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arXiv 2301.08640astro-ph.HE
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追踪星系合并中SMBH和恒星物体的演化:一个多质量直接N体模型

Tracing the Evolution of SMBHs and Stellar Objects in Galaxy Mergers: An Multi-mass Direct N-body Model

Shuo Li, Shiyan Zhong, Peter Berczik, Rainer Spurzem, Xian Chen, F. K. Liu

摘要:

采用直接N体数值模拟方法,模拟了合并星系中两个超大质量黑洞与周围恒星的动力学协同演化。为了研究不同的恒星成分如何在合并过程中演变,我们生成演化的恒星分布与初始质量函数。对于一些罕见但有趣的事件,如主序星的潮汐破裂,低质量星、白矮星、中子星和恒星质量黑洞的坍缩,以及红巨星或渐近巨星分支星的部分潮汐破裂,人们也提出了特殊的方案。结果表明,束缚超大质量黑洞双星(SMBHB)的形成将提高SMBH对恒星天体的捕获率。与等恒星质量模型相比,多质量模型倾向于导致更高的分裂恒星的平均质量。大约一半的被捕获的主序星不会被SMBH的潮汐干扰,而是直接陷入SMBH,因为它们的恒星半径很小。另一方面,如果巨星离SMBH足够近,它们的外壳就可以被剥离。虽然大多数巨星的残余物可以在分裂后幸存下来,但一小部分仍然可以迅速或在许多轨道周期后坠入SMBH。我们的研究结果还表明,在合并开始时,致密星的质量分离显着,然后这种效果被破坏的两个SMBH形成一个绑定的二进制。

英文摘要:

By using direct N-body numerical simulations, we model the dynamical co-evolution of two supermassive black holes (SMBHs) and the surrounding stars in merging galaxies. In order to investigate how different stellar components evolve during the merger, we generate evolved stellar distributions with an initial mass function. Special schemes have also been developed to deal with some rare but interesting events, such as tidal disruption of main sequence stars, the plunge of low mass stars, white dwarfs, neutron stars and stellar mass black holes, and the partial tidal disruption of red giants or asymptotic giant branch stars. Our results indicate that the formation of a bound supermassive black hole binary (SMBHB) will enhance the capture rates of stellar objects by the SMBHs. Compared to the equal stellar mass model, the multi-mass model tends to result in a higher average mass of disrupted stars. Instead of being tidally disrupted by the SMBH, roughly half of the captured main sequence stars will directly plunge into the SMBH because of their small stellar radius. Giant stars, on the other hand, can be stripped of their envelopes if they are close enough to the SMBH. Though most remnants of the giant stars can survive after the disruption, a small fraction still could plunge into the SMBH quickly or after many orbital periods. Our results also indicate significant mass segregation of compact stars at the beginning of the merger, and then this effect is destroyed as the two SMBHs form a bound binary.

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