超大质量黑洞周围偏心恒星轨道的一种新的长期不稳定性及其在银河系中心的应用
A New Secular Instability of Eccentric Stellar Disks Around Supermassive Black Holes, with Application to the Galactic Center
摘要：
我们发现了一种新的围绕超大质量黑洞的偏心恒星盘的长期不稳定性。我们发现，逆行岁差的恒星轨道，由于存在一个恒星尖点，诱导相干扭矩，放大偏差的个人轨道偏心率的平均值，从而驱动所有偏心率远离其初始值。我们调查的不稳定性，使用N体模拟，并表明，它可以驱动个人的轨道偏心率显着更高或更低的值的顺序上的岁差时间尺度。这种物理学与银河系中心有关，那里的大质量恒星很可能在SgrA* 黑洞周围的偏心盘中形成。我们发现，所观察到的双峰偏心率分布的盘星在银河系中心的分布是由偏心率不稳定性，并演示了如何在这样的磁盘的动力学演化的结果，它的几个恒星获得高（1-e < 0.1）的轨道偏心率。在这种高度偏心轨道上的双星会被SgrA* 黑洞潮汐干扰，可能会在黑洞附近产生S星，并在星系晕中产生高速星。
英文摘要：
We identify a new secular instability of eccentric stellar disks around supermassive black holes. We show that retrograde precession of the stellar orbits, due to the presence of a stellar cusp, induces coherent torques that amplify deviations of individual orbital eccentricities from the average, and thus drive all eccentricities away from their initial value. We investigate the instability using N-body simulations, and show that it can drive individual orbital eccentricities to significantly higher or lower values on the order of a precession time-scale. This physics is relevant for the Galactic center, where massive stars are likely to form in eccentric disks around the SgrA* black hole. We show that the observed bimodal eccentricity distribution of disk stars in the Galactic center is in good agreement with the distribution resulting from the eccentricity instability and demonstrate how the dynamical evolution of such a disk results in several of its stars acquiring high (1-e < 0.1) orbital eccentricity. Binary stars on such highly eccentric orbits would get tidally disrupted by the SgrA* black hole, possibly producing both S-stars near the black hole and high-velocity stars in the Galactic halo.
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