Nuclear symmetry energy and the r-mode instability of neutron stars
Nuclear symmetry energy and the r-mode instability of neutron stars
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DOI：
10.1103/physrevc.85.045808
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发表时间：
2012-02
影响因子：
3.1
通讯作者：
I. Vidaña
中科院分区：
文献类型：
--
作者：
I. Vidaña
分析了对称性能量斜率参数L对中子星模式不稳定性的影响。我们的研究是使用核物态方程的微观和唯象方法来进行的。微观模型包括Brueckner-Hartree-Fock近似，著名的Akmal、Pandharipande和RavenHall变分状态方程，以及最近辅助场扩散蒙特卡罗计算的参数化。对于唯象方法，我们使用了几种Skyrme力和相对论平均场模型。我们的结果表明，对于那些给出较大值$L$的模型，{it r}模不稳定性区域较小。这是因为体粘性和剪切粘性都随着L的增大而增大，因此，对于L越大的模型，模式的减振效果越好。我们还证明了在每个密度下，这两种粘度对$L的依赖关系可以用简单的幂函数来描述，即：{xi=A_{\xi}L^{B_xi}}和{eta=A_{\eta}L^{B_\xi}$。根据测量的低质量X射线双星4U1608-52中脉冲星的自旋频率和估计的核心温度，我们得出结论：如果假设这个天体在不稳定区之外，它的半径在11.5-12$($11.5-13$)公里范围内，它的质量为$1.4M_\ODOT$($2M_\ODOT$)，则观测数据似乎倾向于$L$大于$\sim 50$MeV的值。在这个范围之外，不可能从这颗脉冲星得出任何关于$L$的结论。
We analyze the role of the symmetry energy slope parameter $L$ on the {\it r}-mode instability of neutron stars. Our study is performed using both microscopic and phenomenological approaches of the nuclear equation of state. The microscopic ones include the Brueckner--Hartree--Fock approximation, the well known variational equation of state of Akmal, Pandharipande and Ravenhall, and a parametrization of recent Auxiliary Field Diffusion Monte Carlo calculations. For the phenomenological approaches, we use several Skyrme forces and relativisic mean field models. Our results show that the {\it r}-mode instability region is smaller for those models which give larger values of $L$. The reason is that both bulk ($\xi$) and shear ($\eta$) viscosities increase with $L$ and, therefore, the damping of the mode is more efficient for the models with larger $L$. We show also that the dependence of both viscosities on $L$ can be described at each density by simple power-laws of the type $\xi=A_{\xi}L^{B_\xi}$ and $\eta=A_{\eta}L^{B_\eta}$. Using the measured spin frequency and the estimated core temperature of the pulsar in the low-mass X-ray binary 4U 1608-52, we conclude that observational data seem to favor values of $L$ larger than $\sim 50$ MeV if this object is assumed to be outside the instability region, its radius is in the range $11.5-12$($11.5-13$) km, and its mass $1.4M_\odot$($2M_\odot$). Outside this range it is not possible to draw any conclusion on $L$ from this pulsar.