Rotational Deformation of Neutron Stars

The rotational deformations of two kinds of neutron stars are calculated by using Hartle‘s slow-rotation formulism. The results show that only the faster rotating neutron star gives an obvious deformation. For the slow rotating neutron star with a period larger than hundreds of millisecond, the rotating deformation is very weak.     

热中子星r-mode 不稳定性的研究

理论上,不稳定的中子星r-mode 能辐射可探测的引力波。采用具有超软对称能的非对称核物质物态方程,并考虑非牛顿引力效应影响,数值计算了由于CFS(Chandrasekhar-Friedmann-Schutz) 不稳定性引起的年轻热中子星的r-mode 不稳定窗口,给出了引力辐射时标和耗散时标随温度的变化关系。利用中子星观测对非牛顿引力参数的约束,给出了热中子星在高温区不稳定窗口边界的约束,并发现较大的非牛顿引力参数对应着较宽的r-mode 不稳定窗口。研究结果可为地面引力辐射探测提供有意义的参考。Theoritically, instable r-mode in neutron star may radiate detectable gravitational waves. In this work,considering the non-Newtonian gravity proposed in the grand unification theories, we numerically calculate the CFS instabilities of r-mode s in the hot neutron stars by using an equation of state with super-soft symmetry energies. The changes of the gravitational radiation time scales and the viscous time scales versus the stellar temperatures are obtained.And according to the constraint of the neutron star observation on the parameter of non-Newtonian gravity, the constraint on the boundary of the instability window is also given. It is found that a stronger non-Newtonian gravity corresponds with a wider r-mode instability window. These results may provide interesting reference for the gravitational wave detection.     

软物态方程支持大质量中子星机制概述

重离子碰撞实验分析及相关理论研究认为高密度非对称核物质可能具有较软的物态方程;在约2～3倍饱和核密度下超子等奇异物质的出现也可能会使物态方程变软。然而,软物态方程却无法支持大质量中子星。脉冲星PSR J1614-2230具有大质量(1.97±0.04)M⊙的观测发现使这一矛盾变得尤为突出。为了解决该矛盾,人们提出了各种可能的物理机制:包括考虑修正的引力理论、修改描述高密度物质物态的理论模型等。在概述和讨论这些能使软物态方程支持大质量中子星的可能物理机制的基础上,还计算和讨论了强电场、强磁场对中子星最大质量的影响,发现强电磁场可以有效地增大中子星的最大质量。     

Equation of State in the σ-ω-ρ Model Supported by the Observational Data of 4U 1608-52 Neutron Star

The properties of the neutron star rotating at 619Hz （which is the spin frequency of 4U 1608-52 neutron star） are investigated by using an equation of state （EOS） of the nuclear matter in the relativistic σ-ω-ρ model. It is shown that the EOS in the relativistic σ-ω-ρ model is supported by the observational mass and radius of the 4U 1608-52 neutron star. Moreover, a
strict constraint on the polar redshift of 4U 1608-52 neutron star is obtained.     

Energy—Momentum Pseudo—tensor of Cylindrical Gravitational Waves of Both the Polarized States

According to the Einstein-Tolman expression of the energy-momentum pseudo-tensor(EMPT),we calculate the EMPT of cylindrical gravitational waves (CGW) of both the polarized states (BPS) in cylindrical polar coordinates and Cartesian coordinates.We find that Cartesian coordinates are the more suitable coordinates to describe the CGW of BPS.     

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.     

Gravitational waves from the axial perturbations of hyperon stars

The eigen-frequencies of the axial w-mode oscillations of hyperon stars are examined.It is shown that as the appearance of hyperons softens the equation of state of the super-density matter,the frequency of gravitational waves from the axial w-mode of hyperon star becomes smaller than that of a traditional neutron star at the same stellar mass.Moreover,the eigenfrequencies of hyperon stars also have scaling universality.It is shown that the EURO thirdgeneration gravitational-wave detector has the potential to detect the gravitational-wave signal emitted from the axial w-mode oscillations of a hyperon star.     

Constraints on Non-Radial Oscillation Modes by Symmetry Energy Slope

The effect of the nuclear symmetry energy slope on the non-radial oscillation f-modes in neutron stars is calculated and discussed. Based on a conservative range of the symmetry energy slope constrained by the experiment and theoretical analysis, a constraint on the frequency and damping time of the gravitational radiation from the f-mode in neutron star is obtained. It is also shown that a higher symmetry energy slope corresponds with a smaller frequency and a longer damping time. Meanwhile, a new set of parameters is given to present the universal properties of the scaled frequency and damping time.     

The mass limit of white dwarfs with strong magnetic fields in general relativity

Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level(2.58M) if a superstrong magnetic field were considered(Das U and Mukhopadhyay B 2013 Phys. Rev.Lett. 110 071102), where the structure of the strongly magnetized white dwarf(SMWD) is calculated in the framework of Newtonian theory(NT). As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect(GRE) in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity(GR) is approximately 16.5% lower than that in NT.More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48 M with BD = 391.5. Then if we further increase the magnetic fields,surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account.