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用密度依赖的相对论平均场模型研究中子星物质物态方程

Investigations on the Equation of State of Neutron Star Matter with Density-dependent Relativistic Mean-field Model

  • 摘要: 随着引力波探测以及对中子星质量与半径的高精度测量,中子星作为超新星爆发的剩余产物正吸引着相关领域的高度关注。特别是LIGO和Virgo合作组在引力波事件GW190814中观测到的质量为2.50 \sim 2.67~M_\odot的致密天体,以及最近报告的在超新星遗迹HESS J1731-347中发现的一个质量和半径分别为M=0.77^+0.20_-0.17M_\odot和R=10.4^+0.86_-0.78 km的小质量致密天体,都对致密物质的研究提出了巨大的挑战。在中子星的内核部分,诸如超子之类的奇异自由度可能会出现从而形成超子星。本工作在密度依赖的相对论平均场(DDRMF)模型框架下研究由核子与轻子构成的中子星以及包含超子的超子星。采用目前常用的DDRMF参数研究了中子和超子星的质量、半径、潮汐形变等性质。发现,由DD-MEX, DD-MEX1, DD-MEX2, DD-MEXY和DD-LZ1参数组计算出的中子星的最大质量可以达到2.5 \sim 2.6~M_\odot,因为这几组参数能够得到很硬的状态方程,这是由它们在高密度时来自矢量势的强排斥贡献产生的。此外,通过研究壳层部分状态方程和核心部分状态方程对中子星性质的影响,我们发现来自HESS J1731-347的观测数据更倾向于较高对称能斜率L参数的壳层状态方程和较低L参数的核心状态方程,而且这样构造出的状态方程所得到的中子星的质量-半径关系也能符合NICER给出的PSR J0740+6620,PSR J0030+0451的限制以及来自GW170817事件的观测限制。在加入超子之后,超子星物质与中子星物质相比会变得较软,但是如果矢量介子的耦合常数很强的话,利用DDRMF模型也可以得到大质量超子星。

     

    Abstract: The neutron star as a supernova remnant is attracting high attention recently due to the gravitation wave detection and precise measurements about its mass and radius. In particular, the compact object with a mass of 2.50 \sim 2.67 \; M_\odot observed by LIGO Scientific and Virgo collaborations in GW190814, as well as the recent report of a light compact object with a mass and radius of M=0.77^+0.20_-0.17M_\odot and R=10.4^+0.86_-0.78 km within the supernova remnant HESS J1731-347, have posed a great challenge to the investigations into the supranuclear matter. In the inner core of a neutron star, the strangeness degrees of freedom, such as the hyperons, can be present to form a hyperon star. In this work, the neutron star consisting of nucleons and leptons, and the hyperonic star including the hyperons will be studied in the framework of the density-dependent relativistic mean-field (DDRMF) model. Some popular DDRMF parameterizations will be adopted to investigate the properties of nuclear matter and the mass, radius, tidal deformability, and other properties of neutron star and hyperonic stars. We find that the maximum masses of neutron star calculated by DD-MEX, DD-MEX1, DD-MEX2, DD-MEXY and DD-LZ1 sets can be around 2.5 \sim 2.6 \; M_\odot because they can produce quite stiff equations of state (EOSs) due to the strong repulsive contributions from vector potentials at high densities. Moreover, by investigating the influence of the crust EOS and core EOS on the neutron stars, we find that the observational data from HESS J1731-347 suggest the requirement of a crust EOS with a higher L parameter and a core EOS with a lower L parameter, and the M-R relations from the constructed EOSs can also be consistent with the observables of PSR J0740+6620, PSR J0030+0451 from NICER and the GW170817 event. With the inclusion of hyperons, the hyperonic star matter becomes softer compared to the neutron star matter, but the massive hyperonic star can also be obtained with DDRMF parameter sets if the vector meson coupling constants are strong.

     

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