超高速恒星S5-HVS1的前伴星
The former companion of the hyper-velocity star S5-HVS1
摘要：
超高速恒星S5-HVS 1，在500万年前以1800 km/s的速度从银河系中心喷射出来，很可能是由超大质量黑洞SgrA* 对紧密双星的潮汐分裂产生的。采用蒙特卡罗方法，我们表明，前伴星S5-HVS 1可能是一个主序星之间的1.2和6个太阳质量和被捕获到一个高度偏心的轨道，近心距离在1-10 AU和半长轴约$10^3$ AU。然后我们探索被捕获的恒星的命运。我们发现，当近心距离小于3AU时，潮汐激发的恒星振荡模所沉积的热量会导致失控破裂。在过去的500万年里，它的角动量已经被轨道弛豫显著地改变，这可能会随机地将近心向内驱动到3AU以下，并导致潮汐中断。我们发现总体生存概率在5%到50%之间，具体取决于捕获恒星近距离环境中的局部弛豫时间以及捕获时的初始近心点。幸存恒星的近心距离已经迁移到10-100 AU，使其成为S星团中最极端的成员。从S5-HVS 1类恒星的抛射率，我们估计目前可能有几颗恒星处于这种高度偏心的轨道上。它们应该可以被引力仪器和未来的超大望远镜探测到（通常Ks < 18.5等），因此提供了一个非凡的探测SgrA* 的自旋。
英文摘要：
The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Center at 1800 km/s, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 solar masses and was captured into a highly eccentric orbit with pericenter distance in the range 1-10 AU and semimajor axis about $10^3$ AU. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericenter distance is smaller than about 3 AU. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericenter inwards below 3 AU and cause tidal disruption. We find an overall survival probability in the range 5% to 50%, depending on the local relaxation time in the close environment of the captured star, and the initial pericenter at capture. The pericenter distance of the surviving star has migrated to 10-100 AU, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically Ks < 18.5 mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.
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