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arXiv 2001.02231astro-ph.GAastro-ph.HE
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恒星背景下大质量黑洞双星的偏心率演化

On the eccentricity evolution of massive black hole binaries in stellar backgrounds

Matteo Bonetti, Alexander Rasskazov, Alberto Sesana, Massimo Dotti, Francesco Haardt, Nathan W. C. Leigh, Manuel Arca Sedda, Giacomo Fragione, Elena Rossi

摘要:

利用三体散射实验研究了偏心大质量黑洞双星与非束缚星相互作用的动力学演化。与以前的研究相比,我们将调查扩展到$q=m_2/m_1=10^{-4}$的MBHB质量比,其中$m_1$和$m_2$分别是初级和次级孔的质量。与从更高质量比的简单外推相反,我们发现对于$q\lesssim 10^{-3}$,偏心增长率变为负值,即,二进制{ \it循环出现}收缩。这种行为是由于在亚稳的反向旋转轨道上捕获的相互作用恒星的子集;这些恒星倾向于从双星中提取角动量,促进$q>10^{-3}$的偏心率增长,但倾向于将角动量注入双星中,驱动它朝向$q<10^{-3}$的圆化。这种行为的物理起源需要对这一恒星子集的轨道进行详细研究,目前正在调查中。我们的发现可能会对中间MBH(IMBH)螺旋吸入MBH(例如,一个假定的$10^3\rm M_{\odot}$黑洞螺旋吸入SgrA $^*$)产生重要影响。

英文摘要:

We study the dynamical evolution of eccentric massive black hole binaries (MBHBs) interacting with unbound stars by means of an extensive set of three body scattering experiments. Compared to previous studies, we extend the investigation down to a MBHB mass ratio of $q=m_2/m_1=10^{-4}$, where $m_1$ and $m_2$ are the masses of the primary and secondary hole respectively. Contrary to a simple extrapolation from higher mass ratios, we find that for $q\lesssim 10^{-3}$ the eccentricity growth rate becomes negative, i.e., the binary {\it circularises} as it shrinks. This behaviour is due to the subset of interacting stars captured in metastable counter-rotating orbits; those stars tend to extract angular momentum from the binary, promoting eccentricity growth for $q>10^{-3}$, but tend to inject angular momentum into the binary driving it towards circularisation for $q<10^{-3}$. The physical origin of this behaviour requires a detailed study of the orbits of this subset of stars and is currently under investigation. Our findings might have important consequences for intermediate MBHs (IMBHs) inspiralling onto MBHs (e.g. a putative $10^3\rm M_{\odot}$ black hole inspiralling onto SgrA$^*$).

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