Binary GX 9+1

    Science.gov (United States)

    van den Berg, Maureen; Homan, Jeroen

    2017-01-01

    We have determined an improved position for the luminous persistent neutron-star low-mass X-ray binary and atoll source GX 9+1 from archival Chandra X-ray Observatory data. The new position significantly differs from a previously published Chandra position for this source. Based on the revised X-ray position we have identified a new near-infrared (NIR) counterpart to GX 9+1 in K s -band images obtained with the PANIC and FourStar cameras on the Magellan Baade Telescope. NIR spectra of this {K}s=16.5+/- 0.1 mag star, taken with the FIRE spectrograph on the Baade Telescope, show a strong Br γ emission line, which is a clear signature that we discovered the true NIR counterpart to GX 9+1. The mass donor in GX 9+1 cannot be a late-type giant, as such a star would be brighter than the estimated absolute K s magnitude of the NIR counterpart. The slope of the dereddened NIR spectrum is poorly constrained due to uncertainties in the column density N H and NIR extinction. Considering the source’s distance and X-ray luminosity, we argue that N H likely lies near the high end of the previously suggested range. If this is indeed the case, the NIR spectrum is consistent with thermal emission from a heated accretion disk, possibly with a contribution from the secondary. In this respect, GX 9+1 is similar to other bright atolls and the Z sources, whose NIR spectra do not show the slope that is expected for a dominant contribution from optically thin synchrotron emission from the inner regions of a jet. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  8. Constraining the neutron star equation of state with gravitational wave signals from coalescing binary neutron stars

    CERN Document Server

    Agathos, Michalis; Del Pozzo, Walter; Li, Tjonnie G F; Tompitak, Marco; Veitch, John; Vitale, Salvatore; Broeck, Chris Van Den

    2015-01-01

    Recently exploratory studies were performed on the possibility of constraining the neutron star equation of state (EOS) using signals from coalescing binary neutron stars, or neutron star-black hole systems, as they will be seen in upcoming advanced gravitational wave detectors such as Advanced LIGO and Advanced Virgo. In particular, it was estimated to what extent the combined information from multiple detections would enable one to distinguish between different equations of state through hypothesis ranking or parameter estimation. Under the assumption of zero neutron star spins both in signals and in template waveforms and considering tidal effects to 1PN order, it was found that O(20) sources would suffice to distinguish between a hard, moderate, and soft equation of state. Here we revisit these results, this time including neutron star tidal effects to the highest order currently known, termination of gravitational waveforms at the contact frequency, neutron star spins, and the resulting quadrupole-monopo...

  9. Neutron Star Dense Matter Equation of State Constraints with NICER

    Science.gov (United States)

    Bogdanov, Slavko; Arzoumanian, Zaven; Chakrabarty, Deepto; Guillot, Sebastien; Kust Harding, Alice; Ho, Wynn C. G.; Lamb, Frederick K.; Mahmoodifar, Simin; Miller, M. Coleman; Morsink, Sharon; Ozel, Feryal; Psaltis, Dimitrios; Ray, Paul S.; Riley, Tom; Strohmayer, Tod E.; Watts, Anna; Wolff, Michael Thomas; Gendreau, Keith

    2017-08-01

    One of the principal goals of the Neutron Star Interior Composition Explorer (NICER) is to place constraints on the dense matter equation of state through sensitive X-ray observations of neutron stars. The NICER mission will focus on measuring the masses and radii of several relatively bright, thermally-emitting, rotation-powered millisecond pulsars, by fitting models that incorporate all relevant relativistic effects and atmospheric radiation transfer processes to their periodic soft X-ray modulations. Here, we provide an overview of the targets NICER will observe and tthe technique and models that have been developed by the NICER team to estimate the masses and radii of these pulsars.

  10. Is There a Crisis in Neutron Star Physics?

    CERN Document Server

    Horvath, J E

    2013-01-01

    We shall show in this report that the theoretical evolution of a particular class of systems containing a neutron star, the so-called "black widow" binaries, suggest masses above the $\\sim 2 M_{\\odot}$, a fact that would bring serious concerns about the right description of the equation of state above the saturation density. Moreover, so far the actual determinations of masses for these systems consistently give values above $2 M_{\\odot}$, reinforcing the quandary. In this sense, and given that the confirmation of these ideas would create problems for the microphysical description, we argue that a crisis could be "in the works" in neutron star physics.

  11. Neutron-star matter within the energy-density functional theory and neutron-star structure

    Energy Technology Data Exchange (ETDEWEB)

    Fantina, A. F.; Chamel, N.; Goriely, S. [Institut d' Astronomie et d' Astrophysique, CP226, Université Libre de Bruxelles (ULB), 1050 Brussels (Belgium); Pearson, J. M. [Dépt. de Physique, Université de Montréal, Montréal (Québec), H3C 3J7 (Canada)

    2015-02-24

    In this lecture, we will present some nucleonic equations of state of neutron-star matter calculated within the nuclear energy-density functional theory using generalized Skyrme functionals developed by the Brussels-Montreal collaboration. These equations of state provide a consistent description of all regions of a neutron star. The global structure of neutron stars predicted by these equations of state will be discussed in connection with recent astrophysical observations.

  12. Upper Limits on the Rates of Binary Neutron Star and Neutron Star-Black Hole Mergers from Advanced LIGO’s First Observing Run

    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.; 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, 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.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; 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.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. 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.; 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. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; 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, 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.; 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.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; 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, 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.; 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.; Garufi, F.; 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.; 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.; Grado, A.; 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.; Henry, J.; 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, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; 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.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, N.; 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.; Królak, 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.; 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.; 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.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; 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.; 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.; Miller, B. 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, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; 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.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; 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.; 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.; 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.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. 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, 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.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, 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.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. 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.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; 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.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; 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. V.; 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.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; 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.; Woehler, J.; Worden, J.; Wright, J. L.; Wu, D. S.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; Zadrożny, 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.; LIGO Scientific Collaboration; Virgo Collaboration

    2016-12-01

    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 signals from binary-neutron star systems with component masses \\in [1,3] {M}⊙ and component dimensionless spins detected the merger of binary-neutron star systems with component mass distributions of 1.35 ± 0.13 M ⊙ at a volume-weighted average distance of ˜70 Mpc, and for neutron star-black hole systems with neutron star masses of 1.4 M ⊙ and black hole masses of at least 5 M ⊙, a volume-weighted average distance of at least ˜110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc-3 yr-1 for binary-neutron star systems and less than 3600 Gpc-3 yr-1 for neutron star-black hole systems. We discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. However, we find that if no detection of neutron star-binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of {10}-7+20 Gpc-3 yr-1, short gamma-ray bursts beamed toward the Earth, and assuming that all short gamma-ray bursts have binary-neutron star (neutron star-black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\\buildrel{\\circ}\\over{.} {3}-1.1+1.7 (4\\buildrel{\\circ}\\over{.} {3}-1.9+3.1).

  13. Plasma physics of accreting neutron stars

    Science.gov (United States)

    Ghosh, Pranab; Lamb, Frederick K.

    1991-01-01

    Plasma concepts and phenomena that are needed to understand X- and gamma-ray sources are discussed. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discussed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of accretion by magnetic neutron stars and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from Keplerian disks is then considered in some detail. The radial structure of geometrically thin disk flows, the interaction of disk flows with the neutron star magnetosphere, and models of steady accretion from Keplerian disks are described. Accretion torques and the resulting changes in the spin frequencies of rotating neutron stars are considered. The predicted behavior is then compared with observations of accretion-powered pulsars. Magnetospheric processes that may accelerate particles to very high energies, producing GeV and, perhaps, TeV gamma-rays are discussed. Finally, the mechanisms that decelerate and eventually stop accreting plasma at the surfaces of strongly magnetic neutron stars are described.

  14. Neutron Star Science with the NuSTAR

    Energy Technology Data Exchange (ETDEWEB)

    Vogel, J. K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  15. Gravitational waves from neutron-star mergers

    Science.gov (United States)

    Read, Jocelyn; Cullen, Torrey; Flynn, Eric; Lockett-Ruiz, Veronica; Park, Conner; Vong, Susan

    2016-03-01

    The inspiral and merger of binary neutron stars is expected to provide many signals for Advanced LIGO at design sensitivity. The waveform models currently used to search for and parameterize these signals ignore effects near the merger: as the stars coalesce, the gravitational waves depend additionally on the properties of matter in the core of the stars. In this talk, I will discuss potential systematic error from neglecting these features and present phenomenological waveform models currently being developed to capture the dynamics of merging neutron stars.

  16. Physical Environment of Accreting Neutron Stars

    Directory of Open Access Journals (Sweden)

    J. Wang

    2016-01-01

    Full Text Available Neutron stars (NSs powered by accretion, which are known as accretion-powered NSs, always are located in binary systems and manifest themselves as X-ray sources. Physical processes taking place during the accretion of material from their companions form a challenging and appealing topic, because of the strong magnetic field of NSs. In this paper, we review the physical process of accretion onto magnetized NS in X-ray binary systems. We, firstly, give an introduction to accretion-powered NSs and review the accretion mechanism in X-ray binaries. This review is mostly focused on accretion-induced evolution of NSs, which includes scenario of NSs both in high-mass binaries and in low-mass systems.

  17. Iron-line and continuum variations in the XMM-Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636-53

    NARCIS (Netherlands)

    Lyu, Ming; Méndez, Mariano; Sanna, Andrea; Homan, Jeroen; Belloni, Tomaso; Hiemstra, Beike

    2014-01-01

    We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636-53. We modelled the spectra with two thermal components (representing the accretion disc and

  18. Iron-line and continuum variations in the XMM-Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636-53

    NARCIS (Netherlands)

    Lyu, Ming; Mendez, Mariano; Belloni, Tomaso; Homan, Jeroen; Sanna, Andrea; Hiemstra, Beike

    2014-01-01

    We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636-53 as a function of the position of the source in the colour-colour diagram. We modelled the

  19. Iron-line and continuum variations in the XMM-Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636-53

    NARCIS (Netherlands)

    Lyu, Ming; Mendez, Mariano; Belloni, Tomaso; Homan, Jeroen; Sanna, Andrea; Hiemstra, Beike

    2014-01-01

    We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636-53 as a function of the position of the source in the colour-colour diagram. We modelled the

  20. 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...

  1. Transport coefficients in superfluid neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Tolos, Laura [Instituto de Ciencias del Espacio (IEEC/CSIC) Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Frankfurt Institute for Advances Studies. Johann Wolfgang Goethe University, Ruth-Moufang-Str. 1, 60438 Frankfurt am Main (Germany); Manuel, Cristina [Instituto de Ciencias del Espacio (IEEC/CSIC) Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Sarkar, Sreemoyee [Tata Institute of Fundamental Research, Homi Bhaba Road, Mumbai-400005 (India); Tarrus, Jaume [Physik Department, Technische Universität München, D-85748 Garching (Germany)

    2016-01-22

    We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.

  2. 2D Cooling of Magnetized Neutron Stars

    CERN Document Server

    Aguilera, Deborah N; Miralles, Juan A

    2007-01-01

    Context: Many thermally emitting isolated neutron stars have magnetic fields larger than 10^{13}G. A realistic cooling model should be reconsidered including the presence of high magnetic fields. Aims: We investigate the effects of anisotropic temperature distribution and Joule heating on the cooling of magnetized neutron stars. Methods: The 2D heat transfer equation with anisotropic thermal conductivity tensor and including all relevant neutrino emission processes is solved for realistic models of the neutron star interior and crust. Results: The presence of the magnetic field affects significantly the thermal surface distribution and the cooling history during both, the early neutrino cooling era and the late photon cooling era. Conclusions: There is a huge effect of the Joule heating on the thermal evolution of strongly magnetized neutron stars. Magnetic fields and Joule heating play a key role in maintaining magnetars warm for a long time. Moreover, this effect is also important for intermediate field neu...

  3. Transport coefficients in superfluid neutron stars

    CERN Document Server

    Tolos, Laura; Sarkar, Sreemoyee; Tarrus, Jaume

    2014-01-01

    We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.

  4. Rapidly rotating neutron stars in $R$-squared gravity

    CERN Document Server

    Yazadjiev, Stoytcho S; Kokkotas, Kostas D

    2015-01-01

    $f(R)$ theories of gravity are one of the most popular alternative explanations for dark energy and therefore studying the possible astrophysical implications of these theories is an important task. In the present paper we make a substantial advance in this direction by considering rapidly rotating neutron stars in $R^2$ gravity. The results are obtained numerically and the method we use is non-perturbative and self-consistent. The neutron star properties, such as mass, radius and moment of inertia, are studied in detail and the results show that rotation magnifies the deviations from general relativity and the maximum mass and moment of inertia can reach very high values. This observation is similar to previous studies of rapidly rotating neutron stars in other alternative theories of gravity, such as the scalar-tensor theories, and it can potentially lead to strong astrophysical manifestations.

  5. A propelling neutron star in the enigmatic Be-star γ Cassiopeia

    Science.gov (United States)

    Postnov, K.; Oskinova, L.; Torrejón, J. M.

    2017-02-01

    γ Cassiopeia (γ Cas), is known to be a binary system consisting of a Be-type star and a low-mass (M ˜ 1 M⊙) companion of unknown nature orbiting in the Be-disc plane. Here, we apply the quasi-spherical accretion theory on to a compact magnetized star and show that if the low-mass companion of γ Cas is a fast spinning neutron star, the key observational signatures of γ Cas are remarkably well reproduced. Direct accretion on to this fast rotating neutron star is impeded by the propeller mechanism. In this case, around the neutron star magnetosphere a hot shell is formed which emits thermal X-rays in qualitative and quantitative agreement with observed properties of the X-ray emission from γ Cas. We suggest that γ Cas and its analogues constitute a new subclass of Be-type X-ray binaries hosting rapidly rotating neutron stars formed in supernova explosions with small kicks. The subsequent evolutionary stage of γ Cas and its analogues should be the X Per-type binaries comprising low-luminosity slowly rotating X-ray pulsars. The model explains the enigmatic X-ray emission from γ Cas, and also establishes evolutionary connections between various types of rotating magnetized neutron stars in Be-binaries.

  6. Nuclear Equation of State and Neutron Star Cooling

    CERN Document Server

    Lim, Yeunhwan; Lee, Chang-Hwan

    2015-01-01

    We investigate the effects of the nuclear equation of state (EoS) to the neutron star cooling. New era for nuclear EoS has begun after the discovery of $\\sim 2\\msun$ neutron stars PSR J1614$-$2230 and PSR J0348$+$0432 [1, 2]. Also recent works on the mass and radius of neutron stars from low-mass X-ray binaries [3] strongly constrain the EoS of nuclear matter. On the other hand, observations of the neutron star in Cassiopeia A (Cas A) more than 10 years confirmed the existence of nuclear superfluidity [4, 5]. Nuclear superfluidity reduces the heat capacities as well as neutrino emissivities. With nuclear superfluidity the neutrino emission processes are highly suppressed, and the existence of superfluidity makes the cooling path quite different from that of the standard cooling process. Superfluidity also allows new neutrino emission process, which is called `Pair Breaking and Formation'(PBF). PBF is a fast cooling process and can explain the fast cooling rate of neutron star in Cas A. Therefore, it is essent...

  7. The Fate of the Compact Remnant in Neutron Star Mergers

    CERN Document Server

    Fryer, Chris L; Ramirez-Ruiz, Enrico; Rosswog, Stephan; Shen, Gang; Steiner, Andrew W

    2015-01-01

    Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO 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 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 gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constr...

  8. Evolution of Neutron Star Magnetic Fields

    Indian Academy of Sciences (India)

    Dipankar Bhattacharya

    2002-03-01

    This paper reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems. Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic screening of the field by accreted plasma, are reviewed.

  9. Unified description of dense matter in neutron stars and magnetars

    CERN Document Server

    Chamel, N; Mihailov, L M; Velchev, Ch J; Stoyanov, Zh K; Mutafchieva, Y D; Ivanovich, M D; Fantina, A F; Pearson, J M; Goriely, S

    2013-01-01

    We have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.

  10. Cooling of Accretion-Heated Neutron Stars

    Indian Academy of Sciences (India)

    Rudy Wijnands; Nathalie Degenaar; Dany Page

    2017-09-01

    We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

  11. Rotation at 1122 Hz and the neutron star structure

    CERN Document Server

    Bejger, M; Zdunik, J L

    2006-01-01

    Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. Such rotation imposes bounds on the structure of neutron star in XTE J1739-285. These bounds may be used to constrain poorly known equation of state of dense matter. One-parameter families of stationary configurations rotating rigidly at 1122 Hz are constructed, using a precise 2-D code solving Einstein equations. Hydrostatic equilibrium solutions are tested for stability with respect to axi-symmetric perturbations. A set of ten diverse EOSs of neutron stars is considered. Hypothetical strange stars are also studied. For each EOS, the family of possible neutron star models is limited by the mass shedding limit, corresponding to maximum allowed equatorial radius, R_max, and by the instability with respect to the axi-symmetric perturbations, reached at the minimum allowed equatorial radius, R_min. We get R_min \\simeq 10-13km, and R_max \\simeq 16-18km, with allowed mass 1.4-2.3 M_\\odot. Allowed stars with hyperonic ...

  12. Superfluid hydrodynamics in the inner crust of neutron stars

    CERN Document Server

    Martin, Noël

    2016-01-01

    The inner crust of neutron stars is supposed to be inhomogeneous and composed of dense structures (clusters) that are immersed in a dilute gas of unbound neutrons. Here we consider spherical clusters forming a BCC crystal and cylindrical rods arranged in a hexagonal lattice. We study the relative motion of these dense structures and the neutron gas using superfluid hydrodynamics. Within this approach, which relies on the assumption that Cooper pairs are small compared to the crystalline structures, we find that the entrainment of neutrons by the clusters is very weak since neutrons of the gas can flow through the clusters. Consequently, we obtain a low effective mass of the clusters and a superfluid density that is even higher than the density of unbound neutrons. Consequences for the constraints from glitch observations are discussed.

  13. Superfluid hydrodynamics in the inner crust of neutron stars

    Science.gov (United States)

    Martin, Noël; Urban, Michael

    2016-12-01

    The inner crust of neutron stars is supposed to be inhomogeneous and composed of dense structures (clusters) that are immersed in a dilute gas of unbound neutrons. Here we consider spherical clusters forming a body-centered cubic (BCC) crystal and cylindrical rods arranged in a hexagonal lattice. We study the relative motion of these dense structures and the neutron gas using superfluid hydrodynamics. Within this approach, which relies on the assumption that Cooper pairs are small compared to the crystalline structures, we find that the entrainment of neutrons by the clusters is very weak since neutrons of the gas can flow through the clusters. Consequently, we obtain a low effective mass of the clusters and a superfluid density that is even higher than the density of unbound neutrons. Consequences for the constraints from glitch observations are discussed.

  14. 3D General Relativistic Simulations of Coalescing Binary Neutron Stars

    CERN Document Server

    Oohara, K I; Nakamura, Takashi; Oohara, Ken-ichi

    1999-01-01

    We develop a 3 dimensional computer code to study a coalescing neutron star binary. The code can currently follow the evolution up to two stars begin to merge from two spherical stars of mass 1 solar mass and radius 8.9km with separation 35.4km. As for coordinate conditions, we use conformal slicing and pseudo-minimal distortion conditions. The evolution equations for the metric is integrated using the CIP method while the van Leer's scheme is used to integrate the equations for the matter. We present a few results of our simulations including gravitational radiation.

  15. Double Neutron Stars: Evidence For Two Different Neutron-Star Formation Mechanisms

    NARCIS (Netherlands)

    van den Heuvel, E.P.J.

    2007-01-01

    Six of the eight double neutron stars known in the Galactic disk have low orbital eccentricities (< 0.27) indicating that their second-born neutron stars received only very small velocity kicks at birth. This is similar to the case of the B-emission X-ray binaries, where a sizable fraction of the ne

  16. Axion star collisions with neutron stars and fast radio bursts

    Science.gov (United States)

    Raby, Stuart

    2016-11-01

    Axions may make a significant contribution to the dark matter of the Universe. It has been suggested that these dark matter axions may condense into localized clumps, called "axion stars." In this paper we argue that collisions of dilute axion stars with neutron stars, of the type known as "magnetars," may be the origin of most of the observed fast radio bursts. This idea is a variation of an idea originally proposed by Iwazaki. However, instead of the surface effect of Iwazaki, we propose a perhaps stronger volume effect caused by the induced time dependent electric dipole moment of neutrons.

  17. Axion star collisions with Neutron stars and Fast Radio Bursts

    CERN Document Server

    Raby, Stuart

    2016-01-01

    Axions may make a significant contribution to the dark matter of the universe. It has been suggested that these dark matter axions may condense into localized clumps, called "axion stars." In this paper we argue that collisions of dilute axion stars with neutron stars may be the origin of most of the observed fast radio bursts. This idea is a variation of an idea originally proposed by Iwazaki. However, instead of the surface effect of Iwazaki, we propose a perhaps stronger volume effect caused by the induced time dependent electric dipole moment of neutrons.

  18. Symmetry energy effects in the neutron star crust properties

    CERN Document Server

    Porebska, J

    2009-01-01

    Different shapes of the nuclear symmetry energy leads to a different crust-core transition point in the neutron star. The basic properties of a crust, like thickness, mass and moment of inertia were investigated for various forms of the symmetry energy.

  19. Deconfinement phase transition in neutron star matter

    Institute of Scientific and Technical Information of China (English)

    LI Ang; PENG Guang-Xiong; Lombardo U

    2009-01-01

    The transition from hadron phase to strange quark phase in dense matter is investigated. Instead of using the conventional bag model in quark sect, we achieve the confinement by a density-dependent quark mass derived from in-medium chiral condensates, with a thermodynamic problem improved. In nuclear slot,we adopt the equation of state from Brueckner-Bethe-Goldstone approach with three-body force. It is found that the mixed phase can occur, for reasonable confinement parameter, near the normal saturation density,and transit to pure quark matter at 4-5 times the saturation, which is quite different from the previous results from other quark models that pure quark phase can not appear at neutron-star densities.

  20. Optically thick envelopes around ULXs powered by accreating neutron stars

    Science.gov (United States)

    Mushtukov, Alexander A.; Suleimanov, Valery F.; Tsygankov, Sergey S.; Ingram, Adam

    2017-01-01

    Magnetized neutron stars power at least some ultra-luminous X-ray sources. The accretion flow in these cases is interrupted at the magnetospheric radius and then reaches the surface of a neutron star following magnetic field lines. Accreting matter moving along magnetic field lines forms the accretion envelope around the central object. We show that, in case of high mass accretion rates ≳ 1019 g s-1 the envelope becomes closed and optically thick, which influences the dynamics of the accretion flow and the observational manifestation of the neutron star hidden behind the envelope. Particularly, the optically thick accretion envelope results in a multi-color black-body spectrum originating from the magnetospheric surface. The spectrum and photon energy flux vary with the viewing angle, which gives rise to pulsations characterized by high pulsed fraction and typically smooth pulse profiles. The reprocessing of radiation due to interaction with the envelope leads to the disappearance of cyclotron scattering features from the spectrum. We speculate that the super-orbital variability of ultra-luminous X-ray sources powered by accreting neutron stars can be attributed to precession of the neutron star due to interaction of magnetic dipole with the accretion disc.

  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. 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.

  3. Cooling of neutron stars and hybrid stars with a stiff hadronic EoS

    CERN Document Server

    Grigorian, H; Voskresensky, D N

    2015-01-01

    Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the masses of the pulsars PSR J1616-2230, PSR J0348-0432 and J00737-3039B and the companion of J1756-2251 provide independent proof for the existence of neutron stars with masses in a broad range from 1.2 to 2 $M_\\odot$. The values $M>2 M_{\\odot}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4~M_\\odot$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner co...

  4. A propelling neutron star in the enigmatic Be-star $\\gamma$~Cassiopeia

    CERN Document Server

    Postnov, K; Torrejón, J M

    2016-01-01

    The enigmatic X-ray emission from the bright optical star, $\\gamma$ Cassiopeia, is a long-standing problem. $\\gamma$ Cas is known to be a binary system consisting of a Be-type star and a low-mass ($M\\sim 1\\,M_\\odot$) companion of unknown nature orbiting in the Be-disk plane. Here we apply the quasi-spherical accretion theory onto a compact magnetized star and show that if the low-mass companion of $\\gamma$ Cas is a fast spinning neutron star, the key observational signatures of $\\gamma$ Cas are remarkably well reproduced. Direct accretion onto this fast rotating neutron star is impeded by the propeller mechanism. In this case, around the neutron star magnetosphere a hot shell is formed that emits thermal X-rays in qualitative and quantitative agreement with observed properties of the X-ray emission from $\\gamma$ Cas. We suggest that $\\gamma$ Cas and its analogs constitute a new subclass of Be-type X-ray binaries hosting rapidly rotating neutron stars formed in supernova explosions with small kicks. The subseq...

  5. Neutron Stars in X-ray Binaries and their Environments

    Science.gov (United States)

    Paul, Biswajit

    2017-09-01

    Neutron stars in X-ray binary systems are fascinating objects that display a wide range of timing and spectral phenomena in the X-rays. Not only parameters of the neutron stars, like magnetic field strength and spin period evolve in their active binary phase, the neutron stars also affect the binary systems and their immediate surroundings in many ways. Here we discuss some aspects of the interactions of the neutron stars with their environments that are revelaed from their X-ray emission. We discuss some recent developments involving the process of accretion onto high magnetic field neutron stars: accretion stream structure and formation, shape of pulse profile and its changes with accretion torque. Various recent studies of reprocessing of X-rays in the accretion disk surface, vertical structures of the accretion disk and wind of companion star are also discussed here. The X-ray pulsars among the binary neutron stars provide excellent handle to make accurate measurement of the orbital parameters and thus also evolution of the binray orbits that take place over time scale of a fraction of a million years to tens of millions of years. The orbital period evolution of X-ray binaries have shown them to be rather complex systems. Orbital evolution of X-ray binaries can also be carried out from timing of the X-ray eclipses and there have been some surprising results in that direction, including orbital period glitches in two X-ray binaries and possible detection of the most massive circum-binary planet around a Low Mass X-ray Binary.

  6. Gravitational radiation and gamma-ray bursts from accreting neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Mosquera Cuesta, H.J.; Araujo, J.C.N. de; Aguiar, O.D. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Div. de Astrofisica]. E-mail: herman@das.inpe.br; jcarlos@das.inpe.br; odylio@das.inpe.br; Horvath, J.E. [Sao Paulo Univ., SP (Brazil). Inst. Astronomico e Geofisico]. E-mail: foton@orion.iagusp.usp.br

    2000-07-01

    It is well known that hydrodynamic instabilities can be induced in rapidly rotating low magnetic field neutron stars, which accrete mass from a companion in both high and low mass X-ray binaries. (author)

  7. Quark-novae in neutron star-white dwarf binaries: a model for luminous (spin-down powered) sub-Chandrasekhar-mass Type Ia supernovae?

    Institute of Scientific and Technical Information of China (English)

    Rachid Ouyed; Jan Staff

    2013-01-01

    We show that,by appealing to a Quark-Nova (QN) in a tight binary system containing a massive neutron star and a CO white dwarf (WD),a Type Ia explosion could occur.The QN ejecta collides with the WD,driving a shock that triggers carbon burning under degenerate conditions (the QN-Ia).The conditions in the compressed low-mass WD (MWD < 0.9 M☉) in our model mimic those of a Chandrasekhar mass WD.The spin-down luminosity from the QN compact remnant (the quark star) provides additional power that makes the QN-Ia light-curve brighter and broader than a standard SN-Ia with similar 56Ni yield.In QNe-Ia,photometry and spectroscopy are not necessarily linked since the kinetic energy of the ejecta has a contribution from spin-down power and nuclear decay.Although QNe-Ia may not obey the Phillips relationship,their brightness and their relatively "normal looking" light-curves mean they could be included in the cosmological sample.Light-curve fitters would be confused by the discrepancy between spectroscopy at peak and photometry and would correct for it by effectively brightening or dimming the QNe-Ia apparent magnitudes,thus over-or under-estimating the true magnitude of these spin-down powered SNe-Ia.Contamination of QNe-Ia in samples of SNe-Ia used for cosmological analyses could systematically bias measurements of cosmological parameters if QNe-Ia are numerous enough at high-redshift.The strong mixing induced by spin-down wind combined with the low 56Ni yields in QNe-Ia means that these would lack a secondary maximum in the i-band despite their luminous nature.We discuss possible QNe-Ia progenitors.

  8. Ultra-stripped supernovae and double neutron star systems

    CERN Document Server

    Tauris, Thomas

    2015-01-01

    The evolution of close-orbit progenitor binaries of double neutron star (DNS) systems leads to supernova (SN) explosions of ultra-stripped stars. The amount of SN ejecta mass is very limited from such, more or less, naked metal cores with envelope masses of only 0.01-0.2 Msun. The combination of little SN ejecta mass and the associated possibility of small NS kicks is quite important for the characteristics of the resulting DNS systems left behind. Here, we discuss theoretical predictions for DNS systems, based on Case BB Roche-lobe overflow prior to ultra-stripped SNe, and briefly compare with observations.

  9. Outflows from neutron star merger remnant disks: nucleosynthesis and kilonovae

    Science.gov (United States)

    Fernandez, Rodrigo; Lippuner, Jonas; Roberts, Luke; Tchekhovskoy, Alexander; Foucart, Francois; Metzger, Brian; Kasen, Daniel; Quataert, Eliot

    2016-03-01

    The accretion disk formed in a neutron star merger can drive powerful winds on timescales of 100ms to seconds after coalescence. The wind material is more strongly irradiated by neutrinos than the dynamical ejecta, and hence has a less neutron-rich composition, with implications for r-process element synthesis and the radioactively-powered kilonova transient. This talk will present preliminary results from projects aimed at quantifying (1) the nucleosynthesis yield from disks around hypermassive neutron stars, (2) the effect of MHD turbulence on mass ejection when a black hole sits at the center, and (3) the interaction between disk wind and dynamical ejecta when the relative masses of these components vary.

  10. Discovery of the Near-infrared Counterpart to the Luminous Neutron-star Low-mass X-Ray Binary GX 3+1

    NARCIS (Netherlands)

    van den Berg, M.; Homan, J.; Fridriksson, J.K.; Linares, M.

    2014-01-01

    Using the High Resolution Camera on board the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position, we have discovered the near-infrared (NIR) counterpart

  11. Further stable neutron star models from f(R) gravity

    Energy Technology Data Exchange (ETDEWEB)

    Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I–80126 (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)

    2013-12-01

    Neutron star models in perturbative f(R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f(R) = R+R(e{sup −R/R{sub 0}}−1) model and for R{sup 2} models with logarithmic and cubic corrections are obtained. In the case of R{sup 2} gravity with cubic corrections, we obtain that at high central densities (ρ > 10ρ{sub ns}, where ρ{sub ns} = 2.7 × 10{sup 14} g/cm{sup 3} is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ∼ 1.9M{sub ⊙} (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints)

  12. Low-level accretion in neutron star X-ray binaries

    NARCIS (Netherlands)

    Wijnands, R.; Degenaar, N.; Armas Padilla, M.; Altamirano, D.; Cavecchi, Y.; Linares, M.; Bahramian, A.; Heinke, C.O.

    2015-01-01

    We search the literature for reports on the spectral properties of neutron star low-mass X-ray binaries when they have accretion luminosities between 1034 and 1036 erg s−1, corresponding to roughly 0.01-1 per cent of the Eddington accretion rate for a neutron star. We found that in this luminosity r

  13. Further stable neutron star models from f(R) gravity

    CERN Document Server

    Astashenok, Artyom V; Odintsov, Sergei D

    2013-01-01

    Neutron star models in perturbative $f(R)$ gravity are considered with realistic equations of state. In particular, we consider the FPS and SLy equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for $f(R)=R+R(e^{-R/R_{0}}-1)$ model and for $R^2$ models with logarithmic and cubic corrections are obtained. In the case of $R^2$ gravity with logarithmic corrections with a piecewise equation of state (FPS+quark core), one obtains stars with radii $\\sim 9.5 $ km and masses $\\sim 1.50M_{\\odot}$. In contrast with GR, the minimal radius of neutron star for this equation is 9.9 km. In the case of $R^2$ gravity with cubic corrections, we obtain that at high central densities ($\\rho>10\\rho_{ns}$, where $\\rho_{ns}=2.7\\times 10^{14}$ g/cm$^{3}$ is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass $\\sim 1.9 M_{\\odot}$ (SLy equation) or to 8.5 km with mass $\\sim 1.7M_{\\odot}$ (F...

  14. 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.

  15. The Neutron Star Interior Composition Explorer (NICER)

    Science.gov (United States)

    Wilson-Hodge, Colleen A.; Gendreau, K.; Arzoumanian, Z.

    2014-01-01

    The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Scheduled to be launched in 2016 as an International Space Station payload, NICER will explore the exotic states of matter, using rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2-12 keV) X-ray band. Grazing-incidence "concentrator" optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. The NICER project plans to implement a Guest Observer Program, which includes competitively selected user targets after the first year of flight operations. I will describe NICER and discuss ideas for potential Be/X-ray binary science.

  16. Charged Ising Model of Neutron Star Matter

    CERN Document Server

    Hasnaoui, K H O

    2012-01-01

    Background: The inner crust of a neutron star is believed to consist of Coulomb-frustrated complex structures known as "nuclear pasta" that display interesting and unique low-energy dynamics. Purpose: To elucidate the structure and composition of the neutron-star crust as a function of temperature, density, and proton fraction. Methods: A new lattice-gas model, the "Charged-Ising Model" (CIM), is introduced to simulate the behavior of neutron-star matter. Preliminary Monte Carlo simulations on 30^3 lattices are performed for a variety of temperatures, densities, and proton fractions. Results: Results are obtained for the heat capacity, pair-correlation function, and static structure factor for a variety of conditions appropriate to the inner stellar crust. Conclusions: Although relatively simple, the CIM captures the essence of Coulomb frustration that is required to simulate the subtle dynamics of the inner stellar crust. Moreover, the computationally demanding long-range Coulomb interactions have been pre-c...

  17. Neutron Stars in Supernovae and Their Remnants

    CERN Document Server

    Chevalier, Roger A

    2010-01-01

    The magnetic fields of neutron stars have a large range (~3e10 - 1e15 G). There may be a tendency for more highly magnetized neutron stars to come from more massive stellar progenitors, but other factors must also play a role. When combined with the likely initial periods of neutron stars, the magnetic fields imply a spindown power that covers a large range and is typically dominated by other power sources in supernovae. Distinctive features of power input from pulsar spindown are the time dependence of power and the creation of a low density bubble in the interior of the supernova; line profiles in the late phases are not centrally peaked after significant pulsar rotational energy has been deposited. Clear evidence for pulsar power in objects <300 years old is lacking, which can be attributed to large typical pulsar rotation periods at birth.

  18. Towards a metallurgy of neutron star crusts

    CERN Document Server

    Kobyakov, D

    2013-01-01

    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic (bcc) lattice of nuclei immersed in an essentially uniform electron gas. We show that at densities above that for neutron drip ($\\sim4\\times10^11$) g cm$^{-3}$ or roughly one thousandth of nuclear matter density, the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO$_3$. As a consequence, properties of matter in the inner crust are expected to be much richer than previously appreciated and we mention consequences for observable neutron star properties.

  19. Towards a metallurgy of neutron star crusts.

    Science.gov (United States)

    Kobyakov, D; Pethick, C J

    2014-03-21

    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip (∼ 4 × 1 0(11)  g cm(-3) or roughly one-thousandth of nuclear matter density), the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO3. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties.

  20. Magnetic field evolution in neutron stars

    Science.gov (United States)

    Castillo, F.; Reisenegger, A.; Valdivia, J. A.

    2017-07-01

    Neutron stars contain the strongest magnetic fields known in the Universe. Using numerical simulations restricted to axially symmetric geometry, we study the long-term evolution of the magnetic field in the interior of an isolated neutron star under the effect of ambipolar diffusion, i.e. the drift of the magnetic field and the charged particles relative to the neutrons. We model the stellar interior as an electrically neutral fluid composed of neutrons, protons and electrons; these species can be converted into each other by weak interactions (beta decays), suffer binary collisions, and be affected by each other's macroscopic electromagnetic fields. We show that, in the restricted case of pure ambipolar diffusion, neglecting weak interactions, the magnetic fields evolves towards a stable MHD equilibria configuration, in the timescales analytically expected.

  1. Discovery of a correlation between the frequency of the mHz quasi-periodic oscillations and the neutron-star temperature in the low-mass X-ray binary 4U 1636-53

    CERN Document Server

    Lyu, Ming; Altamirano, Diego

    2014-01-01

    We detected millihertz quasi-periodic oscillations (QPOs) in an XMM-Newton observation of the neutron-star low-mass X-ray binary 4U 1636-53. These QPOs have been interpreted as marginally-stable burning on the neutron-star surface. At the beginning of the observation the QPO was at around 8 mHz, together with a possible second harmonic. About 12 ks into the observation a type I X-ray burst occurred and the QPO disappeared; the QPO reappeared ~25 ks after the burst and it was present until the end of the observation. We divided the observation into four segments to study the evolution of the spectral properties of the source during intervals with and without mHz QPO. We find that the temperature of the neutron-star surface increases from the QPO segment to the non-QPO segment, and vice versa. We also find a strong correlation between the frequency of the mHz QPO and the temperature of a black-body component in the energy spectrum representing the temperature of neutron-star surface. Our results are consistent ...

  2. Spin paramagnetic deformation of a neutron star

    Science.gov (United States)

    Suvorov, A. G.; Mastrano, A.; Melatos, A.

    2016-02-01

    Quantum mechanical corrections to the hydromagnetic force balance equation, derived from the microscopic Schrödinger-Pauli theory of quantum plasmas, modify the equilibrium structure and hence the mass quadrupole moment of a neutron star. It is shown here that the dominant effect - spin paramagnetism - is most significant in a magnetar, where one typically has μ _B|B|≳ k_B T_e, where μB is the Bohr magneton, B is the magnetic field, and Te is the electron temperature. The spin paramagnetic deformation of a non-barotropic magnetar with a linked poloidal-toroidal magnetic field is calculated to be up to ˜10 times greater than the deformation caused solely by the Lorentz force. It depends on the degree of Pauli blocking by conduction electrons and the propensity to form magnetic domains, processes which are incompletely modelled at magnetar field strengths. The star becomes more oblate, as the toroidal field component strengthens. The result implies that existing classical predictions underestimate the maximum strength of the gravitational wave signal from rapidly spinning magnetars at birth. Turning the argument around, future gravitational-wave upper limits of increasing sensitivity will place ever-stricter constraints on the physics of Pauli blocking and magnetic domain formation under magnetar conditions.

  3. Spin paramagnetic deformation of a neutron star

    CERN Document Server

    Suvorov, A G; Melatos, A

    2015-01-01

    Quantum mechanical corrections to the hydromagnetic force balance equation, derived from the microscopic Schr\\"{o}dinger-Pauli theory of quantum plasmas, modify the equilibrium structure and hence the mass quadrupole moment of a neutron star. It is shown here that the dominant effect --- spin paramagnetism --- is most significant in a magnetar, where one typically has $\\mu_{B}|\\boldsymbol{B}|\\gtrsim k_B T_e$, where $\\mu_{B}$ is the Bohr magneton, $\\boldsymbol{B}$ is the magnetic field, and $T_e$ is the electron temperature. The spin paramagnetic deformation of a nonbarotropic magnetar with a linked poloidal-toroidal magnetic field is calculated to be up to ${{\\sim 10}}$ times greater than the deformation caused solely by the Lorentz force. It depends on the degree of Pauli blocking by conduction electrons and the propensity to form magnetic domains, processes which are incompletely modelled at magnetar field strengths. The star becomes more oblate, as the toroidal field component strengthens. The result impli...

  4. Quark matter and the astrophysics of neutron stars

    OpenAIRE

    Prakash, M.

    2007-01-01

    Some of the means through which the possible presence of nearly deconfined quarks in neutron stars can be detected by astrophysical observations of neutron stars from their birth to old age are highlighted.

  5. An instability in neutron stars at birth

    Science.gov (United States)

    Burrows, Adam; Fryxell, Bruce A.

    1992-01-01

    Calculations with a two-dimensional hydrodynamic simulation show that a generic Raleigh-Taylor-like instability occurs in the mantles of nascent neutron stars, that it is possibly violent, and that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. Whether this 'convective' instability is pivotal to the supernova mechanism, pulsar nagnetic fields, or a host of other important issues that attend stellar collapse remains to be seen, but its existence promises to modify all questions concerning this most energetic of astronomical phenomena.

  6. Can neutron stars have auroras ? : electromagnetic coupling process between neutron star and magnetized accretion disk

    Science.gov (United States)

    Kimura, T.; Iwakiri, W. B.; Enoto, T.; Wada, T.; Tao, C.

    2015-12-01

    In the binary neutron star system, angular momentum transfer from accretion disk to a star is essential process for spin-up/down of stars. The angular momentum transfer has been well formulated for the accretion disk strongly magnetized by the neutron star [e.g., Ghosh and Lamb, 1978, 1979a, b]. However, the electromagnetic (EM) coupling between the neutron star and accretion disk has not been self-consistently solved in the previous studies although the magnetic field lines from the star are strongly tied with the accretion disk. In this study, we applied the planet-magnetosphere coupling process established for Jupiter [Hill, 1979] to the binary neutron star system. Angular momentum distribution is solved based on the torque balance between the neutron star's surface and accretion disk coupled by the magnetic field tensions. We found the EM coupling can transfer significantly larger fraction of the angular momentum from the magnetized accretion disk to the star than the unmagnetized case. The resultant spin-up rate is estimated to ~10^-14 [sec/sec] for the nominal binary system parameters, which is comparable with or larger than the other common spin-down/up processes: e.g., the magnetic dipole radiation spin-down. The Joule heating energy dissipated in the EM coupling is estimated to be up to ~10^36 [erg/sec] for the nominal binary system parameters. The release is comparable to that of gravitation energy directly caused by the matters accreting onto the neutron star. This suggests the EM coupling at the neutron star can accompany the observable radiation as auroras with a similar manner to those at the rotating planetary magnetospheres like Jupiter, Saturn, and other gas giants.

  7. Gravitational wave background from rotating neutron stars

    Science.gov (United States)

    Rosado, Pablo A.

    2012-11-01

    The background of gravitational waves produced by the ensemble of rotating neutron stars (which includes pulsars, magnetars, and gravitars) is investigated. A formula for Ω(f) (a function that is commonly used to quantify the background, and is directly related to its energy density) is derived, without making the usual assumption that each radiating system evolves on a short time scale compared to the Hubble time; the time evolution of the systems since their formation until the present day is properly taken into account. Moreover, the formula allows one to distinguish the different parts of the background: the unresolvable (which forms a stochastic background or confusion noise, since the waveforms composing it cannot be either individually observed or subtracted out of the data of a detector) and the resolvable. Several estimations of the background are obtained, for different assumptions on the parameters that characterize neutron stars and their population. In particular, different initial spin period distributions lead to very different results. For one of the models, with slow initial spins, the detection of the background by present or planned detectors can be rejected. However, other models do predict the detection of the background, that would be unresolvable, by the future ground-based gravitational wave detector ET. A robust upper limit for the background of rotating neutron stars is obtained; it does not exceed the detection threshold of two cross-correlated Advanced LIGO interferometers. If gravitars exist and constitute more than a few percent of the neutron star population, then they produce an unresolvable background that could be detected by ET. Under the most reasonable assumptions on the parameters characterizing a neutron star, the background is too faint to be detected. Previous papers have suggested neutron star models in which large magnetic fields (like the ones that characterize magnetars) induce big deformations in the star, which

  8. Are strange stars distinguishable from neutron stars by their cooling behaviour?

    OpenAIRE

    Schaab, Ch.; Hermann, B.; Weber, F.; Weigel, M. K.

    1997-01-01

    The general statement that strange stars cool more rapidly than neutron stars is investigated in greater detail. It is found that the direct Urca process could be forbidden not only in neutron stars but also in strange stars. If so, strange stars would be slowly cooling and their surface temperatures would be more or less indistinguishable from those of slowly cooling neutron stars. The case of enhanced cooling is reinvestigated as well. It is found that strange stars cool significantly more ...

  9. Approximate Universal Relations for Neutron Stars and Quark Stars

    CERN Document Server

    Yagi, Kent

    2016-01-01

    Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia ($I$), its tidal Love number (Love) and its quadrupole moment ($Q$), the so-called I-Love-Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astroph...

  10. Constraining neutron star matter with Quantum Chromodynamics

    CERN Document Server

    Kurkela, Aleksi; Schaffner-Bielich, Jurgen; Vuorinen, Aleksi

    2014-01-01

    In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount --- or even presence --- of quark matter inside the stars.

  11. Constraining neutron star matter with quantum chromodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Kurkela, Aleksi [Physics Department, Theory Unit, CERN, CH-1211 Genève 23 (Switzerland); Fraga, Eduardo S.; Schaffner-Bielich, Jürgen [Institute for Theoretical Physics, Goethe University, D-60438 Frankfurt am Main (Germany); Vuorinen, Aleksi [Department of Physics and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki (Finland)

    2014-07-10

    In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.

  12. Constraining Neutron Star Matter with Quantum Chromodynamics

    Science.gov (United States)

    Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jürgen; Vuorinen, Aleksi

    2014-07-01

    In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.

  13. Role of magnetic interactions in neutron stars

    CERN Document Server

    Adhya, Souvik Priyam

    2016-01-01

    In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case.

  14. Daily, multiwavelength Swift monitoring of the neutron star low-mass X-ray binary Cen X-4: evidence for accretion and reprocessing during quiescence

    CERN Document Server

    Bernardini, F; Brown, E F; Degenaar, C D'Angelo N; Miller, J M; Reynolds, M; Wijnands, R

    2013-01-01

    The physics of accretion during quiescence in low mass X-ray binaries (LMXBs) is poorly understood, yet there are signs that accretion must be happening. Several LMXBs show variability during quiescence, particularly striking is the case of the nearby neutron star Cen X-4. With the goal of unveiling the real nature of its quiescent variability we conducted the first long-term, multiwavelength simultaneous monitoring of Cen X-4, thanks to 60 observations performed by Swift on a daily basis. During those observations, Cen X-4 is highly variable in all energy bands on timescales from days to months, with the strongest quiescent short-term variability detected in the X-ray band, a factor of 22 drop in only 4 days. The X-ray and the UV and optical emission are correlated on timescales down to less than 110 s. The shape of the correlation is a power law with index 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere (kT=59-80 eV) and a power law (spectral index 1.4-2.0). The spectral shape remains...

  15. Two new bursting neutron star low-mass X-ray binaries: Swift J185003.2-005627 and Swift J1922.7-1716

    CERN Document Server

    Degenaar, N; Altamirano, D; Wijnands, R

    2012-01-01

    We discuss the origin of two triggers of Swift's Burst Alert Telescope (BAT) that occurred in 2011. The triggers were identified with Swift J185003.2-005627, a previously unknown X-ray source, and the known but unclassified X-ray transient Swift J1922.7-1716. We investigate the BAT data and follow-up observations obtained with the X-ray and ultra-violet/optical telescopes to demonstrate that both triggers are consistent with thermonuclear X-ray bursts. This implies that both sources are neutron star low-mass X-ray binaries. The total duration of ~7 min and estimated energy output of ~(3-7)E39 erg, fall in between that of normal and intermediately long X-ray bursts. From the observed peaks of the X-ray bursts we estimate a distance of <3.7 kpc for Swift J185003.2-005627 and <4.8 kpc for Swift J1922.7-1716. We characterize the outburst and quiescent X-ray properties of the two sources. They have comparable average outburst luminosities of ~1E35-1E36 erg/s, and a quiescent luminosity equal to or lower than...

  16. XTE J1701-462 and its Implications for the Nature of Subclasses in Low-Magnetic-Field Neutron Star Low-Mass X-Ray Binaries

    CERN Document Server

    Homan, Jeroen; Fridriksson, Joel K; Remillard, Ronald A; Wijnands, Rudy; Mendez, Mariano; Lin, Dacheng; Altamirano, Diego; Casella, Piergiorgio; Belloni, Tomaso; Lewin, Walter H G

    2010-01-01

    We report on an analysis of RXTE data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities the source switched between two types of Z source behavior and at low luminosities we observed a transition from Z source to atoll source behavior. These transitions between subclasses primarily manifest themselves as changes in the shapes of the tracks in X-ray color-color and hardness-intensity diagrams, but they are accompanied by changes in the kHz quasi-periodic oscillations, broad-band variability, burst behavior, and/or X-ray spectra. We find that the low-energy X-ray flux is a good parameter to track the gradual evolution of the tracks in color-color and hardness-intensity diagrams, allowing us to resolve the evolution of the source in greater detail than before and relate the observed properties to other NS-LMXBs. We further find th...

  17. How neutron stars constrain the nuclear equation of state

    CERN Document Server

    Thomas, Hell; Weise, Wolfram

    2013-01-01

    Recent neutron star observations set new constraints for the equation of state of baryonic matter. A chiral effective field theory approach is used for the description of neutron-dominated nuclear matter present in the outer core of neutron stars. Possible hybrid stars with quark matter in the inner core are discussed using a three-flavor Nambu--Jona-Lasinio model.

  18. JD3 - Neutron Stars: Timing in Extreme Environments

    NARCIS (Netherlands)

    Belloni, Tomaso M.; Méndez, Mariano; Zhang, Chengmin

    2009-01-01

    The space-time around Neutron Stars is indeed an extreme environment. Whether they are in accreting binary systems, isolated or in non-accreting binaries (perhaps with another Neutron Star), Neutron Stars provide a window onto physical processes not accessible by other means. In particular, the stud

  19. JD3 - Neutron Stars: Timing in Extreme Environments

    NARCIS (Netherlands)

    Belloni, Tomaso M.; Méndez, Mariano; Zhang, Chengmin

    2010-01-01

    The space-time around Neutron Stars is indeed an extreme environment. Whether they are in accreting binary systems, isolated or in non-accreting binaries (perhaps with another Neutron Star), Neutron Stars provide a window onto physical processes not accessible by other means. In particular, the stud

  20. Extreme neutron stars from Extended Theories of Gravity

    Energy Technology Data Exchange (ETDEWEB)

    Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I-80126 Italy (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)

    2015-01-01

    We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.

  1. Prospects for Neutron Star Equation of State Constraints using "Recycled" Millisecond Pulsars

    CERN Document Server

    Bogdanov, Slavko

    2015-01-01

    Rotation-powered "recycled" millisecond pulsars are a variety of rapidly-spinning neutron stars that typically show thermal X-ray radiation due to the heated surface of their magnetic polar caps. Detailed numerical modeling of the rotation-induced thermal X-ray pulsations observed from recycled millisecond pulsars, including all relevant relativistic and stellar atmospheric effects, has been identified as a promising approach towards an astrophysical determination of the true neutron star mass-radius relation, and by extension the state of cold matter at densities exceeding those of atomic nuclei. Herein, I review the basic model and methodology commonly used to extract information regarding neutron star structure from the pulsed X-ray radiation observed from millisecond pulsars. I also summarize the results of past X-ray observations of these objects and the prospects for precision neutron star mass-radius measurements with the upcoming Neutron Star Interior Composition Explorer (NICER) X-ray timing mission.

  2. Dynamics and gravitational-wave emission of neutron-star merger remnants

    CERN Document Server

    Bauswein, A; Stergioulas, N; Janka, H -T

    2016-01-01

    The coalescence of a neutron-star binary is likely to result in the formation of a neutron-star merger remnant for a large range of binary mass configurations. The massive merger remnant shows strong oscillations, which are excited by the merging process, and emits gravitational waves. Here we discuss possibilities and prospects of inferring unknown stellar properties of neutron stars by the detection of postmerger gravitational-wave emission, which thus leads to constraints of the equation of state of high-density matter. In particular, the dominant oscillation frequency of the postmerger remnant provides tight limits to neutron-star radii. We mention first steps towards a practical implementation of future gravitational-wave searches for the postmerger emission. Moreover, we outline possibilities to estimate the unknown maximum mass of nonrotating neutron stars from such types of measurements. Finally, we review the origin and scientific implications of secondary peaks in the gravitational-wave spectrum of ...

  3. Bose–Einstein condensation of anti-kaons and neutron star twins

    Indian Academy of Sciences (India)

    Sarmistha Banik; Debades Bandyopadhyay

    2003-05-01

    We investigate the role of Bose–Einstein condensation (BEC) of anti-kaons on the equation of state (EoS) and other properties of compact stars. In the framework of relativistic mean field model we determine the EoS for -stable hyperon matter and compare it to the situation when anti-kaons condense in the system. We observe that anti-kaon condensates soften the EoS, thereby lowering the maximum mass of the stars. We also demonstrate that the presence of antikaon condensates in the high density core of compact stars may lead to a new mass sequence beyond white dwarf and neutron stars. The limiting mass of the new sequence stars is nearly equal to that of neutron star branch though they have distinctly different radii and compositions. They are called neutron star twins.

  4. The Mystery of the Lonely Neutron Star

    Science.gov (United States)

    2000-09-01

    The VLT Reveals Bowshock Nebula around RX J1856.5-3754 Deep inside the Milky Way, an old and lonely neutron star plows its way through interstellar space. Known as RX J1856.5-3754 , it measures only ~ 20 km across. Although it is unusually hot for its age, about 700,000 °C, earlier observations did not reveal any activity at all, contrary to all other neutron stars known so far. In order to better understand this extreme type of object, a detailed study of RX J1856.5-3754 was undertaken by Marten van Kerkwijk (Institute of Astronomy of the University of Utrecht, The Netherlands) and Shri Kulkarni (California Institute of Technology, Pasadena, California, USA). To the astronomers' delight and surprise, images and spectra obtained with the ESO Very Large Telescope (VLT) now show a small nearby cone-shaped ("bowshock") nebula. It shines in the light from hydrogen atoms and is obviously a product of some kind of interaction with this strange star. Neutron stars - remnants of supernova explosions Neutron stars are among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). It is the gaseous remnant of a star that exploded in the year 1054 and also left behind a pulsar , i.e., a rotating neutron star [1]. A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth [2]. The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars

  5. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    Science.gov (United States)

    2010-07-01

    raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," explains Crowther. Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years. Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," concludes Crowther. Notes [1] The star A1 in NGC 3603 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they have formed as stars weighing, respectively, 148 and 106 solar masses. [2] The team used the SINFONI, ISAAC and MAD instruments, all attached to ESO's Very Large Telescope at Paranal, Chile. [3] (note added on 26 July 2010) The "bigger" in the title does not imply that these stars are the biggest observed. Such stars, called red supergiants, can have radii up to about a thousand solar radii, while R136a1, which is blue, is about 35 times as large as the Sun. However, R136a1 is the star with the greatest mass known to date. More information This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society ("The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit", by

  6. Dynamics of dissipative multifluid neutron star cores

    NARCIS (Netherlands)

    Haskell, B.; Andersson, N.; Comer, G.L.

    2012-01-01

    We present a Newtonian multifluid formalism for superfluid neutron star cores, focusing on the additional dissipative terms which arise when one takes into account the individual dynamical degrees of freedom associated with the coupled "fluids." The problem is of direct astrophysical interest as the

  7. Neutron Star Interiors and Topology Change

    Directory of Open Access Journals (Sweden)

    Peter K. F. Kuhfittig

    2013-01-01

    Full Text Available Quark matter is believed to exist in the center of neutron stars. A combined model consisting of quark matter and ordinary matter is used to show that the extreme conditions existing in the center could result in a topology change, that is, in the formation of wormholes.

  8. Neutron stars and their magnetic fields

    CERN Document Server

    Reisenegger, Andreas

    2008-01-01

    Neutron stars have the strongest magnetic fields known anywhere in the Universe. In this review, I intend to give a pedagogical discussion of some of the related physics. Neutron stars exist because of Pauli's exclusion principle, in two senses: 1) It makes it difficult to squeeze particles too close together, in this way allowing a mechanical equilibrium state in the presence of extremely strong gravity. 2) The occupation of low-energy proton and electron states makes it impossible for low-energy neutrons to beta decay. A corollary of the second statement is that charged particles are necessarily present inside a neutron star, allowing currents to flow. Since these particles are degenerate, they collide very little, and therefore make it possible for the star to support strong, organized magnetic fields over long times. These show themselves in pulsars and are the most likely energy source for the high X-ray and gamma-ray luminosity ``magnetars''. I briefly discuss the possible origin of this field and some ...

  9. Colliding Neutron Stars as the Source of Heavy Elements

    Science.gov (United States)

    Kohler, Susanna

    2016-09-01

    Where do the heavy elements the chemical elements beyond iron in our universe come from? One of the primary candidate sources is the merger of two neutron stars, but recent observations have cast doubt on this model. Can neutron-star mergers really be responsible?Elements from Collisions?Periodic table showing the origin of each chemical element. Those produced by the r-process are shaded orange and attributed to supernovae in this image; though supernovae are one proposed source of r-process elements, an alternative source is the merger of two neutron stars. [Cmglee]When a binary-neutron-star system inspirals and the two neutron stars smash into each other, a shower of neutrons are released. These neutrons are thought to bombard the surrounding atoms, rapidly producing heavy elements in what is known as r-process nucleosynthesis.So could these mergers be responsible for producing the majority of the universes heavy r-process elements? Proponents of this model argue that its supported by observations. The overall amount of heavy r-process material in the Milky Way, for instance, is consistent with the expected ejection amounts from mergers, based both on predicted merger rates for neutron stars in the galaxy, and on the observed rates of soft gamma-ray bursts (which are thought to accompany double-neutron-star mergers).Challenges from Ultra-Faint DwarfsRecently, however, r-process elements have been observed in ultra-faint dwarf satellite galaxies. This discovery raises two major challenges to the merger model for heavy-element production:When neutron stars are born during a core-collapse supernova, mass is ejected, providing the stars with asymmetric natal kicks. During the second collapse in a double-neutron-star binary, wouldnt the kick exceed the low escape velocity of an ultra-faint dwarf, ejecting the binary before it could merge and enrich the galaxy?Ultra-faint dwarfs have very old stellar populations and the observation of r-process elements in these stars

  10. Neutron Star Structure in the Presence of Conformally Coupled Scalar Fields

    Science.gov (United States)

    Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

    2014-01-01

    Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

  11. Modified TOV in gravity’s rainbow: properties of neutron stars and dynamical stability conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hendi, S.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM),P.O. Box 55134-441, Maragha (Iran, Islamic Republic of); Bordbar, G.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Center for Excellence in Astronomy and Astrophysics (CEAA-RIAAM)-Maragha,P.O. Box 55134-441, Maragha 55177-36698 (Iran, Islamic Republic of); Panah, B. Eslam [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Panahiyan, S. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Physics Department, Shahid Beheshti University,Tehran 19839 (Iran, Islamic Republic of)

    2016-09-09

    In this paper, we consider a spherical symmetric metric to extract the hydrostatic equilibrium equation of stars in (3+1)-dimensional gravity’s rainbow in the presence of cosmological constant. Then, we generalize the hydrostatic equilibrium equation to d-dimensions and obtain the hydrostatic equilibrium equation for this gravity. Also, we obtain the maximum mass of neutron star using the modern equations of state of neutron star matter derived from the microscopic calculations. It is notable that, in this paper, we consider the effects of rainbow functions on the diagrams related to the mass-central mass density (M-ρ{sub c}) relation and also the mass-radius (M-R) relation of neutron star. We also study the effects of rainbow functions on the other properties of neutron star such as the Schwarzschild radius, average density, strength of gravity and gravitational redshift. Then, we apply the cosmological constant to this theory to obtain the diagrams of M-ρ{sub c} (or M-R) and other properties of these stars. Next, we investigate the dynamical stability condition for these stars in gravity’s rainbow and show that these stars have dynamical stability. We also obtain a relation between mass of neutron stars and Planck mass. In addition, we compare obtained results of this theory with the observational data.

  12. Spin evolution of a proto-neutron star

    Science.gov (United States)

    Camelio, Giovanni; Gualtieri, Leonardo; Pons, José A.; Ferrari, Valeria

    2016-07-01

    We study the evolution of the rotation rate of a proto-neutron star, born in a core-collapse supernova, in the first seconds of its life. During this phase, the star evolution can be described as a sequence of stationary configurations, which we determine by solving the neutrino transport and the stellar structure equations in general relativity. We include in our model the angular momentum loss due to neutrino emission. We find that the requirement of a rotation rate not exceeding the mass-shedding limit at the beginning of the evolution implies a strict bound on the rotation rate at later times. Moreover, assuming that the proto-neutron star is born with a finite ellipticity, we determine the emitted gravitational wave signal and estimate its detectability by present and future ground-based interferometric detectors.

  13. Light dark matter scattering in outer neutron star crusts

    CERN Document Server

    Cermeño, Marina; Silk, Joseph

    2016-01-01

    We calculate for the first time the phonon excitation rate in the outer crust of a neutron star due to scattering from light dark matter (LDM) particles gravitationally boosted into the star. We consider dark matter particles in the sub-GeV mass range scattering off a periodic array of nuclei through an effective scalar-vector interaction with nucleons. We find that LDM effects cause a modification of the net number of phonons in the lattice as compared to the standard thermal result. In addition, we estimate the contribution of LDM to the ion-ion thermal conductivity in the outer crust and find that it can be significantly enhanced at large densities. Our results imply that for magnetized neutron stars the LDM-enhanced global conductivity in the outer crust will tend to reduce the anisotropic heat conduction between perpendicular and parallel directions to the magnetic field.

  14. Neutron star equations of state with optical potential constraint

    Energy Technology Data Exchange (ETDEWEB)

    Antić, S., E-mail: S.Antic@gsi.de [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, D-64291 Darmstadt (Germany); Technische Universität Darmstadt, Schlossgartenstraße 2, D-64289 Darmstadt (Germany); Typel, S., E-mail: S.Typel@gsi.de [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, D-64291 Darmstadt (Germany)

    2015-06-15

    Nuclear matter and neutron stars are studied in the framework of an extended relativistic mean-field (RMF) model with higher-order derivative and density dependent couplings of nucleons to the meson fields. The derivative couplings lead to an energy dependence of the scalar and vector self-energies of the nucleons. It can be adjusted to be consistent with experimental results for the optical potential in nuclear matter. Several parametrization, which give identical predictions for the saturation properties of nuclear matter, are presented for different forms of the derivative coupling functions. The stellar structure of spherical, non-rotating stars is calculated for these new equations of state (EoS). A substantial softening of the EoS and a reduction of the maximum mass of neutron stars is found if the optical potential constraint is satisfied.

  15. Light dark matter scattering in outer neutron star crusts

    Science.gov (United States)

    Cermeño, Marina; Pérez-García, M. Ángeles; Silk, Joseph

    2016-09-01

    We calculate for the first time the phonon excitation rate in the outer crust of a neutron star due to scattering from light dark matter (LDM) particles gravitationally boosted into the star. We consider dark matter particles in the sub-GeV mass range scattering off a periodic array of nuclei through an effective scalar-vector interaction with nucleons. We find that LDM effects cause a modification of the net number of phonons in the lattice as compared to the standard thermal result. In addition, we estimate the contribution of LDM to the ion-ion thermal conductivity in the outer crust and find that it can be significantly enhanced at large densities. Our results imply that for magnetized neutron stars the LDM-enhanced global conductivity in the outer crust will tend to reduce the anisotropic heat conduction between perpendicular and parallel directions to the magnetic field.

  16. On the spin evolution of a proto-neutron star

    CERN Document Server

    Camelio, G; Pons, J A; Ferrari, V

    2016-01-01

    We study the evolution of the rotation rate of a proto-neutron star, born in a core-collapse supernova, in the first seconds of its life. During this phase, the star evolution can be described as a sequence of stationary configurations, which we determine by solving the neutrino transport and the stellar structure equations in general relativity. We include in our model the angular momentum loss due to neutrino emission. We find that the requirement of a rotation rate not exceeding the mass-shedding limit at the beginning of the evolution, implies a strict bound on the rotation rate at later times. Moreover, assuming that the proto-neutron star is born with a finite ellipticity, we determine the emitted gravitational wave signal, and estimate its detectability by present and future ground-based interferometric detectors.

  17. Luminosities of Disk--accreting Non--magnetic Neutron Stars

    CERN Document Server

    Thampan, A V

    2002-01-01

    Disk accretion onto a neutron star possessing a weak surface magnetic field ($B \\le 10^8$ G) provides interesting X-ray emission scenarios, and is relevant for understanding X-ray bursters and low-mass X-ray binaries (LMXBs). The standard (Newtonian) theory of disk-accretion predicts that the matter spiralling in from infinity loses one-half of its total gravitational energy in the extended disk, and the remainder in a narrow boundary layer girdling the neutron star. The ratio of the boundary layer luminosity to that from the disk ($E_{\\rm BL}/E_{\\rm D}$) is, therefore, unity. On incorporation of general relativity without rotation (Schwarzschild solution), $E_{\\rm BL}/E_{\\rm D}$ is seen to be as high as 6. We construct rotating sequences of neutron stars for three representative equations of state. We show here that for a neutron star rotating at a limit where centrifugal force balances the inward gravitational force, $E_{\\rm BL}/E_{\\rm D}\\sim 0$.

  18. Flux-Vortex Pinning and Neutron Star Evolution

    Science.gov (United States)

    Alpar, M. Ali

    2017-09-01

    G. Srinivasan et al. (1990) proposed a simple and elegant explanation for the reduction of the neutron star magnetic dipole moment during binary evolution leading to low mass X-ray binaries and eventually to millisecond pulsars: Quantized vortex lines in the neutron star core superfluid will pin against the quantized flux lines of the proton superconductor. As the neutron star spins down in the wind accretion phase of binary evolution, outward motion of vortex lines will reduce the dipole magnetic moment in proportion to the rotation rate. The presence of a toroidal array of flux lines makes this mechanism inevitable and independent of the angle between the rotation and magnetic axes. The incompressibility of the flux-line array (Abrikosov lattice) determines the epoch when the mechanism will be effective throughout the neutron star. Flux vortex pinning will not be effective during the initial young radio pulsar phase. It will, however, be effective and reduce the dipole moment in proportion with the rotation rate during the epoch of spindown by wind accretion as proposed by Srinivasan et al. The mechanism operates also in the presence of vortex creep.

  19. Stellar evolution on the borderline of white dwarf and neutron star formation

    NARCIS (Netherlands)

    Poelarends, A.J.T.

    2007-01-01

    This thesis is about the evolution of stars, specifically about the final fate of stars at the borderline between the formation of white dwarfs and neutron stars. It is well known that the mass and the metallicity are the two determining factors in stellar evolution, and for a given initial chemical

  20. General relativistic neutron stars with twisted magnetosphere

    CERN Document Server

    Pili, A G; Del Zanna, L

    2014-01-01

    Soft Gamma-Ray Repeaters and Anomalous X-Ray Pulsars are extreme manifestations of the most magnetized neutron stars: magnetars. The phenomenology of their emission and spectral properties strongly support the idea that the magnetospheres of these astrophysical objects are tightly twisted in the vicinity of the star. Previous studies on equilibrium configurations have so far focused on either the internal or the external magnetic field configuration, without considering a real coupling between the two fields. Here we investigate numerical equilibrium models of magnetized neutron stars endowed with a confined twisted magnetosphere, solving the general relativistic Grad-Shafranov equation both in the interior and in the exterior of the compact object. A comprehensive study of the parameters space is provided to investigate the effects of different current distributions on the overall magnetic field structure.

  1. The Effect of the Gravitational Mass on the Electromagnetic Radiation from an Oblique, Relativistically Rotating Dipole (Neutron Star)

    CERN Document Server

    AlMuhammad, Anwar S

    2002-01-01

    Relying on the magnetic dipole model of the pulsar, we use the extension of the work of Haxton-Ruffini [31] for single charges by DePaolis-Ingrosso-Qadir [32] for an obliquely rotating magnetic dipole, to incorporate the effect of the gravitational mass. So, by using the numerical and analytical solutions of the differential equation for the radiation, we construct the energy spectra for different masses of the dipole-NS. These spectra show that, in relatively low angular momentum l, the effect of the gravitational mass is very significant in suppressing the relativistic enhancement factor, which had been found [27, 28, 32], by two to three orders of magnitude, as the mass changes from 0.5 solar mass to 3 solar masses. It is an indication that most of the angular momentum of the NS is retained as rotational kinetic energy instead of being radiated as an electromagnetic energy. Also, the suppressing in radiation energy is more or less independent of the angular momentum, and the high rotational velocity. We al...

  2. Differences in the Cooling Behavior of Strange Quark Matter Stars and Neutron Stars

    OpenAIRE

    Schaab, Christoph; Hermann, Bernd; Weber, Fridolin; Weigel, Manfred K.

    1997-01-01

    The general statement that hypothetical strange (quark matter) stars cool more rapidly than neutron stars is investigated in greater detail. It is found that the direct Urca process could be forbidden not only in neutron stars but also in strange stars. In this case, strange stars are slowly cooling, and their surface temperatures are more or less indistinguishable from those of slowly cooling neutron stars. Furthermore the case of enhanced cooling is reinvestigated. It shows that strange sta...

  3. Black Holes and Neutron Stars in Nearby Galaxies: Insights with NuSTAR

    Science.gov (United States)

    Vulic, Neven; Hornschemeier, Ann E.; Wik, Daniel R.; Yukita, Mihoko; Ptak, Andrew; Zezas, Andreas; Lehmer, Bret

    2017-08-01

    There are a handful of diagnostics that permit determination of compact object identity in X-ray binaries (XRBs), and most of these are confined to bright Galactic sources for which a large number of photons can be gathered. We report on recent work using sensitive hard X-ray constraints to separate black holes from neutron stars in external galaxies with NuSTAR. Determining the ratio of XRBs that are black holes or neutron stars in different galactic environments reveals critical clues about the formation and evolution of binary systems. We analyze a NuSTAR-selected sample of ≈10 nearby galaxies within 5 Mpc that represent a range of star formation rates (0.1 - 10 M⊙ yr-1) and stellar masses (109-11 M⊙). Using color-color and color-intensity diagnostics we classify sources by their accretion states and compact object types. We analyze the 12-25 keV X-ray luminosity functions (XLFs) of our sample scaled by specific star formation rate and compare with the 0.5-8 keV analogues. Our diagnostic methods allow us to produce black hole-only and neutron star-only extragalactic XLFs for the first time.

  4. Hiding a neutron star inside a wormhole

    CERN Document Server

    Dzhunushaliev, Vladimir; Kleihaus, Burkhard; Kunz, Jutta

    2014-01-01

    We consider neutron-star-plus-wormhole configurations supported by a massless ghost scalar field. The neutron fluid is modeled by an anisotropic equation of state. When the central energy density of the fluid is of comparable magnitude to the one of the scalar field, configurations with an equator at the center and a double-throat arise. These double-throat wormholes can be either partially or completely filled by the neutron fluid. In the latter case, the passage of light - radiated by the neutron matter - through these wormholes is studied. A stability analysis indicates that all considered configurations are unstable with respect to linear perturbations, independent of whether the fluid is isotropic or anisotropic.

  5. Progenitor neutron stars of the lightest and heaviest millisecond pulsars

    CERN Document Server

    Fortin, M; Haensel, P; Zdunik, J L

    2014-01-01

    Recent mass measurements of two binary millisecond pulsars, PSR J1614-2230 and PSR J0751+1807 with a mass M=1.97+/-0.04 Msun and M=1.26+/-0.14 Msun respectively indicate a large span of masses for such objects, and possibly also a broad spectrum of neutron star masses born in core-collapse supernovae. Starting from a zero-age main sequence binary stage, we aim at inferring the masses of the progenitor neutron star of PSR J1614-2230 and PSR J0751+1807 by taking into account the differences in the evolutionary stages preceding their formation. Using simulations for the evolution of binary stars we reconstruct the evolutionary tracks leading to the formation of PSR J1614-2230 and PSR J0751+1807. We analyse in detail the spin evolution due to the accretion of matter from a disk in the medium-mass/low-mass X-ray binary. General relativistic effects and the damping of surface magnetic field associated with accretion are accounted for. We consider two equations of state of dense matter, one for purely nucleonic matt...

  6. Quasi-universal properties of neutron star mergers

    CERN Document Server

    Bernuzzi, Sebastiano; Balmelli, Simone; Dietrich, Tim; Ujevic, Maximiliano

    2014-01-01

    Binary neutron star mergers are investigated using nonlinear 3+1 numerical relativity simulations and the analytical effective-one-body (EOB) model. The EOB model predicts quasi-universal relations between the mass-rescaled gravitational wave frequency and the binding energy at the moment of merger, and certain dimensionless binary tidal coupling constants depending on the stars Love numbers, compactnesses and the binary mass ratio. These relations are quasi-universal in the sense that, for a given value of the tidal coupling constant, they depend significantly neither on the equation of state nor on the mass ratio, though they do depend on stars spins. The spin dependence is approximately linear for small spins aligned with the orbital angular momentum. The quasi-universality is a property of the conservative dynamics, and emerges as the binary interaction becomes tidally dominated. This analytical prediction is qualitatively consistent with new, multi-orbit numerical relativity results for the relevant case...

  7. Strangeness in nuclei and neutron stars

    Science.gov (United States)

    Lonardoni, Diego

    2017-01-01

    The presence of exotic particles in the core of neutron stars (NS) has been questioned for a long time. At present, it is still an unsolved problem that drives intense research efforts, both theoretical and experimental. The appearance of strange baryons in the inner regions of a NS, where the density can exceed several times the nuclear saturation density, is likely to happen due to energetic considerations. The onset of strange degrees of freedom is considered as an effective mechanism to soften the equation of state (EoS). This softening affects the entire structure of the star, reducing the pressure and therefore the maximum mass that the star can stably support. The observation of two very massive NS with masses of the order of 2M⊙ seems instead to rule out soft EoS, apparently excluding the possibility of hyperon formation in the core of the star. This inconsistency, usually referred to as the hyperon puzzle, is based on what we currently know about the interaction between strange particles and normal nucleons. The combination of a poor knowledge of the hypernuclear interactions and the difficulty of obtaining clear astrophysical evidence of the presence of hyperons in NS makes the understanding of the behavior of strange degrees of freedom in NS an intriguing theoretical challenge. We give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction. We attack this issue by employing a quantum Monte Carlo (QMC) technique, that has proven to be successful in the description of strongly correlated Fermion systems, to the study of finite size nuclear systems including strange degrees of freedom, i.e. hypernuclei. We show that many-body hypernuclear forces are fundamental to properly reproduce the ground state physics of Λ hypernuclei from light- to medium-heavy. However, the poor abundance of experimental data on strange nuclei leaves room for a good deal of indetermination in the construction of hypernuclear

  8. R-modes in neutron stars: Theory and observations

    CERN Document Server

    Haskell, Brynmor

    2015-01-01

    In this article I will review the theory behind the gravitational wave driven r-mode instability in rapidly rotating neutron stars and discuss which constraints can be derived from observations of spins and temperatures in Low Mass X-ray Binaries. I will discuss how a standard, `minimal' neutron star model is not consistent with the data, and discuss some of the additional physical mechanisms that could reconcile theory with observations. In particular I will focus on additional forms of damping due to exotic cores and on strong mutual friction due to superfluid vortices cutting through superconducting flux tubes, and examine the repercussions these effects could have on the saturation amplitude of the mode. Finally I will also discuss the possibility that oscillations due to r-modes may have been recently observed in the X-ray light curves of two Low Mass X-ray Binaries.

  9. Symmetry energy, unstable nuclei, and neutron star crusts

    CERN Document Server

    Iida, Kei

    2013-01-01

    Phenomenological approach to inhomogeneous nuclear matter is useful to describe fundamental properties of atomic nuclei and neutron star crusts in terms of the equation of state of uniform nuclear matter. We review a series of researches that we have developed by following this approach. We start with more than 200 equations of state that are consistent with empirical masses and charge radii of stable nuclei and then apply them to describe matter radii and masses of unstable nuclei, proton elastic scattering and total reaction cross sections off unstable nuclei, and nuclei in neutron star crusts including nuclear pasta. We finally discuss the possibility of constraining the density dependence of the symmetry energy from experiments on unstable nuclei and even observations of quasi-periodic oscillations in giant flares of soft gamma-ray repeaters.

  10. Symmetry energy, unstable nuclei and neutron star crusts

    Energy Technology Data Exchange (ETDEWEB)

    Iida, Kei [Kochi University, Department of Natural Science, Kochi (Japan); RIKEN Nishina Center, Saitama (Japan); Oyamatsu, Kazuhiro [RIKEN Nishina Center, Saitama (Japan); Aichi Shukutoku University, Department of Human Informatics, Aichi (Japan)

    2014-02-15

    The phenomenological approach to inhomogeneous nuclear matter is useful to describe fundamental properties of atomic nuclei and neutron star crusts in terms of the equation of state of uniform nuclear matter. We review a series of researches that we have developed by following this approach. We start with more than 200 equations of state that are consistent with empirical masses and charge radii of stable nuclei and then apply them to describe matter radii and masses of unstable nuclei, proton elastic scattering and total reaction cross sections off unstable nuclei, and nuclei in neutron star crusts including nuclear pasta. We finally discuss the possibility of constraining the density dependence of the symmetry energy from experiments on unstable nuclei and even observations of quasi-periodic oscillations in giant flares of soft gamma-ray repeaters. (orig.)

  11. 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.

  12. Radial oscillations of neutron stars in strong magnetic fields

    Indian Academy of Sciences (India)

    V K Gupta; Vinita Tuli; S Singh; J D Anand; Ashok Goyal

    2002-09-01

    The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.

  13. Predicting neutron star spins from twin kHz QPOs

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    We briefly review the proposed relations between the frequencies of twin kilohertz quasi-periodic oscillations(kHz QPOs) and the spin frequencies in neutron star low-mass X-ray binaries(NSLMXBs).To test the validity of the proposed models,we estimate the spin frequencies under these theoretical relations and compare them with the measured ones.It seems that magnetohydrodynamic(MHD) oscillations are more promising to account for the kHz QPOs.

  14. Quark matter nucleation in neutron stars and astrophysical implications

    Energy Technology Data Exchange (ETDEWEB)

    Bombaci, Ignazio [Universita di Pisa, Dipartimento di Fisica ' ' E. Fermi' ' , Pisa (Italy); INFN, Pisa (Italy); European Gravitational Observatory, Cascina (Italy); Logoteta, Domenico [INFN, Pisa (Italy); Vidana, Isaac; Providencia, Constanca [University of Coimbra, CFisUC, Department of Physics, Coimbra (Portugal)

    2016-03-15

    A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We investigate the quark deconfinement phase transition in cold (T = 0) and hot β-stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates an enormous amount of energy, of the order of 10{sup 53} erg, which causes a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the Universe two coexisting families of compact stars: pure hadronic stars and quark stars. We introduce the concept of critical mass M{sub cr} for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M < M{sub cr} could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars. (orig.)

  15. Quark matter nucleation in neutron stars and astrophysical implications

    Science.gov (United States)

    Bombaci, Ignazio; Logoteta, Domenico; Vidaña, Isaac; Providência, Constança

    2016-03-01

    A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We investigate the quark deconfinement phase transition in cold (T=0 and hot β -stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates an enormous amount of energy, of the order of 1053erg, which causes a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the Universe two coexisting families of compact stars: pure hadronic stars and quark stars. We introduce the concept of critical mass M_{cr} for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M < M_{cr} could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.

  16. Ways to constrain neutron star equation of state models using relativistic disc lines

    CERN Document Server

    Bhattacharyya, Sudip

    2011-01-01

    Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular orbit (ISCO). Therefore an inferred disc inner edge radius either provides the stellar radius, or can directly constrain stellar equation of state (EoS) models using the theoretically computed ISCO radius for the spacetime of a rapidly spinning neutron star. However, this procedure requires numerical computation of stellar and ISCO radii for various EoS models and neutron star configurations using an appropriate rapidly spinning stellar spacetime. We have fully general relativistically calculated about 16000 stable neutron star structures to explore and establish the above mentioned procedure, and to show that the Kerr spacetime is inadequate for this purpose. Our work systematically studies the methods to constrain Eo...

  17. Constraining the State of Ultra-dense Matter with the Neutron Star Interior Composition Explorer

    Science.gov (United States)

    Bogdanov, Slavko

    2016-04-01

    [This presentation is submitted on behalf of the entire NICER Science Team] The state of cold matter at densities exceeding those of atomic nuclei remains one of the principal outstanding problems in modern physics. Neutron stars provide the only known setting in the universe where these physical conditions can be explored. Thermal X-ray radiation from the physical surface of a neutron star can serve as a powerful tool for probing the poorly understood behavior of the matter in the dense stellar interior. For instance, realistic modeling of the thermal X-ray modulations observed from rotation-powered millisecond pulsars can produce stringent constraints on the neutron star mass-radius relation, and by extension the state of supra-nuclear matter. I will describe the prospects for precision neutron star equation of state constraints with millisecond pulsars using the forthcoming Neutron Star Interior Composition Explorer (NICER) X-ray timing mission.

  18. Analyzing Neutron Star in HESS J1731-347 from Thermal Emission and Cooling Theory

    CERN Document Server

    Ofengeim, D D; Klochkov, D; Suleimanov, V; Yakovlev, D G

    2015-01-01

    The central compact object in the supernova remnant HESS J1731-347 appears to be the hottest observed isolated cooling neutron star. The cooling theory of neutron stars enables one to explain observations of this star by assuming the presence of strong proton superfluidity in the stellar core and the existence of the surface heat blanketing envelope which almost fully consists of carbon. The cooling model of this star is elaborated to take proper account of the neutrino emission due to neutron-neutron collisions which is not suppressed by proton superfluidity. Using the results of spectral fits of observed thermal spectra for the distance of 3.2 kpc and the cooling theory for the neutron star of age 27 kyr, new constraints on the stellar mass and radius are obtained which are more stringent than those derived from the spectral fits alone.

  19. Polar kicks and the spin period - eccentricity relation in double neutron stars

    CERN Document Server

    Willems, B; Kalogera, V; Belczynski, K

    2007-01-01

    We present results of a population synthesis study aimed at examining the role of spin-kick alignment in producing a correlation between the spin period of the first-born neutron star and the orbital eccentricity of observed double neutron star binaries in the Galactic disk. We find spin-kick alignment to be compatible with the observed correlation, but not to alleviate the requirements for low kick velocities suggested in previous population synthesis studies. Our results furthermore suggest low- and high-eccentricity systems may form through two distinct formation channels distinguished by the presence or absence of a stable mass transfer phase before the formation of the second neutron star. The presence of highly eccentric systems in the observed sample of double neutron stars may furthermore support the notion that neutron stars accrete matter when moving through the envelope of a giant companion.

  20. Tidal Love numbers of neutron stars

    CERN Document Server

    Hinderer, Tanja

    2007-01-01

    For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k2. Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n~0.5-1.0. The equilibrium stellar model is obtained by numerical integration of the Tolman-Oppenheimer-Volkhov equations. We calculate the linear l=2 static perturbations to the Schwarzschild spacetime following the method of Thorne and Campolattaro. Combining the perturbed Einstein equations into a single second order differential equation for the perturbation to the metric coefficient g_tt, and matching the exterior solution to the asymptotic expansion of the metric in the star's local asymptotic rest frame gives the Love number. Our results agree well with the Newtonian results in the weak field limit. The fully relativistic values differ from the Newtonian values by up to ~24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron sta...

  1. Neutron Star Radii, Universal Relations, and the Role of Prior Distributions

    CERN Document Server

    Steiner, A W; Brown, E F

    2015-01-01

    We investigate constraints on neutron star structure arising from the assumptions that neutron stars have crusts, that recent calculations of pure neutron matter limit the equation of state of neutron star matter near the nuclear saturation density, that the high-density equation of state is limited by causality and the largest high-accuracy neutron star mass measurement, and that general relativity is the correct theory of gravity. We explore the role of prior assumptions by considering two classes of equation of state models. In a first, the intermediate- and high-density behavior of the equation of state is parameterized by piecewise polytropes. In the second class, the high-density behavior of the equation of state is parameterized by piecewise continuous line segments. The smallest density at which high-density matter appears is varied in order to allow for strong phase transitions above the nuclear saturation density. We critically examine correlations among the pressure of matter, radii, maximum masses...

  2. Superfluid Neutrons in the Core of the Neutron Star in Cassiopeia A

    CERN Document Server

    Page, Dany; Lattimer, James M; Steiner, Andrew W

    2011-01-01

    The supernova remnant Cassiopeia A contains the youngest known neutron star which is also the first one for which real time cooling has ever been observed. In order to explain the rapid cooling of this neutron star, we first present the fundamental properties of neutron stars that control their thermal evolution with emphasis on the neutrino emission processes and neutron/proton superfluidity/superconductivity. Equipped with these results, we present a scenario in which the observed cooling of the neutron star in Cassiopeia A is interpreted as being due to the recent onset of neutron superfluidity in the core of the star. The manner in which the earlier occurrence of proton superconductivity determines the observed rapidity of this neutron star's cooling is highlighted. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars.

  3. Distributions of Neutron Exposures in AGB Stars and the Galaxy

    Institute of Scientific and Technical Information of China (English)

    Wen-Yuan Cui; Feng-Hua Zhang; Wei-Juan Zhang; Lu Zhang; Bo Zhang

    2007-01-01

    Based on the s-process nucleosynthesis model with the 13C(α, n)16O reaction occurring under radiative conditions in the interpulse phases, we investigate the characteristics of the distribution of neutron exposure in low-mass Asymptotic Giant Branch (AGB) stars.We introduce a new concept, the distribution of neutron exposures of the Galaxy (NEG), to study the chemical evolution characteristics of the Galaxy for s-process elements. Using a chemical evolution model of the Galaxy, we develop a model for the NEG and obtain the evolution results of the NEG in different epochs. The present results appear to reasonably reproduce the distribution of neutron exposures of the solar system (hereafter NES). The main component and the strong component in the NES are built up in different epochs. The strong component of the s-process is mainly synthesised in the low-mass and metal-poor AGB stars,and the main component is produced by the s-process in the low-mass AGB stars with higher metallicities.

  4. Free fall onto magnetized neutron stars

    Science.gov (United States)

    Salpeter, E. E.

    Some compact X-ray sources show evidence of cyclotron line radiation from excited electron Landau orbits, powered by hydrogen and helium falling onto a neutron star atmosphere along the magnetic field. The slowing of the incident matter is discussed, including the spread in energy loss due to Coulomb scattering and direct nuclear reactions for disintegrating the α particles. The α disintegrations, followed by neutron capture, lead to nuclear γ rays; the γ-ray intensity is (indirectly) coupled to the Coulomb energy loss and the cyclotron line emission.

  5. Slowly rotating superfluid neutron stars with isospin dependent entrainment in a two-fluid model

    CERN Document Server

    Kheto, Apurba

    2015-01-01

    We investigate the slowly rotating general relativistic superfluid neutron stars including the entrainment effect in a two-fluid model, where one fluid represents the superfluid neutrons and the other is the charge-neutral fluid called the proton fluid, made of protons and electrons. The equation of state and the entrainment effect between the superfluid neutrons and the proton fluid are computed using a relativistic mean field (RMF) model where baryon-baryon interaction is mediated by the exchange of $\\sigma$, $\\omega$, and $\\rho$ mesons and scalar self interactions are also included. The equations governing rotating neutron stars in the slow rotation approximation are second order in rotational velocities of neutron and proton fluids. We explore the effects of the isospin dependent entrainment and the relative rotation between two fluids on the global properties of rotating superfluid neutron stars such as mass, shape, and the mass shedding (Kepler) limit within the RMF model with different parameter sets. ...

  6. Rapidly Rotating Neutron Stars in Dilatonic Einstein-Gauss-Bonnet Theory

    CERN Document Server

    Kleihaus, Burkhard; Mojica, Sindy; Zagermann, Marco

    2016-01-01

    We construct sequences of rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory, employing two equations of state for the nuclear matter. We analyze the dependence of the physical properties of these neutron stars on the Gauss-Bonnet coupling strength. For a given equation of state we determine the physically relevant domain of rapidly rotating neutron stars, which is delimited by the set of neutron stars rotating at the Kepler limit, the set of neutron stars along the secular instability line, and the set of static neutron stars. As compared to Einstein gravity, the presence of the Gauss-Bonnet term decreases this domain, leading to lower values for the maximum mass as well as to smaller central densities. The quadrupole moment is decreased by the Gauss-Bonnet term for rapidly rotating neutron stars, while it is increased for slowly rotating neutron stars. The universal relation between the quadrupole moment and the moment of inertia found in General Relativity appears to extend to dilaton...

  7. Deformed neutron stars due to strong magnetic field in terms of relativistic mean field theories

    Science.gov (United States)

    Yanase, Kota; Yoshinaga, Naotaka

    2014-09-01

    Some observations suggest that magnetic field intensity of neutron stars that have particularly strong magnetic field, magnetars, reaches values up to 1014-15G. It is expected that there exists more strong magnetic field of several orders of magnitude in the interior of such stars. Neutron star matter is so affected by magnetic fields caused by intrinsic magnetic moments and electric charges of baryons that masses of neutron stars calculated by using Tolman-Oppenheimer-Volkoff equation is therefore modified. We calculate equation of state (EOS) in density-dependent magnetic field by using sigma-omega-rho model that can reproduce properties of stable nuclear matter in laboratory Furthermore we calculate modified masses of deformed neutron stars.

  8. Measuring surface temperature of isolated neutron stars and related problems

    Science.gov (United States)

    Teter, Marcus Alton

    New and exciting results for measuring neutron star surface temperatures began with the successful launch of the Chandra X-ray observatory. Among these results are new detections of neutron star surface temperatures which have made it possible to seriously test neutron star thermal evolution theories. The important new temperature determination of the Vela pulsar (Pavlov, et al., 2001a) requires a non-standard cooling scenario to explain it. Apart from this result, we have measured PSR B1055-52's surface temperature in this thesis, determining that it can be explained by standard cooling with heating. Our spectral fit of the combined data from ROSAT and Chandra have shown that a three component model, two thermal blackbodies and an non-thermal power-law, is required to explain the data. Furthermore, our phase resolved spectroscopy has begun to shed light on the geometry of the hot spot on PSR B1055-52's surface as well as the structure of the magnetospheric radiation. Also, there is strong evidence for a thermal distribution over its surface. Most importantly, the fact that PSR B1055-52 does not have a hydrogen atmosphere has been firmly established. To reconcile these two key observations, on the Vela pulsar and PSR B1055-52, we tested neutron star cooling with neutrino processes including the Cooper pair neutrino emission process. Overall, it has been found that a phase change associated with pions being present in the cores of more massive neutron stars explains all current of the data. A transition from neutron matter to pion condensates in the central stellar core explains the difference between standard and non-standard cooling scenarios, because the superfluid suppression of pion cooling will reduce the emissivity of the pion direct URCA process substantially. A neutron star with a mass of [Special characters omitted.] with a medium stiffness equation of state and a T72 type neutron superfluid models the standard cooling case well. A neutron star of [Special

  9. Neutron stars in Horndeski gravity

    Science.gov (United States)

    Maselli, Andrea; Silva, Hector O.; Minamitsuji, Masato; Berti, Emanuele

    2016-06-01

    Horndeski's theory of gravity is the most general scalar-tensor theory with a single scalar whose equations of motion contain at most second-order derivatives. A subsector of Horndeski's theory known as "Fab Four" gravity allows for dynamical self-tuning of the quantum vacuum energy, and therefore it has received particular attention in cosmology as a possible alternative to the Λ CDM model. Here we study compact stars in Fab Four gravity, which includes as special cases general relativity ("George"), Einstein-dilaton-Gauss-Bonnet gravity ("Ringo"), theories with a nonminimal coupling with the Einstein tensor ("John"), and theories involving the double-dual of the Riemann tensor ("Paul"). We generalize and extend previous results in theories of the John class and were not able to find realistic compact stars in theories involving the Paul class.

  10. High-mass X-ray binaries and OB runaway stars

    NARCIS (Netherlands)

    Kaper, L.; van der Meer, A.; Tijani, A.H.; Allen, C.; Scarfe, C.

    2004-01-01

    High-mass X-ray binaries (HMXBs) represent an important phase in the evolution of massive binary systems and provide fundamental information on the properties of the OB-star primaries and their compact secondaries (neutron star, black hole). Recent observations indicate that the neutron stars in som

  11. Modeling magnetized neutron stars using resistive MHD

    CERN Document Server

    Palenzuela, Carlos

    2013-01-01

    This work presents an implementation of the resistive MHD equations for a generic algebraic Ohm's law which includes the effects of finite resistivity within full General Relativity. The implementation naturally accounts for magnetic-field-induced anisotropies and, by adopting a phenomenological current, is able to accurately describe electromagnetic fields in the star and in its magnetosphere. We illustrate the application of this approach in interesting systems with astrophysical implications; the aligned rotator solution and the collapse of a magnetized rotating neutron star to a black hole.

  12. Role of magnetic interactions in neutron stars

    Directory of Open Access Journals (Sweden)

    Adhya Souvik Priyam

    2015-01-01

    Full Text Available In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case.

  13. Why neutron stars have three hairs

    Science.gov (United States)

    Stein, Leo; Yagi, Kent; Pappas, George; Yunes, Nicolas; Apostolatos, Theocharis

    2015-04-01

    Neutron stars have recently been found to enjoy a certain `baldness' in their multipolar structure which is independent of the equation of state (EoS) of dense nuclear matter. This is reminiscent of the black hole no-hair relations, and in stark contrast to regular stars. Why is this? Is it because realistic EoSs are sufficiently similar, or because GR effects are especially important, or because the nuclear matter is `cold'? We explore the physics behind these and more hypotheses, and give a convincing explanation for the true origin of the three-hair relations.

  14. The Deconfinement Phase Transition in the Interior of Neutron Stars

    CERN Document Server

    Zhou, Xia

    2010-01-01

    The decon?nement phase transition which happens in the interior of neutron stars are investigated. Coupled with the spin evolution of the stars, the effect of entropy production and deconfinement heat generation during the deconfinement phase transition in the mixed phase of the neutron stars are discussed. The entropy production of deconfinement phase transition can be act as a signature of phase transition, but less important and does not significantly change the thermal evolution of neutron stars. The deconfinement heat can change the thermal evolution of neutron star distinctly.

  15. Electromagnetic multipole fields of neutron stars

    Science.gov (United States)

    Roberts, W. J.

    1979-01-01

    A formalism is developed for treating general multipole electromagnetic fields of neutron stars. The electric multipoles induced in a neutron star by its rotation with an arbitrary magnetic multipole at its center are presented. It is shown how to express a family of off-centered multipoles having the same l weight as an infinite array of centered multipoles of increasing l weight referred to the rotational axis. General expressions are given for the linear momentum present in the superposition of arbitrary multipole fields, and the results are combined to compute the radiation rate of linear momentum by an off-centered dipole to zeroth order in the parameter Omega x R/c. The general Deutsch (1955) solution is then rederived in a clear consistent manner, and some minor additions and corrections are provided.

  16. Life extinctions by neutron star mergers

    CERN Document Server

    Dar, Arnon; Shaviv, N J; Dar, Arnon; Laor, Ari; Shaviv, Nir J.

    1997-01-01

    High energy cosmic ray jets from nearby mergers or accretion induced collapse (AIC) of neutron stars (NS) that hit the atmosphere can produce lethal fluxes of atmospheric muons at ground level, underground and underwater, destroy the ozone layer and radioactivate the environment. They could have caused most of the massive life extinctions on planet Earth in the past 600 My. Biological mutations due to ionizing radiations could have caused the fast appearance of new species after the massive extinctions. An early warning of future extinctions due to NS mergers may be obtained by identifying, mapping and timing all the nearby binary neutron stars systems. A warning of an approaching cosmic ray burst from a nearby NS merger/AIC may be provided by a very intense gamma ray burst which preceeds it.

  17. Nuclear pasta in supernovae and neutron stars

    CERN Document Server

    Watanabe, Gentaro

    2011-01-01

    In supernova cores and neutron star crusts, nuclei with exotic shapes such as rod-like and slab-like nuclei are expected to exist. These nuclei are collectively called nuclear "pasta". For the past decades, existence of the pasta phases in the equilibrium state has been studied using various methods. Recently, the formation process of the pasta phases, which has been a long-standing problem, has been unveiled using molecular dynamics simulations. In this review, we first provide the astrophysical background of supernovae and neutron stars and overview the history of the study of the pasta phases. We then focus on the recent study on the formation process of the pasta phases. Finally, we discuss future important issues related to the pasta phases: their astrophysical evidence and consequences.

  18. Thermal radiation from magnetic neutron star surfaces

    CERN Document Server

    Pérez-Azorin, J F; Pons, J A

    2005-01-01

    We investigate the thermal emission from magnetic neutron star surfaces in which the cohesive effects of the magnetic field have produced the condensation of the atmosphere and the external layers. This may happen for sufficiently cool atmospheres with moderately intense magnetic fields. The thermal emission from an isothermal bare surface of a neutron star shows no remarkable spectral features, but it is significantly depressed at energies below some threshold energy. However, since the thermal conductivity is very different in the normal and parallel directions to the magnetic field lines, the presence of the magnetic field is expected to produce a highly anisotropic temperature distribution, depending on the magnetic field geometry. In this case, the observed flux of such an object looks very similar to a BB spectrum, but depressed in a nearly constant factor at all energies. This results in a systematic underestimation of the area of the emitter (and therefore its size) by a factor 5-10 (2-3).

  19. Dissipation in relativistic superfluid neutron stars

    CERN Document Server

    Gusakov, M E; Chugunov, A I; Gualtieri, L

    2012-01-01

    We analyze damping of oscillations of general relativistic superfluid neutron stars. To this aim we extend the method of decoupling of superfluid and normal oscillation modes first suggested in [Gusakov & Kantor PRD 83, 081304(R) (2011)]. All calculations are made self-consistently within the finite temperature superfluid hydrodynamics. The general analytic formulas are derived for damping times due to the shear and bulk viscosities. These formulas describe both normal and superfluid neutron stars and are valid for oscillation modes of arbitrary multipolarity. We show that: (i) use of the ordinary one-fluid hydrodynamics is a good approximation, for most of the stellar temperatures, if one is interested in calculation of the damping times of normal f-modes; (ii) for radial and p-modes such an approximation is poor; (iii) the temperature dependence of damping times undergoes a set of rapid changes associated with resonance coupling of neighboring oscillation modes. The latter effect can substantially accel...

  20. FAST FOSSIL ROTATION OF NEUTRON STAR CORES

    Energy Technology Data Exchange (ETDEWEB)

    Melatos, A., E-mail: amelatos@unimelb.edu.au [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia)

    2012-12-10

    It is argued that the superfluid core of a neutron star super-rotates relative to the crust, because stratification prevents the core from responding to the electromagnetic braking torque, until the relevant dissipative (viscous or Eddington-Sweet) timescale, which can exceed {approx}10{sup 3} yr and is much longer than the Ekman timescale, has elapsed. Hence, in some young pulsars, the rotation of the core today is a fossil record of its rotation at birth, provided that magnetic crust-core coupling is inhibited, e.g., by buoyancy, field-line topology, or the presence of uncondensed neutral components in the superfluid. Persistent core super-rotation alters our picture of neutron stars in several ways, allowing for magnetic field generation by ongoing dynamo action and enhanced gravitational wave emission from hydrodynamic instabilities.

  1. A dynamical description of neutron star crusts

    CERN Document Server

    de la Mota, V; Eudes, Ph

    2012-01-01

    Neutron Stars are natural laboratories where fundamental properties of matter under extreme conditions can be explored. Modern nuclear physics input as well as many-body theories are valuable tools which may allow us to improve our understanding of the physics of those compact objects. In this work the occurrence of exotic structures in the outermost layers of neutron stars is investigated within the framework of a microscopic model. In this approach the nucleonic dynamics is described by a time-dependent mean field approach at around zero temperature. Starting from an initial crystalline lattice of nuclei at subnuclear densities the system evolves toward a manifold of self-organized structures with different shapes and similar energies. These structures are studied in terms of a phase diagram in density and the corresponding sensitivity to the isospin-dependent part of the equation of state and to the isotopic composition is investigated.

  2. The Fascinating World of Neutron Stars

    Science.gov (United States)

    Piekarewicz, J.

    2009-07-01

    Understanding the equation of state (EOS) of cold nuclear matter, namely, the relation between pressure and energy density, is a central goal of nuclear physics that cuts across a variety of disciplines. Indeed, the limits of nuclear existence, the collision of heavy ions, the structure of neutron stars, and the dynamics of core-collapse supernova, all depend critically on the equation of state of hadronic matter. In this contribution I will concentrate on the EOS of cold baryonic matter with special emphasis on its impact on the structure and dynamics of neutron stars. In particular, I will discuss the many fascinating phases that one encounters in the journey from the low-density crust to the high-density core.

  3. Spectroscopic Analysis of Subluminous B Stars in Binaries - Four Candidate Systems with Neutron Star/Black Hole Companions Discovered

    CERN Document Server

    Geier, S; Edelmann, H; Heber, U; Napiwotzki, R

    2006-01-01

    The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close binary systems with unseen compact companions to derive their masses and clarify their nature. Radial velocity curves were obtained from time resolved spectroscopy. The atmospheric parameters were determined in a quantitative spectral analysis. With high resolution spectra we were able to measure the projected rotational velocity of the stars with high accuracy. The assumption of orbital synchronization made it possible to constrain inclination angle and companion mass of the binaries. Five invisible companions have masses that are compatible with white dwarfs or late type main sequence stars. But four sdBs have very massive companions like heavy white dwarfs, neutron stars or even black holes. Such a high fraction of massive compact companions can not be explained with current models of binary...

  4. The Fate of Neutron Star Binary Mergers

    Science.gov (United States)

    Piro, Anthony L.; Giacomazzo, Bruno; Perna, Rosalba

    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.

  5. Disk reflection and a possible disk wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    CERN Document Server

    Degenaar, N; Parker, M; Miller-Jones, J C A; Miller, J M; Heinke, C O; Wijnands, R; Ludlam, R; Parikh, A; Hessels, J W T; Gusinskaia, N; Deller, A T; Fabian, A C

    2016-01-01

    1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present Nustar, Swift, and Chandra observations obtained around the peak of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of Lx~(2-3)E37 (D/5.8 kpc)^2 erg cm-2 (0.5-10 keV). The Nustar data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disk is viewed at an inclination of i~27-35 degrees and extended close to the neutron star, down to Rin~5-7.5 gravitational radii (~11-17 km). This inner disk radius suggests that the neutron star magnetic field strength is B<2E8 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ~7.64 keV with a significance of ~4.8 sigma. This feature could correspond to blue-shifted Fe xxvi and arise from an accretion disk wind, which would imply an outflow velocity of v~0.086c (~25800...

  6. Topological characterization of neutron star crusts

    CERN Document Server

    Dorso, C O; López, J A

    2012-01-01

    Neutron star crusts are studied using a classical molecular dynamics model developed for heavy ion reactions. After the model is shown to produce a plethora of the so-called "pasta" shapes, a series of techniques borrowed from nuclear physics, condensed matter physics and topology are used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

  7. Testing the relativistic precession model using low-frequency and kHz quasi-periodic oscillations in neutron star low-mass X-ray binaries with known spin

    Science.gov (United States)

    van Doesburgh, Marieke; van der Klis, Michiel

    2017-03-01

    We analyse all available RXTE data on a sample of 13 low-mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency νLT of a test-particle orbit whose orbital frequency is the upper kHz QPO frequency νu. Contrary to the most prominent previous studies, we find two different oscillations in the range predicted for νLT that are simultaneously present over a wide range of νu. Additionally, one of the low-frequency noise components evolves into a (third) QPO in the νLT range when νu exceeds 600 Hz. The frequencies of these QPOs all correlate to νu following power laws with indices between 0.4 and 3.3, significantly exceeding the predicted value of 2.0 in 80 per cent of the cases (at 3 to >20σ). Also, there is no evidence that the neutron star spin frequency affects any of these three QPO frequencies, as would be expected for frame dragging. Finally, the observed QPO frequencies tend to be higher than the νLT predicted for reasonable neutron star specific moment of inertia. In the light of recent successes of precession models in black holes, we briefly discuss ways in which such precession can occur in neutron stars at frequencies different from test-particle values and consistent with those observed. A precessing torus geometry and other torques than frame dragging may allow precession to produce the observed frequency correlations, but can only explain one of the three QPOs in the νLT range.

  8. Magnetars: neutron stars with huge magnetic storms

    CERN Document Server

    Rea, Nanda

    2012-01-01

    Among the many different classes of stellar objects, neutron stars provide a unique environment where we can test (at the same time) our understanding of matter with extreme density, temperature, and magnetic field. In particular, the properties of matter under the influence of magnetic fields and the role of electromagnetism in physical processes are key areas of research in physics. However, despite decades of research, our limited knowledge on the physics of strong magnetic fields is clear: we only need to note that the strongest steady magnetic field achieved in terrestrial labs is some millions of Gauss, only thousands of times stronger than a common refrigerator magnet. In this general context, I will review here the state of the art of our research on the most magnetic objects in the Universe, a small sample of neutron stars called magnetars. The study of the large high-energy emission, and the flares from these strongly magnetized (~10^{15} Gauss) neutron stars is providing crucial information about t...

  9. Magneto--thermal evolution of neutron stars

    CERN Document Server

    Pons, J A; Geppert, U

    2008-01-01

    We study the mutual influence of thermal and magnetic evolution in a neutron star's crust in axial symmetry. Taking into account realistic microphysical inputs, we find the heat released by Joule effect consistent with the circulation of currents in the crust, and we incorporate its effects in 2D cooling calculations. We solve the induction equation numerically using a hybrid method (spectral in angles, but a finite--differences scheme in the radial direction), coupled to the thermal diffusion equation. We present the first long term 2D simulations of the coupled magneto-thermal evolution of neutron stars. This substantially improves previous works in which a very crude approximation in at least one of the parts (thermal or magnetic diffusion) has been adopted. Our results show that the feedback between Joule heating and magnetic diffusion is strong, resulting in a faster dissipation of the stronger fields during the first million years of a NS's life. As a consequence, all neutron stars born with fields larg...

  10. Neutron stars interiors: Theory and reality

    Science.gov (United States)

    Stone, J. R.

    2016-03-01

    There are many fascinating processes in the universe which we observe in more detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in a core-collapse supernova explosion, one of the most violent events in the universe. As a result, the densest objects in the universe, neutron stars and/or black holes, are created. The physical basis of these events should be understood in line with observation. Unfortunately, available data do not provide adequate constraints for many theoretical models of dense matter. One of the most open areas of research is the composition of matter in the cores of neutron stars. Unambiguous fingerprints for the appearance and evolution of particular components, such as strange baryons and mesons, with increasing density, have not been identified. In particular, the hadron-quark phase transition remains a subject of intensive research. In this contribution we briefly survey the most promising observational and theoretical directions leading to progress in understanding high density matter in neutron stars. A possible way forward in modeling high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model makes connection between hadronic structure and the underlying quark make-up. It offers a natural explanation for the saturation of nuclear force and treats high-density matter, containing the full baryon octet, in terms of four uniquely defined parameters adjusted to properties of symmetric nuclear matter at saturation.

  11. Neutron stars interiors: Theory and reality

    Energy Technology Data Exchange (ETDEWEB)

    Stone, J.R. [University of Oxford, Department of Physics, Oxford (United Kingdom); University of Tennessee, Department of Physics and Astronomy, Knoxville, TN (United States)

    2016-03-15

    There are many fascinating processes in the universe which we observe in more detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in a core-collapse supernova explosion, one of the most violent events in the universe. As a result, the densest objects in the universe, neutron stars and/or black holes, are created. The physical basis of these events should be understood in line with observation. Unfortunately, available data do not provide adequate constraints for many theoretical models of dense matter. One of the most open areas of research is the composition of matter in the cores of neutron stars. Unambiguous fingerprints for the appearance and evolution of particular components, such as strange baryons and mesons, with increasing density, have not been identified. In particular, the hadron-quark phase transition remains a subject of intensive research. In this contribution we briefly survey the most promising observational and theoretical directions leading to progress in understanding high density matter in neutron stars. A possible way forward in modeling high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model makes connection between hadronic structure and the underlying quark make-up. It offers a natural explanation for the saturation of nuclear force and treats high-density matter, containing the full baryon octet, in terms of four uniquely defined parameters adjusted to properties of symmetric nuclear matter at saturation. (orig.)

  12. Dense baryonic matter: constraints from recent neutron star observations

    CERN Document Server

    Hell, Thomas

    2014-01-01

    Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of two-solar-mass neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density in order to satisfy these new constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless addition...

  13. Quiescent thermal emission from neutron stars in LMXBs

    CERN Document Server

    Turlione, Anabela; Pons, José A

    2013-01-01

    The quiescent thermal emission from neutron stars in low mass X-ray binaries after active periods of intense activity in x-rays (outbursts) has been monitored. The theoretical modeling of the thermal relaxation of the neutron star crust may be used to establish constraints on the crust and envelope composition and transport properties, depending on the astrophysical scenarios assumed. We perform numerical simulations of the neutron star crust thermal evolution and compare them with inferred surface temperatures for five sources: MXB 1659-29, KS 1731-260, EXO 0748-676, XTE J1701-462 and IGR J17480-2446. We also present stationary envelope models to be used as a boundary condition for the crustal cooling models. We obtain a relation between the mass accretion rate and the temperature reached at the crust-envelope interface at the end of the active phase that accounts for early observations and reduces the number of free parameters of the problem. With this relation we are also able to set constraints to the env...

  14. Neutron stars in Scalar-Tensor-Vector Gravity

    Science.gov (United States)

    Lopez Armengol, Federico G.; Romero, Gustavo E.

    2017-02-01

    Scalar-Tensor-Vector Gravity (STVG), also referred as Modified Gravity (MOG), is an alternative theory of the gravitational interaction. Its weak field approximation has been successfully used to describe Solar System observations, galaxy rotation curves, dynamics of clusters of galaxies, and cosmological data, without the imposition of dark components. The theory was formulated by John Moffat in 2006. In this work, we derive matter-sourced solutions of STVG and construct neutron star models. We aim at exploring STVG predictions about stellar structure in the strong gravity regime. Specifically, we represent spacetime with a static, spherically symmetric manifold, and model the stellar matter content with a perfect fluid energy-momentum tensor. We then derive the modified Tolman-Oppenheimer-Volkoff equation in STVG and integrate it for different equations of state. We find that STVG allows heavier neutron stars than General Relativity (GR). Maximum masses depend on a normalized parameter that quantifies the deviation from GR. The theory exhibits unusual predictions for extreme values of this parameter. We conclude that STVG admits suitable spherically symmetric solutions with matter sources, relevant for stellar structure. Since recent determinations of neutron stars masses violate some GR predictions, STVG appears as a viable candidate for a new gravity theory.

  15. An XMM-Newton and NuSTAR Study of IGR J18214-1318: A Non-pulsating High-mass X-Ray Binary with a Neutron Star

    Science.gov (United States)

    Fornasini, Francesca M.; Tomsick, John A.; Bachetti, Matteo; Krivonos, Roman A.; Fürst, Felix; Natalucci, Lorenzo; Pottschmidt, Katja; Wilms, Jörn

    2017-05-01

    IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-103 s). Although the lack of pulsations prevents us from definitively identifying the compact object in IGR J18214-1318, the presence of an exponential cutoff with e-folding energy ≲ 30 {keV} in its 0.3-79 keV spectrum strongly suggests that the compact object is an NS. The X-ray spectrum also shows a Fe Kα emission line and a soft excess, which can be accounted for by either a partial-covering absorber with {N}{{H}}≈ {10}23 cm-2, which could be due to the inhomogeneous supergiant wind, or a blackbody component with {kT}={1.74}-0.05+0.04 keV and {R}{BB}≈ 0.3 km, which may originate from NS hot spots. Although neither explanation for the soft excess can be excluded, the former is more consistent with the properties observed in other supergiant HMXBs. We compare IGR J18214-1318 to other HMXBs that lack pulsations or have long pulsation periods beyond the range covered by our observations.

  16. General Relativistic Simulations of Magnetized Binary Neutron Stars

    Science.gov (United States)

    Giacomazzo, Bruno

    2011-04-01

    Binary neutron stars are among the most important sources of gravitational waves which are expected to be detected by the current or next generation of gravitational wave detectors, such as LIGO and Virgo, and they are also thought to be at the origin of very important astrophysical phenomena, such as short gamma-ray bursts. I will report on some recent results obtained using the fully general relativistic magnetohydrodynamic code Whisky in simulating equal-mass binary neutron star systems during the last phases of inspiral, merger and collapse to black hole surrounded by a torus. I will in particular describe how magnetic fields can affect the gravitational wave signal emitted by these sources and their possible role in powering short gamma-ray bursts.

  17. Neutron stars in Scalar-Tensor-Vector Gravity

    CERN Document Server

    Armengol, Federico G Lopez

    2016-01-01

    Scalar-Tensor-Vector Gravity (STVG), also referred as MOdified Gravity (MOG), is an alternative theory of the gravitational interaction. Its weak field approximation has been successfully used to described Solar System observations, galaxy rotation curves, dynamics of clusters of galaxies, and cosmological data, without the imposition of dark components. The theory was formulated by John Moffat in 2006. In this work, we derive matter-sourced solutions of STVG and construct neutron star models. We aim at exploring STVG predictions about stellar structure in the strong gravity regime. Specifically, we represent spacetime with a static, spherically symmetric manifold, and model the stellar matter content with a perfect fluid energy-momentum tensor. We then derive the modified Tolman-Oppenheimer-Volkoff equation in STVG and integrate it for different equations of state. We find that STVG allows heavier neutron stars than General Relativity (GR). Maximum masses depend on a normalized parameter that quantifies the ...

  18. Gravitational waves from rotating proto-neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, V [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy); Gualtieri, L [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy); Pons, J A [Departament d' Astronomia i AstrofIsica, Universitat de Valencia, 46100 Burjassot, Valencia (Spain); Stavridis, A [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy)

    2004-03-07

    We study the effects of rotation on the quasi-normal modes (QNMs) of a newly born proto-neutron star (PNS) at different evolutionary stages, until it becomes a cold neutron star (NS). We use the Cowling approximation, neglecting spacetime perturbations, and consider different models of evolving PNS. The frequencies of the modes of a PNS are considerably lower than those of a cold NS, and are further lowered by rotation; consequently, if QNMs were excited in a sufficiently energetic process, they would radiate waves that could be more easily detectable by resonant-mass and interferometric detectors than those emitted by a cold NS. We find that for high rotation rates, some of the g-modes become unstable via the CFS instability; however, this instability is likely to be suppressed by competing mechanisms before emitting a significant amount of gravitational waves.

  19. 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.

  20. Astrophysical Constraints on Dense Matter in Neutron Stars

    CERN Document Server

    Miller, M Coleman

    2013-01-01

    Ever since the discovery of neutron stars it has been realized that they serve as probes of a physical regime that cannot be accessed in laboratories: strongly degenerate matter at several times nuclear saturation density. Existing nuclear theories diverge widely in their predictions about such matter. It could be that the matter is primarily nucleons, but it is also possible that exotic species such as hyperons, free quarks, condensates, or strange matter may dominate this regime. Astronomical observations of cold high-density matter are necessarily indirect, which means that we must rely on measurements of quantities such as the masses and radii of neutron stars and their surface effective temperatures as a function of age. Here we review the current status of constraints from various methods and the prospects for future improvements.

  1. Systematic parameter errors in inspiraling neutron star binaries

    CERN Document Server

    Favata, Marc

    2013-01-01

    The coalescence of two neutron stars is an important gravitational wave source for LIGO and other ground-based detectors. Numerous studies have considered the precision with which binary parameters (masses, spins, Love numbers) can be measured. Here I consider the accuracy with which these parameters can be determined in the presence of systematic errors due to waveform approximations. These approximations include truncation of the post-Newtonian (PN) series and neglect of neutron star (NS) spin, tidal deformation, or orbital eccentricity. All of these effects can yield systematic errors that exceed statistical errors for plausible parameter values. In particular, neglecting 4PN and higher-order terms causes a significant bias in the NS Love number. Tidal effects will not be measurable with PN inspiral waveforms if these systematic errors are not controlled.

  2. Neutron star properties and the equation of state for the core

    Science.gov (United States)

    Zdunik, J. L.; Fortin, M.; Haensel, P.

    2017-03-01

    Context. Few unified equations of state for neutron star matter, in which core and crust are described using the same nuclear model, are available. However the use of non-unified equations of state with simplified matching between the crust and core has been shown to introduce uncertainties in the radius determination, which can be larger than the expected precision of the next generation of X-ray satellites. Aims: We aim to eliminate the dependence of the radius and mass of neutron stars on the detailed model for the crust and on the crust-core matching procedure. Methods: We solved the approximate equations of the hydrostatic equilibrium for the crust of neutron stars and obtained a precise formula for the radius that only depends on the core mass and radius, the baryon chemical potential at the core-crust interface, and at the crust surface. For a fully accreted crust one needs, additionally, the value of the total deep crustal heating per one accreted nucleon. Results: For typical neutron star masses, the approximate approach allows us to determine the neutron star radius with an error 0.1% ( 10 m, equivalent to a 1% inaccuracy in the crust thickness). The formalism applies to neutron stars with a catalyzed or a fully accreted crust. The difference in the neutron star radius between the two models is proportional to the total energy release due to deep crustal heating. Conclusions: For a given model of dense matter describing the neutron star core, the radius of a neutron star can be accurately determined independent of the crust model with a precision much better than the 5% precision expected from the next generation of X-ray satellites. This allows us to circumvent the problem of the radius uncertainty that may arise when non-unified equations of state for the crust and core are used.

  3. Can very compact and very massive neutron stars both exist?

    CERN Document Server

    Drago, Alessandro; Pagliara, Giuseppe

    2013-01-01

    The existence of neutron stars with masses of $\\sim 2\\,M_{\\odot}$ requires a stiff equation of state at high densities. On the other hand, the necessary appearance also at high densities of new degrees of freedom, such as hyperons and $\\Delta$ resonances, can lead to a strong softening of the equation of state with resulting maximum masses of $\\sim 1.5\\, M_{\\odot}$ and radii smaller than $\\sim 10$ km. Hints for the existence of compact stellar objects with very small radii have been found in recent statistical analysis of quiescent low-mass X-ray binaries in globular clusters. We propose an interpretation of these two apparently contradicting measurements, large masses and small radii, in terms of two separate families of compact stars: hadronic stars, whose equation of state is soft, can be very compact, while quark stars, whose equation of state is stiff, can be very massive. In this respect an early appearance of $\\Delta$ resonances is crucial to guarantee the stability of the branch of hadronic stars. Our...

  4. Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    Science.gov (United States)

    Degenaar, N.; Altamirano, D.; Parker, M.; Miller-Jones, J. C. A.; Miller, J. M.; Heinke, C. O.; Wijnands, R.; Ludlam, R.; Parikh, A.; Hessels, J. W. T.; Gusinskaia, N.; Deller, A. T.; Fabian, A. C.

    2016-10-01

    1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present NuSTAR, Swift, and Chandra observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of LX ≃ (2-3) × 1037(D/5.8 kpc)2 erg s-1 (0.5-10 keV). The NuSTAR data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disc is viewed at an inclination of i ≃ 27°-35° and extended close to the neutron star, down to Rin ≃ 5-7.5 gravitational radii (≃11-17 km). This inner disc radius suggests that the neutron star magnetic field strength is B ≲ 2 × 108 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ≃7.64 keV with a significance of ≃4.8σ. This feature could correspond to blueshifted Fe XXVI and arise from an accretion disc wind, which would imply an outflow velocity of vout ≃ 0.086c (≃25 800 km s-1). However, this would be extreme for an X-ray binary and it is unclear if a disc wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9-342058 are consistent with a relatively small (Porb ≲ 3 h) binary orbit.

  5. Light curves from rapidly rotating neutron stars

    CERN Document Server

    Numata, Kazutoshi

    2010-01-01

    We calculate light curves produced by a hot spot of a rapidly rotating neutron star, assuming that the spot is perturbed by a core $r$-mode, which is destabilized by emitting gravitational waves. To calculate light curves, we take account of relativistic effects such as the Doppler boost due to the rapid rotation and light bending assuming the Schwarzschild metric around the neutron star. We assume that the core $r$-modes penetrate to the surface fluid ocean to have sufficiently large amplitudes to disturb the spot. For a $l'=m$ core $r$-mode, the oscillation frequency $\\omega\\approx2m\\Omega/[l'(l'+1)]$ defined in the co-rotating frame of the star will be detected by a distant observer, where $l'$ and $m$ are respectively the spherical harmonic degree and the azimuthal wave number of the mode, and $\\Omega$ is the spin frequency of the star. In a linear theory of oscillation, using a parameter $A$ we parametrize the mode amplitudes such that ${\\rm max}\\left(|\\xi_\\theta|,|\\xi_\\phi|\\right)/R=A$ at the surface, w...

  6. Is XTE J1739-285 a quark star masquerading as a neutron star

    CERN Document Server

    Xiaoping, Zheng; Li, Zhang

    2007-01-01

    The recent discovery of burst oscillation at 1122Hz in the X-ray transient XTE J1739-285 supports the suggestion that it contains a submillisecond pulsar\\cite{1}. We here find for the first time the enormous dissipation effect in the transition boundary layer between quark matter core and hadron matter envelope. Just combining the estimation with previous dissipation mechanism together, we show that XTE J1739-285 can be uniquely restricted to a quark star masquerading as a neutron star (hybrid star) that contains a pure quark matter or mixed quark-hadron matter core from synthesizing both gravitational wave radiation (r-mode) instability and Keplerian motion constraints at 1122Hz lever. Such constraints allow the radii in the range $9{\\rm km}\\leq R\\leq 12{\\rm km}$ and the masses in the range $1.2M_\\odot\\leq M\\leq 2.0M_\\odot$. The normal neutron stars, hyperon stars and strange stars within the mass-radius limits are excluded.

  7. Evolution of Close Neutron Star Binaries

    CERN Document Server

    Ogawaguchi, W

    1996-01-01

    We have calculated evolution of neutron star binaries towards the coalescence driven by gravitational radiation. The hydrodynamical effects as well as the general relativistic effects are important in the final phase. All corrections up to post$^{2.5}$-Newtonian order and the tidal effect are included in the orbital motion. The star is approximated by a simple Newtonian stellar model called affine star model. Stellar spins and angular momentum are assumed to be aligned. We have showed how the internal stellar structure affects the stellar deformation, variations of the spins, and the orbital motion of the binary just before the contact. The gravitational wave forms from the last a few revolutions significantly depend on the stellar structure.

  8. Neutron Stars and Black Holes in Star Clusters

    CERN Document Server

    Rasio, F A; Corongiu, A; D'Antona, F; Fabbiano, G; Fregeau, J M; Gebhardt, K; Heinke, C O; Hut, P; Ivanova, N; Maccarone, T J; Ransom, S M; Webb, N A

    2006-01-01

    This article was co-authored by all invited speakers at the Joint Discussion on `Neutron Stars and Black Holes in Star Clusters,' which took place during the IAU General Assembly in Prague, Czech Republic, on August 17 and 18, 2006. Each section presents a short summary of recent developments in a key area of research, incorporating the main ideas expressed during the corresponding panel discussion at the meeting. Our meeting, which had close to 300 registered participants, was broadly aimed at the large community of astronomers around the world working on the formation and evolution of compact objects and interacting binary systems in dense star clusters, such as globular clusters and galactic nuclei. Great advances have occurred in this field during the past few years, including the introduction of fundamentally new theoretical paradigms for the formation and evolution of compact objects in binaries as well as countless new discoveries by astronomers that have challenged many accepted models. Some of the hi...

  9. Approximate universal relations for neutron stars and quark stars

    Science.gov (United States)

    Yagi, Kent; Yunes, Nicolás

    2017-04-01

    Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia (I), its tidal Love number (Love) and its quadrupole moment (Q), the so-called I-Love-Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astrophysical tests of General Relativity that are independent of the equation of state. We here review how the universal relations come about and all the applications that have been devised to date.

  10. Nucleosynthesis in decompressing neutron star matter

    CERN Document Server

    Jaikumar, P; Otsuki, K; Ouyed, R; Jaikumar, Prashanth; Meyer, Bradley S.; Otsuki, Kaori; Ouyed, Rachid

    2006-01-01

    We explore heavy-element nucleosynthesis by rapid neutron capture (r-process) in the decompressing ejecta from the surface of a neutron star. The decompression is triggered by a violent phase transition to strange quark matter (quark-nova scenario). The presence of neutron-rich large Z nuclei (40,95)<(Z,A)<(70,177), the large neutron-to-seed ratio, and the low electron fraction Ye ~ 0.03 in the decompressing ejecta present favorable conditions for the r-process. We perform network calculations that are adapted to the quark-nova conditions, and which mimic usual (n-\\gamma) equilibrium r-process calculations during the initially cold decompression phase. They match to dynamical r-process calculations at densities below neutron drip (4x10^11 g/cc). We present results for the final element abundance distribution with and without heating from nuclear reactions, and compare to the solar abundance pattern of r-process elements. We highlight the distinguishing features of quark-novae by contrasting it with conv...

  11. 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.

  12. Extreme neutron stars from Extended Theories of Gravity

    CERN Document Server

    Astashenok, Artyom V; Odintsov, Sergei D

    2014-01-01

    We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from $f(R)$ and $f(\\cal G)$ extensions of General Relativity where functions of the Ricci curvature invariant $R$ and the Gauss-Bonnet invariant ${\\cal G}$ are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in $f(R)$ gravity. In principle, massive stars with $M> 4 M_{\\odot}$ can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities $\\rho_{c}\\sim 1.5-2.0$ GeV/fm$^{3}$) are possible considering quadratic corrections of $f(\\cal {G})$ gravity. The magnetic field strength in the star center is of order $6-8\\times 10^{18}$ G. In general, we can say that other branches of ...

  13. Complete equation of state for neutron stars using the relativistic Hartree-Fock approximation

    Energy Technology Data Exchange (ETDEWEB)

    Miyatsu, Tsuyoshi; Cheoun, Myung-Ki [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Yamamuro, Sachiko; Nakazato, Ken' ichiro [Department of Physics, Faculty of Science and Technology, Tokyo University of Science (TUS), Noda 278-8510 (Japan)

    2014-05-02

    We construct the equation of state in a wide-density range for neutron stars within relativistic Hartree-Fock approximation. The properties of uniform and nonuniform nuclear matter are studied consistently. The tensor couplings of vector mesons to baryons due to exchange contributions (Fock terms) are included, and the change of baryon internal structure in matter is also taken into account using the quark-meson coupling model. The Thomas-Fermi calculation is adopted to describe nonuniform matter, where the lattice of nuclei and the neutron drip out of nuclei are considered. Even if hyperons exist in the core of a neutron star, we obtain the maximum neutron-star mass of 1.95M{sub ⊙}, which is consistent with the recently observed massive pulsar, PSR J1614-2230. In addition, the strange vector (φ) meson also plays a important role in supporting a massive neutron star.

  14. Gravitational waves from spinning black hole-neutron star binaries: dependence on black hole spins and on neutron star equations of state

    Science.gov (United States)

    Kyutoku, Koutarou; Okawa, Hirotada; Shibata, Masaru; Taniguchi, Keisuke

    2011-09-01

    We study the merger of black hole-neutron star binaries with a variety of black hole spins aligned or antialigned with the orbital angular momentum, and with the mass ratio in the range MBH/MNS=2-5, where MBH and MNS are the mass of the black hole and neutron star, respectively. We model neutron-star matter by systematically parametrized piecewise polytropic equations of state. The initial condition is computed in the puncture framework adopting an isolated horizon framework to estimate the black hole spin and assuming an irrotational velocity field for the fluid inside the neutron star. Dynamical simulations are performed in full general relativity by an adaptive-mesh refinement code, SACRA. The treatment of hydrodynamic equations and estimation of the disk mass are improved. We find that the neutron star is tidally disrupted irrespective of the mass ratio when the black hole has a moderately large prograde spin, whereas only binaries with low mass ratios, MBH/MNS≲3, or small compactnesses of the neutron stars bring the tidal disruption when the black hole spin is zero or retrograde. The mass of the remnant disk is accordingly large as ≳0.1M⊙, which is required by central engines of short gamma-ray bursts, if the black hole spin is prograde. Information of the tidal disruption is reflected in a clear relation between the compactness of the neutron star and an appropriately defined “cutoff frequency” in the gravitational-wave spectrum, above which the spectrum damps exponentially. We find that the tidal disruption of the neutron star and excitation of the quasinormal mode of the remnant black hole occur in a compatible manner in high mass-ratio binaries with the prograde black hole spin. The correlation between the compactness and the cutoff frequency still holds for such cases. It is also suggested by extrapolation that the merger of an extremely spinning black hole and an irrotational neutron star binary does not lead to the formation of an overspinning

  15. Deconfinement Phase Transition Heating and Thermal Evolution of Neutron Stars

    CERN Document Server

    Kang, Miao; Wang, Xiaodong

    2007-01-01

    The deconfinement phase transition will lead to the release of latent heat during spins down of neutron stars if the transition is the first-order one.We have investigated the thermal evolution of neutron stars undergoing such deconfinement phase transition. The results show that neutron stars may be heated to higher temperature.This feature could be particularly interesting for high temperature of low-magnetic field millisecond pulsar at late stage.

  16. Isolated neutron stars in the galaxy: from magnetars to antimagnetars

    Energy Technology Data Exchange (ETDEWEB)

    Boldin, P. A., E-mail: boldin.pavel@gmail.com [Moscow Engineering Physics Institute (State University) (Russian Federation); Popov, S. B., E-mail: polar@sai.msu.ru [Moscow State University, Sternberg Astronomical Institute (Russian Federation)

    2012-07-15

    Using the model with decaying magnetic fields it is possible to describe with one smooth (log-Gaussian) initial magnetic field distribution three types of isolated neutron stars: radiopulsar, magnetars, and cooling close-by compact objects. The same model is used here to make predictions for old accreting isolated neutron stars. It is shown that using the updated field distribution we predict a significant fraction of isolated neutron stars at the stage of accretion despite long subsonic propeller stage.

  17. The Effects of δ Meson on the Neutron Star Cooling

    Institute of Scientific and Technical Information of China (English)

    许妍; 刘广洲; 吴姚睿; 朱明枫; 喻孜; 王红岩; 赵恩广

    2012-01-01

    In the framework of the relativistic mean field theory, the isovector scalar interaction is considered by exchanging δ meson to study the influence of δ meson on the cooling properties of neutron star matter. The calculation results show that with the inclusion of δ meson, the neutrino emissivity of the direct Urca processes increases, and thus enhances the cooling of neutron star matter. When strong proton superfluidity is considered, the theoretical cooling curves agree with the observed thermal radiation for isolated neutron stars.

  18. Neutrino emissivity of the nucleon direct URCA process for rotational traditional and hyperonic neutron stars

    Science.gov (United States)

    Zhang, Nai-Bo; Wang, Shou-Yu; Qi, Bin; Gao, Jian-Hua; Sun, Bao-Yuan

    2017-07-01

    Based on covariant density functional theory, we study the effects of rotation on the nucleon direct URCA (N-DURCA) process for traditional and hyperonic neutron stars. The calculated results indicate that, for a fixed mass sequence of rotational traditional neutron stars, the neutrino emissivity of the star is nearly invariant with increasing frequency, while it always increases for rotational hyperonic neutron stars. Thus, rotation has different effects on the N-DURCA process for these two kinds of neutron stars. Supported by National Natural Science Foundation of China (11545011, 11405096), the Shandong Natural Science Foundation (ZR2014AQ012), the Young Scholars Program of Shandong University, Weihai (2015WHWLJH01) and the Fundamental Research Funds for the Central Universities (lzujbky-2016-30)

  19. Measuring Ejecta from Inspiralling Binary Neutron Stars using Smoothed-particle Hydrodynamics

    Science.gov (United States)

    Rizzo, Monica; O'Shaughnessy, Richard; Faber, Joshua

    2017-01-01

    Gravitational waves, detectable perturbations in spacetime, can arise from astrophysical systems such as inspiralling binary neutron stars, the remnants of the core collapse of massive stars. In the inspiral process, neutron stars, composed of highly dense nuclear matter, are torn apart by each others gravity and eject matter. Using both gravitational waves and direct observations of ejected matter, we may gain valuable new information about the composition of neutron stars. Using several previously studied test cases, we seek to determine how the amount of ejected matter depends on the physical parameters of these systems. To do this, we use a particle-based hydrodynamics code which can accurately simulate binary neutron star systems with variable equation of state, spin, mass ratio, and eccentricity, and includes the lowest-order effects from gravitational wave emission. I would like to thank RIT's College of Science as well as the Center for Computational Relativity and Gravitation for support and funding.

  20. Prospects For High Frequency Burst Searches Following Binary Neutron Star Coalescence With Advanced Gravitational Wave Detectors

    CERN Document Server

    Clark, J; Cadonati, L; Janka, H -T; Pankow, C; Stergioulas, N

    2014-01-01

    The equation of state plays a critical role in the physics of the merger of two neutron stars. Recent numerical simulations with microphysical equation of state suggest the outcome of such events depends on the mass of the neutron stars. For less massive systems, simulations favor the formation of a hypermassive, quasi-stable neutron star, whose oscillations produce a short, high frequency burst of gravitational radiation. Its dominant frequency content is tightly correlated with the radius of the neutron star, and its measurement can be used to constrain the supranuclear equation of state. In contrast, the merger of higher mass systems results in prompt gravitational collapse to a black hole. We have developed an algorithm which combines waveform reconstruction from a morphology-independent search for gravitational wave transients with Bayesian model selection, to discriminate between post-merger scenarios and accurately measure the dominant oscillation frequency. We demonstrate the efficacy of the method us...

  1. 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.

  2. Evolutionary Channels for the Formation of Double Neutron Stars

    CERN Document Server

    Andrews, Jeff J; Kalogera, Vicky; Willems, Bart

    2014-01-01

    We analyze binary population models of double-neutron stars and compare results to the accurately measured orbital periods and eccentricities of the eight known such systems in our Galaxy. In contrast to past similar studies, we especially focus on the dominant evolutionary channels (we identify three); for the first time, we use a detailed understanding of the evolutionary history of three double neutron stars as actual constraints on the population models. We find that the evolutionary constraints derived from the double pulsar are particularly tight, and less than half of the examined models survive the full set of constraints. The top-likelihood surviving models yield constraints on the key binary evolution parameters, but most interestingly reveal (i) the need for electron-capture supernovae from relatively low-mass degenerate, progenitor cores, and (ii) the most likely evolutionary paths for the rest of the known double neutron stars. In particular, we find that J1913+16 likely went through a phase of C...

  3. The Dynamical Evolution of Black Hole-Neutron Star Binaries in General Relativity: Simulations of Tidal Disruption

    CERN Document Server

    Faber, J A; Shapiro, S L; Taniguchi, K; Rasio, F A; Faber, Joshua A.; Baumgarte, Thomas W.; Shapiro, Stuart L.; Taniguchi, Keisuke; Rasio, Frederic A.

    2006-01-01

    We calculate the first dynamical evolutions of merging black hole-neutron star binaries that construct the combined black hole-neutron star spacetime in a general relativistic framework. We treat the metric in the conformal flatness approximation, and assume that the black hole mass is sufficiently large compared to that of the neutron star so that the black hole remains fixed in space. Using a spheroidal spectral methods solver, we solve the resulting field equations for a neutron star orbiting a Schwarzschild black hole. The matter is evolved using a relativistic, Lagrangian, smoothed particle hydrodynamics (SPH) treatment. We take as our initial data recent quasiequilibrium models for synchronized neutron star polytropes generated as solutions of the conformal thin-sandwich (CTS) decomposition of the Einstein field equations. We are able to construct from these models relaxed SPH configurations whose profiles show good agreement with CTS solutions. Our adiabatic evolution calculations for neutron stars wit...

  4. Tidal deformability of neutron and hyperon star with relativistic mean field equations of state

    CERN Document Server

    Kumar, Bharat; Patra, S K

    2016-01-01

    We systematically study the tidal deformability for neutron and hyperon stars using relativistic mean field (RMF) equations of state (EOSs). The tidal effect plays an important role during the early part of the evolution of compact binaries. Although, the deformability associated with the EOSs has a small correction, it gives a clean gravitational wave signature in binary inspiral. These are characterized by various love numbers kl (l=2, 3, 4), that depend on the EOS of a star for a given mass and radius. The tidal effect of star could be efficiently measured through advanced LIGO detector from the final stages of inspiraling binary neutron star (BNS) merger.

  5. Tidal deformability of neutron and hyperon stars within relativistic mean field equations of state

    Science.gov (United States)

    Kumar, Bharat; Biswal, S. K.; Patra, S. K.

    2017-01-01

    We systematically study the tidal deformability for neutron and hyperon stars using relativistic mean field equations of state (EOSs). The tidal effect plays an important role during the early part of the evolution of compact binaries. Although, the deformability associated with the EOSs has a small correction, it gives a clean gravitational wave signature in binary inspiral. These are characterized by various Love numbers kl(l =2 ,3 ,4 ), that depend on the EOS of a star for a given mass and radius. The tidal effect of star could be efficiently measured through an advanced LIGO detector from the final stages of an inspiraling binary neutron star merger.

  6. Comparison of Properties of the Simplest Neutron Stars in Three RMF Models

    Institute of Scientific and Technical Information of China (English)

    WANG Guo-Hua; FU Wei-Jie; LIU Yu-Xin

    2008-01-01

    @@ We study some properties of the simplest neutron stars (NSs) in the Glendenning-Moszkowski (GM) model, the hybrid derivative coupling (HD) model and the Zimanyi-Moszkowski (ZM) model in the framework of relativistic mean field (RMF) theory with and without the interaction by exchanging the δ-meson. We show that the maximal mass of the NSs becomes smaller, but the redshift becomes larger from the GM model to the HD model, then to the ZM model. The interaction with the δ-meson exchange enlarges the maximal mass of neutron stars, increases the relative population of charged particles (proton, electron and muon) and descends the relative population of neutron.

  7. Investigating Variability of Quiescent Neutron Stars in the Globular Clusters NGC 6440 and Terzan 5

    CERN Document Server

    Walsh, A R; Bernardini, F

    2014-01-01

    The quiescent spectrum of neutron star low-mass X-ray binaries typically consists of two components - a thermal component associated with emission from the neutron star surface, and a non-thermal power-law component whose origin is not well understood. Spectral fitting of neutron star atmosphere models to the thermal component is one of the leading methods for measuring the neutron star radius. However, it has been known for years that the X-ray spectra of quiescent neutron stars vary between observations. While most quiescent variability is explained through a variable power-law component, the brightest and best-studied object, Cen X-4, requires a change in the thermal component and such thermal variability could be a problem for measuring neutron star radii. In this paper, we significantly increase the number of sources whose quiescent spectra have been studied for variability. We examine 9 potential quiescent neutron stars with luminosities <1E34 erg/s over the course of multiple Chandra observations of...

  8. Nuclear fusion and carbon flashes on neutron stars

    Science.gov (United States)

    Taam, R. E.; Picklum, R. E.

    1978-01-01

    This paper reports on detailed calculations of the thermal evolution of the carbon-burning shells in the envelopes of accreting neutron stars for mass-accretion rates of 1 hundred-billionth to 2 billionths of a solar mass per yr and neutron-star masses of 0.56 and 1.41 solar masses. The work of Hansen and Van Horn (1975) is extended to higher densities, and a more detailed treatment of nuclear processing in the hydrogen- and helium-burning regions is included. Results of steady-state calculations are presented, and results of time-dependent computations are examined for accretion rates of 3 ten-billionths and 1 billionth of solar mass per yr. It is found that two evolutionary sequences lead to carbon flashes and that the carbon abundance at the base of the helium shell is a strong function of accretion rate. Upper limits are placed on the accretion rates at which carbon flashes will be important.

  9. Four-Hair Relations for Differentially Rotating Neutron Stars in the Weak-Field Limit

    CERN Document Server

    Bretz, Joseph; Yunes, Nicolas

    2015-01-01

    The opportunity to study physics at supra-nuclear densities through X-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations determines all of the multipole moments of a neutron star just from the first three (the mass monopole, the current dipole and the mass quadrupole moment) approximately independently of the equation of state. These three-hair relations were found to hold in neutron stars that rotate rigidly, as is the case in old pulsars, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We here extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about r...

  10. Mesoscopic pinning forces in neutron star crusts

    CERN Document Server

    Seveso, Stefano; Grill, Fabrizio; Haskell, Brynmor

    2014-01-01

    The crust of a neutron star is thought to be comprised of a lattice of nuclei immersed in a sea of free electrons and neutrons. As the neutrons are superfluid their angular momentum is carried by an array of quantized vortices. These vortices can pin to the nuclear lattice and prevent the neutron superfluid from spinning down, allowing it to store angular momentum which can then be released catastrophically, giving rise to a pulsar glitch. A crucial ingredient for this model is the maximum pinning force that the lattice can exert on the vortices, as this allows us to estimate the angular momentum that can be exchanged during a glitch. In this paper we perform, for the first time, a detailed and quantitative calculation of the pinning force \\emph{per unit length} acting on a vortex immersed in the crust and resulting from the mesoscopic vortex-lattice interaction. We consider realistic vortex tensions, allow for displacement of the nuclei and average over all possible orientation of the crystal with respect to...

  11. Observational implications of a strong phase transition in the dense matter equation of state for the rotational evolution of neutron stars

    CERN Document Server

    Bejger, M; Haensel, P; Zdunik, J L; Fortin, M

    2016-01-01

    We explore the implications of a strong first-order phase transition region in the dense matter equation of state in the interiors of rotating neutron stars, and the resulting creation of two disjoint families of neutron-stars' configurations (the so-called high-mass twins). Rotating, axisymmetric and stationary stellar configurations are obtained numerically in the framework of general relativity, and their global parameters and stability are studied. The equation of state-induced instability divides stable neutron star configurations into two disjoint families: neutron stars (second family) and hybrid stars (third family), with an overlapping region in mass, the high-mass twin star region. These two regions are divided by an instability strip. Its existence has interesting astrophysical consequences for rotating neutron stars. We note that it provides a "natural" explanation for the rotational frequency cutoff in the observed distribution of neutron stars spins, and for the apparent lack of back-bending in ...

  12. Gravitational Waves from Fallback Accretion onto Neutron Stars

    CERN Document Server

    Piro, Anthony L

    2012-01-01

    Massive stars generally end their lives as neutron stars (NSs) or black holes (BHs), with NS formation typically occurring at the low mass end and collapse to a BH more likely at the high mass end. In an intermediate regime, with a mass range that depends on the uncertain details of rotation and mass loss during the star's life, a NS is initially formed which then experiences fallback accretion and collapse to a BH. The electromagnetic consequence of such an event is not clear. Depending on the progenitor's structure, possibilities range from a long gamma-ray burst to a Type II supernova (that may or may not be jet-powered) to a collapse with a weak electromagnetic signature. Gravitational waves (GWs) provide the exciting opportunity to peer through the envelope of a dying massive star and directly probe what is occurring inside. We explore whether fallback onto young NSs can be detected by ground-based interferometers. When the incoming material has sufficient angular momentum to form a disk, the accretion s...

  13. Magnetic Neutron Stars in f(R) gravity

    CERN Document Server

    Astashenok, Artyom V; Odintsov, Sergei D

    2015-01-01

    Neutron stars with strong magnetic fields are considered in the framework of f(R) gravity. In order to describe dense matter in magnetic field, the model with baryon octet interacting through $\\sigma$$\\rho$$\\omega$-fields is used. The hyperonization process results in softening the equation of state (EoS) and in decreasing the maximal mass. We investigate the effect of strong magnetic field in models involving quadratic and cubic corrections in the Ricci scalar $R$ to the Hilbert-Einstein action. For large fields, the Mass-Radius relation differs considerably from that of General Relativity only for stars with masses close to the maximal one. Another interesting feature is the possible existence of more compact stable stars with extremely large magnetic fields ($\\sim 6\\times 10^{18}$ G instead of $\\sim 4\\times 10^{18}$ G as in General Relativity) in the central regions of the stars. Due to cubic terms, a significant increasing of the maximal mass is possible.

  14. Relativistic superfluid models for rotating neutron stars

    CERN Document Server

    Carter, B

    2001-01-01

    This article starts by providing an introductory overview of the theoretical mechanics of rotating neutron stars as developped to account for the frequency variations, and particularly the discontinuous glitches, observed in pulsars. The theory suggests, and the observations seem to confirm, that an essential role is played by the interaction between the solid crust and inner layers whose superfluid nature allows them to rotate independently. However many significant details remain to be clarified, even in much studied cases such as the Crab and Vela. The second part of this article is more technical, concentrating on just one of the many physical aspects that needs further development, namely the provision of a satisfactorily relativistic (local but not microscopic) treatment of the effects of the neutron superfluidity that is involved.

  15. Rotating proto-neutron stars under strong magnetic fields

    CERN Document Server

    Franzon, B; Schramm, S

    2016-01-01

    In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars (PNSs). A hadronic chiral SU(3) model is applied to cold neutron stars (NS) and proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.

  16. New mass measurements of neutron rich nuclides at the NSCL.

    Science.gov (United States)

    Estrade, Alfredo; Matos, Milan; Amthor, Matthew; Bazin, Daniel; Becerril, Ana; Elliot, Thom; Gade, Alexandra; Galaviz, Daniel; Lorusso, Giuseppe; Pereira, Jorge; Portillo, Mauricio; Rogers, Andrew; Schatz, Hendrik; Shapira, Dan; Smith, Ed; Stolz, Andreas; Wallace, Mark

    2007-10-01

    A mass measurement of exotic isotopes in the region of 68Fe has been performed at the NSCL using the time-of-flight technique recently established. Experimental knowledge of the mass of very neutron rich nuclides is an important input for astrophysical applications, such as nucleosynthesis during the r-process and the evolution of matter in the crust of an accreting neutron star, where present calculations are mostly limited to using theoretical mass extrapolations. We present the details of the experimental set up, as well as preliminary results.

  17. Quark matter droplets in neutron stars

    Science.gov (United States)

    Heiselberg, H.; Pethick, C. J.; Staubo, E. F.

    1993-01-01

    We show that, for physically reasonable bulk and surface properties, the lowest energy state of dense matter consists of quark matter coexisting with nuclear matter in the presence of an essentially uniform background of electrons. We estimate the size and nature of spatial structure in this phase, and show that at the lowest densities the quark matter forms droplets embedded in nuclear matter, whereas at higher densities it can exhibit a variety of different topologies. A finite fraction of the interior of neutron stars could consist of matter in this new phase, which would provide new mechanisms for glitches and cooling.

  18. Quark matter droplets in neutron stars

    Science.gov (United States)

    Heiselberg, H.; Pethick, C. J.; Staubo, E. F.

    1993-01-01

    We show that, for physically reasonable bulk and surface properties, the lowest energy state of dense matter consists of quark matter coexisting with nuclear matter in the presence of an essentially uniform background of electrons. We estimate the size and nature of spatial structure in this phase, and show that at the lowest densities the quark matter forms droplets embedded in nuclear matter, whereas at higher densities it can exhibit a variety of different topologies. A finite fraction of the interior of neutron stars could consist of matter in this new phase, which would provide new mechanisms for glitches and cooling.

  19. Coalescence of Magnetized Binary Neutron Star Systems

    Science.gov (United States)

    Motl, Patrick M.; Anderson, Matthew; Lehner, Luis; Liebling, Steven L.; Neilsen, David; Palenzuela, Carlos; Ponce, Marcelo

    2015-01-01

    We present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. Our simulation tools have recently been improved to incorporate the effects of neutrino cooling and have been generalized to allow for tabular equations of state to describe the degenerate matter. Of particular interest are possible electromagnetic counterparts to the gravitational radiation that emerges from these systems. We focus on magnetospheric interactions that ultimately tap into the gravitational potential energy of the binary to power a Poynting flux and deposition of energy through Joule heating and magnetic reconnection. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  20. Neutron star in the presence of strong magnetic field

    Indian Academy of Sciences (India)

    K K Mohanta; R Mallick; N R Panda; L P Singh; P K Sahu

    2014-05-01

    Compact stars such as neutron stars (NS) can have either hadronic or exotic states like strange quark or colour superconducting matter. Stars can also have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and the quark phases. Observational results suggest huge surface magnetic field in certain NS. Therefore, we study here the effect of strong magnetic field on the respective equation of states (EOS) of matter under extreme conditions. We further study the hadron–quark phase transition in the interiors of NS giving rise to HS in the presence of strong magnetic field. The hadronic matter EOS is described based on RMF theory and we include the effects of strong magnetic fields leading to Landau quantization of the charged particles. For quark phase, we use the simple Massachusetts Institute of Technology (MIT) bag model, assuming density-dependent bag pressure and magnetic field. The magnetic field strength increases from the surface to the centre of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. We finally study, the mass–radius relationship for such types of mixed HS, calculating their maximum mass, and compare them with the recent observations of pulsar PSR J1614-2230, which is about 2 solar mass.

  1. Hans A. Bethe Prize: Neutron Stars and Core-Collapse Supernovae

    Science.gov (United States)

    Lattimer, James

    2015-04-01

    Core-collapse supernovae lead to the formation of neutron stars, and both are sensitive to the dense matter equation of state. Hans Bethe first recognized that the matter in the collapsing core of a massive star has a relatively low entropy which prevents nuclear dissociation until nuclei merge near the nuclear saturation density. This recognition means that collapse continues until the core exceeds the saturation density. This prediction forms the foundation for modern simulations of supernovae. These supernovae sample matter up to about twice nuclear saturation density, but neutron stars are sensitive to the equation of state both near the saturation density and at several times higher densities. Two important recent developments are the discovery of two-solar mass neutron stars and refined experimental determinations of the behavior of the symmetry energy of nuclear matter near the saturation density. Combined with the assumption of causality, they imply that the radii of observed neutron stars are largely independent of their mass, and that this radius is in the range of 11 to 13 km. These theoretical results are not only consistent with expectations from theoretical studies of pure neutron matter, but also accumulated observations of both bursting and cooling neutron stars. In the near future, new pulsar timing data, which could lead to larger measured masses as well as measurements of moments of inertia, X-ray observations, such as from NICER, of bursting and other sources, and gravitational wave observations of neutron stars in merging compact binaries, will provide important new constraints on neutron stars and the dense matter equation of state. DOE DE-FG02-87ER-40317.

  2. The EOS of neutron matter, and the effect of Lambda hyperons to neutron star structure

    Energy Technology Data Exchange (ETDEWEB)

    Gandolfi, Stefano [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-01-13

    The following topics are addressed: the model and the method; equation of state of neutron matter, role of three-neutron force; symmetry energy; Λ-hypernuclei; Λ-neutron matter; and neutron star structure. In summary, quantum Monte Carlo methods are useful to study nuclear systems in a coherent framework; the three-neutron force is the bridge between Esym and neutron star structure; and neutron star observations are becoming competitive with experiments. Λ-nucleon data are very limited, but ΛNN is very important. The role of Λ in neutron stars is far from understood; more ΛN data are needed. The author's conclusion: We cannot conclude anything with present models.

  3. Supernova explosions and the birth of neutron stars

    CERN Document Server

    Janka, H -Th; Müller, B; Scheck, L

    2007-01-01

    We report here on recent progress in understanding the birth conditions of neutron stars and the way how supernovae explode. More sophisticated numerical models have led to the discovery of new phenomena in the supernova core, for example a generic hydrodynamic instability of the stagnant supernova shock against low-mode nonradial deformation and the excitation of gravity-wave activity in the surface and core of the nascent neutron star. Both can have supportive or decisive influence on the inauguration of the explosion, the former by improving the conditions for energy deposition by neutrino heating in the postshock gas, the latter by supplying the developing blast with a flux of acoustic power that adds to the energy transfer by neutrinos. While recent two-dimensional models suggest that the neutrino-driven mechanism may be viable for stars from about 8 solar masses to at least 15 solar masses, acoustic energy input has been advocated as an alternative if neutrino heating fails. Magnetohydrodynamic effects ...

  4. Relativistic Processes and the Internal Structure of Neutron Stars

    CERN Document Server

    Alvarez-Castillo, D E

    2011-01-01

    Models for the internal composition of Dense Compact Stars are reviewed as well as macroscopic properties derived by observations of relativistic processes. Modeling of pure neutron matter Neutron Stars is presented and crust properties are studied by means of a two fluid model.

  5. Isolated neutron stars and studies of their interiors

    OpenAIRE

    Popov, S. B.

    2011-01-01

    In these lectures presented at Baikal summer school on physics of elementary particles and astrophysics 2011, I present a wide view of neutron star astrophysics with special attention paid to young isolated compact objects and studies of the properties of neutron star interiors using astronomical methods.

  6. Magnetic Fields in neutron stars : A theoretical perspective

    NARCIS (Netherlands)

    Reisenegger, A.; Prieto, J.; Benguria, R.; Lai, D.; Araya, P.

    2005-01-01

    Abstract: We present our view of the main physical ingredients determining the evolution of neutron star magnetic fields. This includes the basic properties of neutron star matter, possible scenarios for the origin of the magnetic field, constraints and mechanisms for its evolution, and a discussion

  7. The Thermodynamic Functions in Curved Space of Neutron Star

    Science.gov (United States)

    Hussein, N. A.; Eisa, D. A.; Sayed, E. G.

    2016-04-01

    The aim of this article is to calculate the thermodynamic functions of a neutron star in curved space. We obtained equation of state (EOS) and the excess free energy for a neutron star in curved space up to order n4, where n is the density of particles.

  8. Neutron star models in frames of f (R) gravity

    Energy Technology Data Exchange (ETDEWEB)

    Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, 236041, 14, Nevsky st., Kaliningrad (Russian Federation)

    2009-01-01

    Neutron star models in perturbative f (R) gravity are considered with realistic equations of state. In particular, we consider the FPS and SLy equations of state. The mass-radius relations for f(R)=R+βR(e{sup -R/R₀}₋1) model and for R² models with cubic corrections are obtained. In the case of R2 gravity with cubic corrections, we obtain that at high central densities (ρ > 10 ρ{sub ns} = 2.7 × 10¹⁴ g/cm³ is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ~ 1.9M{sub ⊙}(SLy equation) or to 8.5 km with mass ~ 1.7M{sub ⊙} (FPS equation). This effect can give rise to more compact stars than in GR. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level.

  9. Super-Eddington accretion on to a magnetized neutron star

    Science.gov (United States)

    Chashkina, Anna; Abolmasov, Pavel; Poutanen, Juri

    2017-09-01

    Most of ultraluminous X-ray sources are thought to be objects accreting above their Eddington limits. In the recently identified class of ultraluminous X-ray pulsars, accretor is a neutron star and thus has a fairly small mass with a small Eddington limit. The accretion disc structure around such an object affects important observables such as equilibrium period, period derivative and the size of the magnetosphere. We propose a model of a nearly standard accretion disc interacting with the magnetosphere only in a thin layer near the inner disc rim. Our calculations show that the size of the magnetosphere may be represented as the classical Alfvén radius times a dimensionless factor ξ which depends only on the disc thickness. In the case of radiation-pressure-dominated disc, the size of the magnetosphere does not depend on the mass accretion rate. In general, increasing the disc thickness leads to a larger magnetosphere size in units of the Alfvén radius. For large enough mass accretion rates and magnetic moments, it is important to take into account not only the pressure of the magnetic field and the radiation pressure inside the disc, but also the pressure of the radiation produced close to the surface of the neutron star in accretion column. The magnetospheric size may increase by up to factor of 2 as a result of the effects related to the disc thickness and the irradiation from the central source. Accounting for these effects reduces the estimate of the neutron star magnetic moment by a factor of several orders.

  10. Observing Gravitational Waves From The Post-Merger Phase Of Binary Neutron Star Coalescence

    CERN Document Server

    Clark, James Alexander; Stergioulas, Nikolaos; Shoemaker, Deirdre

    2015-01-01

    We present an effective, low-dimensionality frequency-domain template for the gravitational wave signal from the stellar remnants from binary neutron star coalescence. A principal component decomposition of a suite of numerical simulations of binary neutron star mergers is used to construct orthogonal basis functions for the amplitude and phase spectra of the waveforms for a variety of neutron star equations of state and binary mass configurations. We review the phenomenology of late merger / post-merger gravitational wave emission in binary neutron star coalescence and demonstrate how an understanding of the dynamics during and after the merger leads to the construction of a universal spectrum. We also provide a discussion of the prospects for detecting the post-merger signal in future gravitational wave detectors as a potential contribution to the science case for third generation instruments. The template derived in our analysis achieves $>90\\%$ match across a wide variety of merger waveforms and strain se...

  11. Rapidly Evolving and Luminous Transients Driven by Newly Born Neutron Stars

    CERN Document Server

    Yu, Yun-Wei; Dai, Zi-Gao

    2015-01-01

    We provide a general analysis on the properties of emitting material of some rapidly evolving and luminous transients discovered recently with the Pan-STARRS1 Medium Deep Survey. It is found that these transients are probably produced by a low-mass non-relativistic outflow that is continuously powered by a newly born, rapidly spinning, and highly magnetized neutron star. Such a system could originate from an accretion-induced collapse of a white dwarf or a merger of a neutron star-neutron star binary. Therefore, observations to these transients would be helpful for constraining white dwarf and neutron star physics and/or for searching and identifying gravitational wave signals from the mergers.

  12. Models of magnetized neutron star atmospheres

    CERN Document Server

    Suleimanov, V; Werner, K

    2009-01-01

    We present a new computer code for modeling magnetized neutron star atmospheres in a wide range of magnetic fields (10^{12} - 10^{15} G) and effective temperatures (3 \\times 10^5 - 10^7 K). The atmosphere is assumed to consist either of fully ionized electron-ion plasmas or of partially ionized hydrogen. Vacuum resonance and partial mode conversion are taken into account. Any inclination of the magnetic field relative to the stellar surface is allowed. We use modern opacities of fully or partially ionized plasmas in strong magnetic fields and solve the coupled radiative transfer equations for the normal electromagnetic modes in the plasma. Using this code, we study the possibilities to explain the soft X-ray spectra of isolated neutron stars by different atmosphere models. In particular, the outgoing spectrum using the "sandwich" model (thin atmosphere with a hydrogen layer above a helium layer) is constructed. Thin partially ionized hydrogen atmospheres with vacuum polarization are shown to be able to improv...

  13. Magnetic field evolution of accreting neutron stars

    CERN Document Server

    Istomin, Ya N

    2016-01-01

    The flow of a matter, accreting onto a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the super conducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of $r$ width, narrowing with the depth, i.e. with increasing of the crust density $\\rho$, $r\\propto \\rho^{-1/4}$. Accordingly, the magnetic field $B$ in the tube increases with the depth, $B\\propto...

  14. Relativistic density functional theory for finite nuclei and neutron stars

    CERN Document Server

    Piekarewicz, J

    2015-01-01

    The main goal of the present contribution is a pedagogical introduction to the fascinating world of neutron stars by relying on relativistic density functional theory. Density functional theory provides a powerful--and perhaps unique--framework for the calculation of both the properties of finite nuclei and neutron stars. Given the enormous densities that may be reached in the core of neutron stars, it is essential that such theoretical framework incorporates from the outset the basic principles of Lorentz covariance and special relativity. After a brief historical perspective, we present the necessary details required to compute the equation of state of dense, neutron-rich matter. As the equation of state is all that is needed to compute the structure of neutron stars, we discuss how nuclear physics--particularly certain kind of laboratory experiments--can provide significant constrains on the behavior of neutron-rich matter.

  15. NSMAXG: A new magnetic neutron star spectral model in XSPEC

    CERN Document Server

    Ho, Wynn C G

    2013-01-01

    The excellent sensitivity of X-ray telescopes, such as Chandra and XMM-Newton, is ideal for the study of cooling neutron stars, which can emit at these energies. In order to exploit the wealth of information contained in the high quality data, a thorough knowledge of the radiative properties of neutron star atmospheres is necessary. A key factor affecting photon emission is magnetic fields, and neutron stars are known to have strong surface magnetic fields. Here I briefly describe our latest work on constructing magnetic (B >= 10^10 G) atmosphere models of neutron stars and the NSMAXG implementation of these models in XSPEC. Our results allow for more robust extractions of neutron star parameters from observations.

  16. Kaon Condensates, Nuclear Symmetry Energy and Cooling of Neutron Stars

    CERN Document Server

    Kubis, S

    2003-01-01

    The cooling of neutron stars by URCA processes in the kaon-condensed neutron star matter for various forms of nuclear symmetry energy is investigated. The kaon-nucleon interactions are described by a chiral lagrangian. Nuclear matter energy is parametrized in terms of the isoscalar contribution and the nuclear symmetry energy in the isovector sector. High density behaviour of nuclear symmetry energy plays an essential role in determining the composition of the kaon-condensed neutron star matter which in turn affects the cooling properties. We find that the symmetry energy which decreases at higher densities makes the kaon-condensed neutron star matter fully protonized. This effect inhibits strongly direct URCA processes resulting in slower cooling of neutron stars as only kaon-induced URCA cycles are present. In contrast, for increasing symmetry energy direct URCA processes are allowed in the almost whole density range where the kaon condensation exists.

  17. Limits on Self-Interacting Dark Matter from Neutron Stars

    DEFF Research Database (Denmark)

    Kouvaris, C.

    2012-01-01

    We impose new severe constraints on the self-interactions of fermionic asymmetric dark matter based on observations of nearby old neutron stars. Weakly interacting massive particle (WIMP) self-interactions mediated by Yukawa-type interactions can lower significantly the number of WIMPs necessary...... for gravitational collapse of the WIMP population accumulated in a neutron star. Even nearby neutron stars located at regions of low dark matter density can accrete a sufficient number of WIMPs that can potentially collapse, form a mini black hole, and destroy the host star. Based on this, we derive constraints...

  18. SUPERNOVAE, NEUTRON STARS, AND TWO KINDS OF NEUTRINO

    Energy Technology Data Exchange (ETDEWEB)

    Chiu, H.Y.

    1962-08-15

    The role of neutrinos in the core of a star that has undergone a supernova explosion is discussed. The existence of neutron stars, the Schwarzchild singularity in general relativity, and the meaning of conservation of baryons in the neighborhood of a Schwarzchild singularity are also considered. The problem of detection of neutron stars is discussed. It is concluded that neutron stars are the most plausible alternative for the remnant of the core of a supernova. The neutrino emission processes are divided into two groups: the neutrino associated with the meson (mu) and the production of electron neutrinos. (C.E.S.)

  19. Testing the formation scenarios of binary neutron star systems with measurements of the neutron star moment of inertia

    CERN Document Server

    Newton, William G; Yagi, Kent

    2016-01-01

    Two low mass neutron stars, J0737-3039B and the companion to J1756-2251, show strong evidence of being formed from the collapse of an ONeMg core in an electron capture supernova (ECSN) or in an ultra-stripped iron core collapse supernova (FeCCSN). Using three different systematically generated sets of equations of state we explore the relationship between the moment of inertia of J0737-3039A and the binding energy of the two low mass neutron stars. We find this relationship, a less strict variant of the recently discovered I-Love-Q relations, is nevertheless more robust than a previously explored correlation between the binding energy and the slope of the nuclear symmetry energy L. We find that, if either J0737-3039B or the J1756-2251 companion were formed in an ECSN, no more than 0.06 solar masses could have been lost from the progenitor core, more than four times the mass loss predicted by current supernova modeling. A measurement of the moment of inertia of J0737-3039A to within 10% accuracy from pulsar ti...

  20. Accretion by a Neutron Star Moving at a High Kick Velocity in the Supernova Ejecta

    Institute of Scientific and Technical Information of China (English)

    Xu Zhang; Ye Lu; Yong-Heng Zhao

    2007-01-01

    We suggest a two-dimensional time dependent analytic model to describe the accretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation of a strange star resulting from the accretion is also addressed. The newborn neutron star is assumed to move outward at a kick velocity of vns ~ 103 km s-1, and the accretion flow is treated as a dust flow. When the neutron star travels across the ejecta with high speed, it sweeps up material, and when the accreted mass has reached a critical value, the neutron star will undergo a phase transition,for instance, to become a strange star. Our results show that the accretion rate decreases in a complicated way in time, not just a power law dependence: it drops much faster than the power law derived by Colpi et al. We also found that the total accreted mass and the phase transition of the neutron star depend sensitively on the velocity of supernova ejecta.