The Properties of Pure Neutron Star

For a given equation of state of neutron matter in the relativistic σ-ω model, ๏๏๏๏๏ including the vacuum fluctuation of neutron and σ meson, the properties of pure neutron star are studied. We find that the maximum mass of pure neutron star is ～ 2.0 M_{\odot}. At the same time, the influence of incompressibility of the nuclear matter to the properties of neutron star is also studied. We also find that the maximum mass of neutron stars decreases as equation of state of neutron matter becomes softer.     

Search for Short-Duration Transient Gravitational Waves Emitted by Neutron Star Glitches

Neutron stars are known to show an accelerated spin-up of their rotational frequency on a short time scale of around 40 s, called a “glitch” in the neutron star. These neutron star glitches can emit short-duration transient gravitational wave signals as f-mode oscillations at frequencies between 1.5 and 3 kHz and damping times of less than a few seconds. The observed rate of neutron star glitches are currently limited by their electromagnetic observations. There could be a population of the isolated neutron stars in the galaxy for which there is no electromagnetic observation, but they can produce gravitational wave signals. Here, the sensitivity of the generic all-sky search for short-duration transients towards neutron star glitches during the Advanced LIGO and Virgo's third observing run using the Coherent WaveBurst algorithm is presented. The prospects of detecting signals from such glitching neutron stars for the upcoming fourth and fifth observing runs of Advanced LIGO and Virgo detectors are also described.     

Casimir Energy in Astrophysics: Gamma-Ray Bursts from QED Vacuum Transitions

Motivated by analogous applications to sonoluminescence, neutron stars mergers are examined in the context of Schwinger's dynamical Casimir effect. When the dielectric properties of the QED vacuum are altered through the introduction of dense matter, energy shifts in the zero-point fluctuations can appear as photon bursts at gamma-ray frequencies. The amount of radiation depends upon the properties and amount of matter in motion and the suddenness of the transition. It is shown that the dynamical Casimir effect can convert sufficient energy of neutron star mergers into gamma rays. Using information extracted from simulations of matter flow in neutron star mergers by Ruffert and Janka, we estimate that the total Casimir energy released can exceed 10 ⁵³ ergs in gamma-ray frequencies. The Casimir energy approach is capable of explaining the most energetic gamma-ray bursts.     

Kaon properties in (proto-)neutron star matter

The modification of kaon and antikaon properties in the interior of (proto-)neutron stars is investigated using a chiral SU(3) model. The parameters of the model are fitted to nuclear-matter saturation properties, baryon octet vacuum masses, hyperon optical potentials and low-energy kaon-nucleon scattering lengths. We study the kaon/antikaon medium modification and explore the possibility of antikaon condensation in (proto-)neutron star matter at zero as well as finite temperature/entropy and neutrino content. The effect of hyperons on kaon and antikaon optical potentials is also investigated at different stages of the neutron star evolution.     

Hypernuclear physics for neutron stars

The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon–nucleon and hyperon–hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Nonmesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.     

Ultimate energy density of observable cold baryonic matter

We demonstrate that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter. An equation of state-independent expression satisfied by both normal neutron stars and self-bound quark matter stars is derived for the largest energy density of matter inside stars as a function of their masses. The largest observed mass sets the lowest upper limit to the density. Implications from existing and future neutron star mass measurements are discussed.     

Constraints on the symmetry energy using the mass-radius relation of neutron stars

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 radius expansion bursts and on thermal emissions from quiescent low-mass X-ray binaries. While none of these observations can, at the present time, determine individual neutron star radii to better than 20% accuracy, the body of observations can be used with Bayesian techniques to effectively constrain them to higher precision. These techniques invert the structure equations and obtain estimates of the pressure-density relation of neutron star matter, not only near n_s, but up to the highest densities found in neutron star interiors. The estimates we derive for neutron star radii are in concordance with predictions from nuclear experiment and theory.     

Accreting neutron stars as probes of dense matter physics

There are over 100 accreting neutron stars in our galaxy, in which matter (typically H/He) is tidally transferred from a secondary companion to the neutron star. Accretion of this matter perturbs the thermal structure of the interior away from that of an isolated cooling neutron star. In this paper. we review how this accretion induces reactions in the crust of the neutron star that keep the interior hot. If the accretion is intermittent, then the heated surface layers are directly observable when accretion stops. This heating also affects the unstable ignition of light elements in the neutron star envelope. Observations of the neutron star cooling following an accretion outburst can in principle constrain the thermal properties of the crust and core.     

Properties of Neutron Stars Rotating at Kepler Frequency with Uniform Strong Magnetic Field

A uniform strong magnetic field is considered in calculating the properties of neutron star rotating at the Kepler frequency. The results show that the effect of the magnetic field on the properties of neutron star is evident, and the properties of the neutron stars rotating at the Kepler frequency can be used as a criterion to the equations of states of the neutron star matters.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

Maximum elastic deformations of compact stars with exotic equations of state

I make the first estimates of maximum elastic quadrupole deformations sustainable by alternatives to conventional neutron stars. Solid strange quark stars might sustain maximum ellipticities (dimensionless quadrupoles) up to a few times rather than a few times for conventional neutron stars, and hybrid quark-baryon or meson-condensate stars might sustain up to . Most of the difference is due to the shear modulus, which can be up to rather than in the inner crust of a conventional neutron star. Maximum solid strange star ellipticities are comparable to upper limits obtained for several known pulsars in a recent gravitational-wave search by LIGO. Maximum ellipticities of the more robust hybrid model will be detectable by LIGO at initial design sensitivity. A large shear modulus also strengthens the case for starquakes as an explanation for frequent pulsar glitches.     

Formation of Annihilation-Cyclotron Lines in Strong Magnetic Fields Near Neutron Stars

We study cyclotron and polarization spectral features in magnetized vacuum at frequencies near the one-photon annihilation resonance in a subcritical magnetic field. On the basis of this study, we propose a new method for determination of the neutron-star magnetic field. Using the dipole-field model, we show that detection of the annihilation line in absorption and an additional line in emission at MeV energies is evidence of the existence of a magnetic field (2.8-3.6)· 10¹²G on the surface of a neutron star.     

磁荷对中子星质量半径比的约束

讨论了荷电(磁)质点的量子力学波方程及其解. 由磁场中解的奇异性讨论了磁单极的存在; 由Rubakov-Callan模型推知中子星可能含有大量磁单极. 然后采用中子星的结构方程, 讨论了磁荷对中子星质量半径比的约束, 分别得到了磁荷对中子星质量半径比上限的影响 和磁荷对中子星质量半径比下限的影响的数学表达式. 关键词： 磁单极 中子星 质量半径比     

Spin polarised nuclear matter and its application to neutron stars

An equation of state (EOS) of nuclear matter with explicit inclusion of a spin-isospin dependent force is constructed from a finite range, momentum and density dependent effective interaction. This EOS is found to be in good agreement with those obtained from more sophisticated models for unpolarised nuclear matter. Introducing spin degrees of freedom, it is found that it is possible for neutron matter to undergo a ferromagnetic transition at densities realisable in the core of neutron stars. The maximum mass and the surface magnetic field of the neutron star can be fairly explained in this model. Since finding quark matter rather than hadronic matter at the core of neutron stars is a possibility, the proposed EOS is also applied to the study of hybrid stars. It is found using the bag model picture that one can in principle describe both the mass as well as the surface magnetic field of hybrid stars satisfactorily.     

Observing quantum vacuum lensing in a neutron star binary system

In this Letter we study the propagation of light in the neighborhood of magnetized neutron stars. Because of the optical properties of quantum vacuum in the presence of a magnetic field, the light emitted by background astronomical objects is deviated, giving rise to a phenomenon of the same kind as the gravitational one. We give a quantitative estimation of this effect, and we discuss the possibility of its observation. We show that this effect could be detected by monitoring the evolution of the recently discovered double neutron star system J0737-3039.     

Quark deconfinement in neutron star cores

Whether or not the deconfined quark phase exists in neutron star cores is an open question. We use two realistic effective quark models, the three-flavor Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to describe the neutron star matter. We show that the modified quark-meson coupling model, which is fixed by reproducing the saturation properties of nuclear matter, can be consistent with the experimental constraints from nuclear collisions. After constructing possible hybrid equations of state (EOSes) with an unpaired or color superconducting quark phase with the assumption of the sharp hadron-quark phase transition, we discuss the observational constraints from neutron stars on the EOSes. It is found that the neutron star with pure quark matter core is unstable and the hadronic phase with hyperons is denied, while hybrid EOSes with a two-flavor color superconducting phase or unpaired quark matter phase are both allowed by the tight and most reliable constraints from two stars Ter 5 I and EXO 0748-676. And the hybrid EOS with an unpaired quark matter phase is allowed even compared with the tightest constraint from the most massive pulsar star PSR J0751+1807.     

Magnetic collapse of a neutron gas: Can magnetars indeed be formed?

A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular to than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking this as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and a meson condensate, a strange star, or a highly distorted black hole or black ”cigar”, but not a magnetar, if viewed as a superstrongly magnetized neutron star. However, we do not exclude the possibility of superstrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars. Received: 25 November 2002 / Revised version: 25 February 2003 / Published online: 5 May 2003     

TeV mu neutrinos from young neutron stars

Neutron stars are efficient accelerators for bringing charges up to relativistic energies. We show that if positive ions are accelerated to approximately 1 PeV near the surface of a young neutron star (t(age) less than or nearly 10(5) yr), protons interacting with the star's radiation field produce beamed mu neutrinos with energies of approximately 50 TeV that could produce the brightest neutrino sources at these energies yet proposed. These neutrinos would be coincident with the radio beam, so that, if the star is detected as a radio pulsar, the neutrino beam will sweep the Earth; the star would be a "neutrino pulsar." Looking for nu(mu) emission from young neutron stars will provide a valuable probe of the energetics of the neutron star magnetosphere.     

High-energy approximations to nuclear scattering: W. E. Frahn and B. Schürmann. Physics Department,University of Cape Town,Rondebosch (Cape), South Africa

The effect of slow rotation on the dipole magnetic field of neutron stars is studied. It is shown that the differential rotation of inertial frames produced by the effect of “dragging of inertial frames” induces an additional component of electric field outside the star. This new component, as well as the usual electromagnetic components, vanishes as in the limit of collapse of a star to its Schwarzschild radius. For typical neutron stars, the electric quadrupole moment is about half that obtainable from a flat space analysis.     

中子星内壳层的物态方程和质子丰度

求解了恒定均匀的强磁场中核子的能谱和波函数，在手征表象中给出含核子反常磁矩(AMM)项的Dirac方程的解；并且计算了中子星内壳层物质的物态方程(EOS)和粒子丰度，发现在强磁场中磁能将使中子星内壳层的压强增加但物质仍然是丰中子，AMM项对质子的极化度有明显效应.