Tidal capture of stars by supermassive black holes: implications for periodic nuclear transients and quasi-periodic eruptions
Tidal capture of stars by supermassive black holes: implications for periodic nuclear transients and quasi-periodic eruptions
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超大质量黑洞对恒星的潮汐捕获：对周期性核瞬变和准周期性喷发的影响
DOI：
10.1093/mnrasl/slad001
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发表时间：
2023
影响因子：
--
通讯作者：
Coughlin, Eric R.
中科院分区：
文献类型：
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作者：
Cufari, M.;Nixon, C. J.;Coughlin, Eric R.
坠入星系中心的恒星会受到超大质量黑洞（SMBH）的潮汐扰动，距离越近，扰动就会越大。激发这些潮汐是以牺牲恒星的轨道能量为代价的，这导致了一个天真的结论：较小的近心（即恒星和超大黑洞之间的接触更近）总是会产生一颗与超大黑洞结合更紧密的恒星。然而，一旦近心距离足够小，恒星被部分破坏，恒星损失的质量的形态不对称性就会导致幸存核心的轨道能量增加，导致其被超大质量黑洞抛射——而不是捕获。使用平滑粒子流体动力学模拟，我们表明潮汐激发和不对称质量损失这两种效应的结合导致恒星结合能的潮汐损失的最大能量，该能量明显小于总恒星结合能的理论最大值。这一结果意味着，在短周期轨道（≲几年）上多次（≳10）次被SMBH部分破坏的恒星，正如被用来解释周期性核瞬变ASASSN-14ko和准周期喷发的那样，必须通过潮汐捕获以外的机制与SMBH结合，例如动态交换（即希尔斯捕获）。
Stars that plunge into the centre of a galaxy are tidally perturbed by a supermassive black hole (SMBH), with closer encounters resulting in larger perturbations. Exciting these tides comes at the expense of the star’s orbital energy, which leads to the naive conclusion that a smaller pericentre (i.e. a closer encounter between the star and SMBH) always yields a more tightly bound star to the SMBH. However, once the pericentre distance is small enough that the star is partially disrupted, morphological asymmetries in the mass lost by the star can yield anincreasein the orbital energy of the surviving core, resulting in its ejection – not capture – by the SMBH. Using smoothed particle hydrodynamics simulations, we show that the combination of these two effects – tidal excitation and asymmetric mass-loss – results in a maximum amount of energy lost through tides ofof the binding energy of the star, which is significantly smaller than the theoretical maximum of the total stellar binding energy. This result implies that stars that are repeatedly partially disrupted by SMBHs many (≳10) times on short-period orbits (≲few years), as has been invoked to explain the periodic nuclear transient ASASSN-14ko and quasi-periodic eruptions, must be bound to the SMBH through a mechanism other than tidal capture, such as a dynamical exchange (i.e. Hills capture).