On the orbital evolution of supermassive black hole binaries with circumbinary accretion discs
On the orbital evolution of supermassive black hole binaries with circumbinary accretion discs
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DOI：
10.1093/mnras/stx1130
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发表时间：
2017-03
影响因子：
4.8
通讯作者：
Yi-Lei Tang;A. MacFadyen;Z. Haiman
中科院分区：
文献类型：
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作者：
Yi-Lei Tang;A. MacFadyen;Z. Haiman
气态环双星吸积盘为星系核中超大质量黑洞的合并提供了一种很有前途的机制。我们测量的扭矩施加在吸积SMBH二进制，使用二维，等温，移动网格，粘性流体动力学模拟的circumbinary吸积盘。我们的计算域包括整个内部区域的circumbinary磁盘与个别黑洞（BH）包括网格上的点质量和水槽处方模型吸积到每个BH。每个黑洞都有自己清晰的吸积盘（minidisks）。我们探索了一系列的质量去除率的水槽处方去除气体的中心区域的minidisks。我们发现，施加在二进制的扭矩主要是重力，并占主导地位的气体轨道密切落后和领先的个人BH。来自更远的扭曲的环双星盘和来自角动量的直接吸积的扭矩是次主导的。扭矩是敏感的汇处方：较慢的汇导致更多的气体积累附近的BH和更多的负扭矩，驱动的双合并更快。对于更快的下沉，扭矩的负值较小，最终变为正值（对于非物理快速下沉）。当minidisces被建模为标准的阿尔法光盘，我们的结果是不敏感的下沉半径的选择。将模拟缩放到双胞胎轨道周期tbin = 1 yr，背景盘吸积率Mdot = 0.3MEdd（以埃丁顿单位表示），双胞胎的螺旋时间尺度为3X10^6年，无论SMBH质量如何。对于总质量小于10^7 Msun的双星，这比单独由引力波辐射引起的螺旋上升时间要短，这意味着气盘将对SMBH双星的数量产生重大影响，并可能影响脉冲星定时阵列的引力波信号。
Gaseous circumbinary accretion discs provide a promising mechanism to facilitate the mergers of supermassive black holes (SMBHs) in galactic nuclei. We measure the torques exerted on accreting SMBH binaries, using 2D, isothermal, moving-mesh, viscous hydrodynamical simulations of circumbinary accretion discs. Our computational domain includes the entire inner region of the circumbinary disk with the individual black holes (BHs) included as point masses on the grid and a sink prescription to model accretion onto each BH. The BHs each acquire their own well-resolved accretion discs ("minidiscs"). We explore a range of mass removal rates for the sink prescription removing gas from the central regions of the minidiscs. We find that the torque exerted on the binary is primarily gravitational, and dominated by the gas orbiting close behind and ahead of the individual BHs. The torques from the distorted circumbinary disc farther out and from the direct accretion of angular momentum are subdominant. The torques are sensitive to the sink prescription: slower sinks result in more gas accumulating near the BHs and more negative torques, driving the binary to merger more rapidly. For faster sinks, the torques are less negative and eventually turn positive (for unphysically fast sinks). When the minidiscs are modeled as standard alpha discs, our results are insensitive to the choice of sink radius. Scaling the simulations to a binary orbital period tbin = 1yr and background disc accretion rate Mdot = 0.3MEdd in Eddington units, the binary inspirals on a timescale of 3X10^6 years, irrespective of the SMBH masses. For binaries with total mass <10^7Msun, this is shorter than the inspiral time due to gravitational wave (GW) emission alone, implying that gas discs will have a significant impact on the SMBH binary population and can affect the GW signal for Pulsar Timing Arrays.