ACCRETION AND ORBITAL INSPIRAL IN GAS-ASSISTED SUPERMASSIVE BLACK HOLE BINARY MERGERS
ACCRETION AND ORBITAL INSPIRAL IN GAS-ASSISTED SUPERMASSIVE BLACK HOLE BINARY MERGERS
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气体辅助超大质量黑洞双星合并中的吸积和轨道吸气
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发表时间：
2016
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通讯作者：
R. Rafikov
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作者：
R. Rafikov
许多星系的中心都有超大质量黑洞（SMBH）。它们与周围气体的相互作用导致了角动量的吸积和交换，从而促进了双星的螺旋上升。在这里，我们探讨了这两个过程之间的非平凡耦合，并分析了外部提供的环双星盘的全局属性取决于二进制吸积率。通过制定我们的结果在由内部应力驱动的角动量通量，我们提出了一个非常简单的分类可能的全球磁盘结构，这不同于标准的常数吸积盘解决方案。双星潮汐对吸积的抑制，导致了内部盘中大量的物质积累，加速了双星的螺旋上升。我们表明，一旦磁盘区域强烈扰动的粘性传输的潮汐扭矩超过二进制半长轴，二进制可以合并在小于其质量倍增时间，由于吸积。因此，与由恒星散射驱动的吸气不同，即使双星被嵌入相对低质量的盘（低于其自身质量）中，气体辅助的合并也可以发生。这对于解决SMBH双星的“最后秒差距”问题和理解宇宙中强大的引力波源是重要的。我们认为，在最近的一些模拟中发现的双星吸积的增强不能持续很长一段时间，不应该影响长期的轨道螺旋。我们还回顾了现有的模拟SMBH二进制磁盘耦合，并提出了一个数值设置，这是特别适合于验证我们的理论预测。
Many galaxies are expected to harbor binary supermassive black holes (SMBHs) in their centers. Their interaction with the surrounding gas results in the accretion and exchange of angular momentum via tidal torques, facilitating binary inspiral. Here, we explore the non-trivial coupling between these two processes and analyze how the global properties of externally supplied circumbinary disks depend on the binary accretion rate. By formulating our results in terms of the angular momentum flux driven by internal stresses, we come up with a very simple classification of the possible global disk structures, which differ from the standard constant accretion disk solution. The suppression of accretion by the binary tides, leading to a significant mass accumulation in the inner disk, accelerates binary inspiral. We show that once the disk region strongly perturbed by the viscously transmitted tidal torque exceeds the binary semimajor axis, the binary can merge in less than its mass-doubling time due to accretion. Thus, unlike the inspirals driven by stellar scattering, the gas-assisted merger can occur even if the binary is embedded in a relatively low-mass disk (lower than its own mass). This is important for resolving the “last parsec” problem for SMBH binaries and understanding powerful gravitational wave sources in the universe. We argue that the enhancement of accretion by the binary found in some recent simulations cannot persist for a long time and should not affect the long-term orbital inspiral. We also review existing simulations of SMBH binary–disk coupling and propose a numerical setup which is particularly well suited to verifying our theoretical predictions.