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arXiv 2305.18522gr-qcastro-ph.HEhep-thnlin.CD
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缓慢旋转致密天体:Hartle-Thorne粒子测地线的不可积性

Slowly-rotating compact objects: the nonintegrability of Hartle-Thorne particle geodesics

Kyriakos Destounis, Kostas D. Kokkotas

AI总结:

本文系统研究缓慢旋转Hartle-Thorne时空中粒子轨道,发现共振附近形成Birkhoff岛及旋转曲线平台,证明一般测地线不可积,并指出该不可积性可能影响低质量X射线双星准周期振荡及致密天体参数估计。

摘要:

X射线天文学提供了关于活动星系核和X射线双星电磁辐射的信息。这些事件揭示了黑洞和恒星天体物理环境的细节,并帮助我们理解伽马射线暴。它们能够给出中子星最大质量的估计,并最终将有助于发现中子星的状态方程。因此,研究它们对于在结合多信使天体物理学时提高X射线天文学的产出至关重要。对于旋转中子星,场方程并不存在精确解。存在多种可以刻画相对论性恒星的致密天体近似解。其中研究最多的近似是Hartle-Thorne度规,它代表缓慢旋转的致密天体,如大质量恒星、白矮星和中子星。最近对该度规的光子轨道和阴影的研究表明,它在共振附近表现出混沌。在此,我们彻底研究了Hartle-Thorne时空中直至旋转二阶的粒子轨道。我们通过改变系统中涉及的所有参数,对有界运动进行了详尽分析。我们证明,被称为Birkhoff岛的混沌区域在共振附近形成,其中测地线的径向频率与极向频率之比(称为旋转数)在整个岛内是相同的。这导致在最显著的$2/3$共振期间旋转曲线中形成平台,从而证实了一般测地线是不可积的。我们测量了这些平台的宽度,并展示了每个参数如何影响它。当考虑混沌时,Hartle-Thorne度规的不可积性可能会影响低质量X射线双星的准周期振荡,并有可能改进对天体物理致密天体的质量、角动量和多极矩的估计。

英文摘要:

X-ray astronomy provides information regarding the electromagnetic emission of active galactic nuclei and X-ray binaries. These events provide details regarding the astrophysical environment of black holes and stars, and help us understand gamma-ray bursts. They produce estimates for the maximum mass of neutron stars and eventually will contribute to the discovery of their equation of state. Thus, it is crucial to study them in order to enhance the yield of X-ray astronomy when combined with multimessenger astrophysics. An exact solution of the field equations does not exist for rotating neutron stars. There exist a variety of approximate solutions for compact objects that may characterize relativistic stars. The most studied approximation is the Hartle-Thorne metric that represents slowly-rotating compact objects, like massive stars, white dwarfs and neutron stars. Recent investigations of photon orbits and shadows of such metric revealed that it exhibits chaos close to resonances. Here, we thoroughly investigate particle orbits around the Hartle-Thorne spacetime up to second order in rotation. We perform an exhaustive analysis of bound motion, by varying all parameters involved in the system. We demonstrate that chaotic regions, known as Birkhoff islands, form around resonances, where the ratio of the radial and polar frequency of geodesics, known as the rotation number, is shared throughout the island. This leads to the formation of plateaus in rotation curves during the most prominent $2/3$ resonance, which confirms that generic geodesics are nonintegrable. We measure their width and show how each parameter affects it. The nonintegrability of Hartle-Thorne metric may affect quasiperiodic oscillations of low-mass X-ray binaries, when chaos is taken into account, and might potentially improve estimates of mass, angular momentum and multipole moments of astrophysical compact objects.

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