大质量中子星PSR J0348+0432原生星的组成与结构

在相对论平均场理论中考虑重子八重态,选取每重子熵S=1或S=2,集中研究讨论了熵效应对大质量中子星PSR J0348+0432原生星性质的影响.利用GL85核子耦合参数组计算了PSR J0348+0432的质量,将该参数组推广来计算每重子熵S=1或S=2时原生中子星的性质.结果发现原生中子星较零温中子星会有更多超子出现,且原生中子星的温度越往内部温度越高,超子的出现会降低内部温度.熵会增大大质量原生中子星的质量,这种增加效应超过超子出现减小大质量中子星质量的效应.熵会增加原生中子星的半径,即原生中子星的冷却是一个星体收缩的过程.     

中子星内部中微子辐射的相对论修正

通过相对论平均场理论和相关的弱相互作用冷却理论,在有、无超子两种情况下的中子星物质中研究含相对论效应的中子星冷却性质,并且与非相对论情况进行对比分析.考虑到极微小尺度上的引力会偏离牛顿引力,引入引力修正效应.结果表明中微子辐射的相对论效应降低了中微子发射率、发光度以及星体的冷却速度.在考虑引力修正的无超子的中子星物质中,相对论效应所引起的星体冷却速度降幅最大,对于两倍太阳质量的传统物质中子星可达56%,而超子物质中降幅最小,约为38%.     

超子对冷中子星物理性质的影响

本文将Walecka(1974)提出的平均场模型推广到包括重子八重态的所有重子情况。讨论了超子对冷中子星物理性质的影响。没有预先假定相互作用的SU(3)对称性,给出了完整的理论结果。对SU(3)对称相互作用情况进行了计算。当ρ=4.43×10~(14)gcm~(-3)时,超子开始出现,其影响是使物态方程有约8％的软化。所得到的中子星最大质量及相应的星体半径、转动惯量和中心密度分别为:2.37M_⊙,11.1km,4.3×10~(45)gcm~2和2.32×10~(15)gcm~(-3)。     

强作用对奇异星观测效应的影响

奇异星是类似于中子星的曲奇异夸克物质组成的致密天体。本文研究了夸克这间的强作用对奇异星观测效应的影响。我们认为：（１）中子星转变为奇异星的行为是一种大的周期突变（ｇｌｉｔｃｈ）现象，这种现象取决于夸克间的强作用；（２）强作用使高温奇异星的振动阻尼也有效，这可能是驱动超新星爆发的新机制；（３）强作用加强了高温情形下奇异星和中子星在转动上的差别，奇异星的最小周期比中子星的小。     

∑超子在饱和核物质中的势深度与前身中子星转动惯量

利用相对论平均场理论并考虑重子八重态{n,p,Λ,∑-,∑0,∑+,Ξ-,Ξ0},计算研究了∑超子在饱和核物质中的势深度U(N)∑对前身中子星(PNS)转动惯量的影响.研究发现:当U(N)∑依次取吸引势-30 MeV、-20 MeV、-10 MeV和0 MeV时,前身中子星相应于最大质量的转动惯量分别增大0.44%、0.29%和0.08%;当U(N)∑依次取排斥势+10 MeV、+20 MeV和+30 MeV时,前身中子星相应于最大质量的转动惯量分别增大0.06%和0.10%.取吸引势时的U(N)∑对相应于最大质量的转动惯量的影响较之取排斥势时的U(N)∑对它的影响大数倍.     

夸克物质与夸克星

二十世纪六七十年代强子结构研究的进展使人们认识到了亚核子--夸克--的存在,随后,实验和理论上关于夸克之间作用渐近自由性质的发现使学者们明确地提出了"夸克物质"的概念.理论上预言的这种物质是否真的存在将在很大程度上检验目前基本强作用的理论.夸克星就是夸克物质的可能存在形式之一,相关研究也是人们探索超核密度物质状态的重要途径,该文简述脉冲星、中子星及夸克星的研究历史,总结了近年来夸克物质与夸克星研究的重要成果,指出了夸克星与一般中子星的异同以及若干夸克星候选体.     

新状态方程下中子星的性质

利用扩展的Skyrme作用可从Hartree-Fock多体理论中给出一种新的状态方程。本文在这个状态方程的基础上研究了静态中子星的性质。对于SKM和SG2这两个较好的Skyrme相互作用模型计算得到中子星的最大质量分别为Mmax=1.7M。，Max=1.67M。，此外，本文还研究了中子星的其它性质，如引力红移、惯量矩等，计算结果与观测以及Glitch模型符合。最后还发现在这种状态方程下，中子星冷却仅能通过冷却速度相对较慢的修正的Urca过程来实现。为便于比较，文中还计算了AV14＋TBF和Paris TBF这两种三体相互作用模型下的中子星的性质。     

奇异星周围的中微子主导吸积流

为统一解释伽玛射线暴(简称伽玛暴)与暴后再活动,提出了一个新的伽玛暴中心引擎模型一“奇异星-NDAF”模型(NDAF:Neutrino Dominated Accretion Flow,中微子主导吸积流),并计算了奇异星周围NDAF的结构.与其他中心致密天体不同的是,奇异星会向吸积流反馈以中微子为载体的奇异化相变能量.不考虑NDAF与奇异星的摩擦,结果表明:奇异星周围NDAF的结构对吸积率非常敏感;当吸积率大于0.18 Mo.S-1时,“奇异星-NDAF”模型能统一解释伽玛暴与暴后再活动,这个范围大于无摩擦的“中子星-NDAF”模型能统一解释的范围;在统一解释的情形下, “奇异星-NDAF”模型湮灭总能量的分布非常宽阔,当吸积率大于0.3 M0.S--1时,湮灭总能量大于1051 erg;最后,当吸积率大于0.3 M0.S-1时,“奇异星-NDAF”模型的湮灭光度超过同等吸积率下“黑洞-NDAF”模型一个多量级,有利于解释某些光度极大的伽玛暴.     

高密物质的一种状态方程和中子星的结构

我们用改进的平均场方法计算了核密度以上物质的状态方程,并用中子星结构方程计算了中子星结构,得出引力质量M_G=1.7M_⊙,转动惯量I=1.62×10~(45)g-cm~2。结果表明,这些值与观测值符合的较好;高密物质相互作用模型的选取直接影响到中子星结构的特征量,同时可看出,用改进的平均场方法可使非相对论和相对论理论所推算的中子星的质量和转动惯量之间的差距明显地缩小。     

中子星之谜

１９３２年,在发现中子后不久,苏联学者朗道就预言在宇宙中可能存在中子星。两年后,巴德和茨维基甚至明确提出超新星爆发可以产生中子星。当人们第一次听到这种小得惊人、密度大得出奇的恒星,一定会问,真有这样的恒星吗？当初,在物理学家提出宇宙中可能存在中子星时...     

Describing neutron stars by the relativistic mean field theory

Neutron stars are studied in the framework of the relativistic mean field theory of interacting nucleons, hyperons, and mesons. Within the hadronic freedom, the cores of neutron stars are found to be dominated by hyperons when the density is sufficiently high. The influence of hyperon coupling constants on the transition from a neutron star to a hyperon-dominated strange neutron star is also investigated. It is found that the transition density gets its minimum value when the ratio of hyperon coupling constant to nucleon's takes the value of 0.65, and the calculated maximum mass of the neutron star is 1.4 M which lies within the range of the observational results.     

Exotic bulk viscosity and its influence on neutron star r-modes

We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that the instability is effectively suppressed.      

Neutron stars and the equation of state

The interior of neutron stars consists of the densest, although relatively cold, matter known in the universe. Here, baryon number densities might reach values close to ten times the nuclear saturation density. These suggest that the constituents of neutron star cores not only consist of nucleons, but also of more exotic baryons like hyperons or a phase of deconfined quarks. We discuss the consequences of such exotic particles on the gross properties and phenomenology of neutron stars. In addition, we determine the general phase structure of dense and also hot matter in the chiral parity-doublet model and confront model results with the recent constraints derived from the neutron star merger observation.     

Effects of hyperons on the vibrations of neutron stars

We calculate the effects of hyperons and resonance particles on the vibrations of neutron stars. Vibrating neutron stars can store large amounts of energy in their vibrations; the interaction of the vibrations with the atmosphere would produce electromagnetic radiation. If any process damps out the vibrations rapidly on an astronomical time scale ( 1000 years) then vibrating neutron stars are not likely to be found. Previous work indicates that radiation by a neutrino URCA process (N+NP+N+e ^–+ ) does not rapidly damp many of the neutron star models. Some neutron stars are predicted to contain massive baryons; here we study thermal damping by nonequilibrium reactions involving these baryons.During vibrations the thermodynamic equilibrium state is changed and particle reactions attempt to restore equilibrium. If the reaction rates per particle are very rapid or slow compared to the frequency of vibration the system follows almost the same pressure-volume curve through both parts of the gas cycle, and very little work is done. In the intermediate case, when reaction rates are comparable to the frequency, damping is rapid.We find that the reaction rates for weak interactions such asN+NP+^– (the ^– is the first hyperon to appear with increasing density in degenerate neutron star matter) are of the right magnitude to cause rapid damping. If there is a hyperon region in the star then it cannot sustain vibrations. We also consider the much faster (and hence less important) processN+NP+^–.     

A microscopic equation of state for protoneutron stars

We study the structure of protoneutron stars within the finite-temperature Brueckner–Bethe–Goldstone many-body theory. If nucleons, hyperons, and leptons are present in the stellar core, we find that neutrino trapping stiffens considerably the equation of state, because hyperon onsets are shifted to larger baryon density. However, the value of the critical mass turns out to be smaller than the “canonical” value 1.44M _⊙. We find that the inclusion of a hadron-quark phase transition increases the critical mass and stabilizes it at about 1.5–1.6M _⊙.      

Constraints the properties of neutron star matter from the mass of neutron star PSR J1614-2230

The constraints on the properties of neutron star matter from the mass of neutron star PSR J1614-2230 are examined in the framework of the relativistic mean field theory. We find that there are little differences between the σ potentials of large mass neutron star and those of canonnical mass neutron star. For potentials of ω, ρ, neutrons and electrons, the values corresponding to the large mass neutron star are larger than those to the canonnical mass neutron star as the baryon number density is more than a certain value. We also find that for the relative particle number density of electrons, muons, neutrons and protons and the pressure of the neutron star, the values corresponding to the large mass neutron star are far larger than those to the canonnical mass neutron star. For the relative particle number density of hyperons Λ, Σ^?, Σ⁰, Σ⁺ and Ξ^?, the values corresponding to the large mass neutron star are far smaller than those to the canonnical mass neutron star. These mean that the larger mass of neutron star is more advantageous to the production of protons but is not advantageous to the production of hyperons.     

Neutrino synchrotron radiation

The neutrino luminosity of several models of neutron stars has been computed according to the photon-neutrino coupling theory and compared with that of the current-current coupling theory. It is shown that the NSR process alone should have cooled the core of the neutron star created in a supernova explosion in 1954 A.D. to a temperature around 2×10⁹ K according to the photon-neutrino coupling theory.The emission power of the star is greater than the emission power of the X-ray source discovered in the Crab Nebula; so the source may be interpreted as the thermal radiation of the star according to the photon-neutrino coupling theory.     

Effect of hyperons on the physical properties of neutron stars

In this paper we generalize Walecka's (1974) mean field model to include the case of all the baryons in the eightfold state. We discuss the effect of hyperons and the physical properties of cool neutron stars. A general theoretical result is given without presupposing the SU(3) symmetry, and numerical calculation was made on assuming the SU(3) symmetry. When ρ = 4.43(+14) g/cm³, hyperons begin to appear; their effect is to soften the equation of state by about 8%. We obtained the following values: maximum mass of a neutron star, 2.37 M; the corresponding radius, 11.1 km; rotational inertia, 4.3 (+45) g cm²; central density, 2.32 (+15) g/cm³.     

Evolution of neutron star magnetic fields

During the evolution of the neutron star its magnetic field first decays exponentially with the time and then may becomes quasi-stationary. The non-decaying magnetic field of the neutron star is generated by a degenerate electron gas which is in the Landau orbital ferromagnetism (LOFER) state. Possibly, due to the neutron star transition into the LOFER state, magnetic fields remained sufficiently strong in the case of such old magnetic neutron stars as powerful X-ray sources (e.g., Her X-1), millisecond pulsars and the binary pulsar PSR 0655+64.     

Thermal Evolution of Neutron Stars

We present results from simulations of protoneutron star thermal evolution using neutrino opacities that are consistently calculated with the equation of state. When hyperons are allowed to appear in the system, we obtain metastable configurations that after the deleptonization stage become unstable. Concerning the evolution of old neutron stars, we present the results of our investigation on the effect of the Joule heating due to magnetic field dissipation. We conclude that this mechanism can be efficient in maintaining the surface temperature of the star above 3 × 10⁴ - 10⁵ K during a very long time (≥ 100 Myr), comparable with the decay time of the magnetic field. This revised version was published online in July 2006 with corrections to the Cover Date.