Effective no-hair relations for neutron stars and quark stars: Relativistic results
Effective no-hair relations for neutron stars and quark stars: Relativistic results
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中子星和夸克星的有效无毛关系：相对论结果
DOI：
10.1103/physrevd.89.124013
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发表时间：
2014
影响因子：
5
通讯作者：
T. Apostolatos
中科院分区：
文献类型：
--
作者：
Kent Yagi;K. Kyutoku;G. Pappas;N. Yunes;T. Apostolatos
天体物理学中的无电荷黑洞满足无毛关系，所有的多极矩都可以用它们的质量和自旋角动量来表示。本文研究了中子星和夸克星的多极矩之间可能存在的与它们的状态方程无关的非毛状关系。我们计算这些恒星的多极矩到十六极的顺序，通过构造均匀旋转和未磁化的恒星的爱因斯坦方程的解决方案。对于慢旋转恒星，我们构造恒星的解决方案，四次阶自旋在慢旋转展开，而对于快速旋转的恒星，我们解决爱因斯坦方程数值与LORENE和RNS代码。我们发现从这些数值解中提取的多极矩是一致的。我们证实了电流偶极与质量四极之间存在着近似状态方程独立的关系，对于快速旋转的中子星或夸克星，电流偶极与质量四极之间的关系不会发生破裂。我们进一步发现，电流八极矩和质量十六极矩与质量四极矩以近似状态方程无关的方式相关，在十六极矩的情况下恶化.我们所有的研究结果是在很好的协议与以前的工作，认为恒星的解决方案，在弱场膨胀的领导秩序。这里发现的自旋的四次曲线，缓慢旋转的解决方案，使我们能够估计系统误差的测量中子星星的质量和半径与未来的X射线观测，如NICER和LOFT。我们发现，这些四分之一的自旋条款上的四极矩和十六极矩和恒星偏心率的影响可能占主导地位的非常快速旋转的中子星的误差预算。这里发现的新的普遍关系应该有助于减少这种系统性错误。
Astrophysical charge-free black holes are known to satisfy no-hair relations through which all multipole moments can be specified in terms of just their mass and spin angular momentum. We here investigate the possible existence of no-hair-like relations among multipole moments for neutron stars and quark stars that are independent of their equation of state. We calculate the multipole moments of these stars up to hexadecapole order by constructing uniformly-rotating and unmagnetized stellar solutions to the Einstein equations. For slowly-rotating stars, we construct stellar solutions to quartic order in spin in a slow-rotation expansion, while for rapidly-rotating stars, we solve the Einstein equations numerically with the LORENE and RNS codes. We find that the multipole moments extracted from these numerical solutions are consistent with each other. We confirm that the current-dipole is related to the mass-quadrupole in an approximately equation of state independent fashion, which does not break for rapidly rotating neutron stars or quark stars. We further find that the current-octupole and the mass-hexadecapole moments are related to the mass-quadrupole in an approximately equation of state independent way to $\sim 10%$, worsening in the hexadecapole case. All of our findings are in good agreement with previous work that considered stellar solutions to leading-order in a weak-field expansion. The quartic in spin, slowly-rotating solutions found here allow us to estimate the systematic errors in the measurement of the neutron star's mass and radius with future X-ray observations, such as NICER and LOFT. We find that the effect of these quartic-in-spin terms on the quadrupole and hexadecapole moments and stellar eccentricity may dominate the error budget for very rapidly-rotating neutron stars. The new universal relations found here should help to reduce such systematic errors.