arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2008.09839astro-ph.HEnucl-th
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低质量中子星的引力波星震学

Gravitational wave asteroseismology for low-mass neutron stars

Hajime Sotani

摘要:

利用以核饱和参数为特征的物态方程系统地研究了冷低质量中子星的基本($f$ -)模引力波,特别是着重研究了与第一压力($p_1$ -)模的避免交叉现象.我们发现中子星在避开的交点处的$f$模频率和平均密度可以表示为参数$η$的函数,该参数是核饱和参数的特定组合。由于这些关系,我们可以推导出经验公式,表示低质量中子星的$f$模式频率,其中心密度大于在避免交叉处的中子星,作为$η$和恒星平均密度$x$的平方根的函数。另一方面,我们还导出了一个经验公式,表示的$f$模式的频率的中子星,其中心密度小于中子星在避免交叉,作为一个函数的$x$独立于所采用的状态方程。此外,采用$x$作为$η$和$u_c$(恒星中心密度与饱和密度之比)的函数的经验公式,我们也可以将我们的$f$模频率的经验公式改写为$η$和$u_c$的函数.因此,通过观测一个质量或引力红移已知的低质量中子星的$f$模引力波,可以估算出$η$和$u_c$的值,这使我们能够严格地约束中子星物质的物态方程。

英文摘要:

The fundamental ($f$-) mode gravitational waves from cold low-mass neutron stars are systematically studied with various equations of state (EOSs) characterized by the nuclear saturation parameters, especially focusing on the phenomena of the avoided crossing with the first pressure ($p_1$-) mode. We find that the $f$-mode frequency and the average density for the neutron star at the avoided crossing can be expressed as a function of the parameter, $η$, which is the specific combination of the nuclear saturation parameters. Owing to these relations, we can derive the empirical formula expressing the $f$-mode frequency for a low-mass neutron star, whose central density is larger than that for the neutron star at the avoided crossing, as a function of $η$ and the square root of the stellar average density, $x$. On the other hand, we also derive the empirical formula expressing the $f$-mode frequency for a neutron star, whose central density is less than that for the neutron star at the avoided crossing, as a function of $x$ independently of the adopted EOS. Furthermore, adopting the empirical formula of $x$ as a function of $η$ and $u_c$, which is the ratio of the stellar central density to the saturation density, we can also rewrite our empirical formula for the $f$-mode frequency to a function of $η$ and $u_c$. So, by observing the $f$-mode gravitational wave from a low-mass neutron star, whose mass or gravitational redshift is known, one could evaluate the values of $η$ and $u_c$, which enables us to severely constrain the EOS for neutron star matter.

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