ECCENTRIC EVOLUTION OF SUPERMASSIVE BLACK HOLE BINARIES
ECCENTRIC EVOLUTION OF SUPERMASSIVE BLACK HOLE BINARIES
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DOI：
10.1088/2041-8205/731/1/l9
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发表时间：
2010-11
期刊：
影响因子：
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通讯作者：
M. Iwasawa;Sangyong An;T. Matsubayashi;Y. Funato;J. Makino
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文献类型：
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作者：
M. Iwasawa;Sangyong An;T. Matsubayashi;Y. Funato;J. Makino
在最近的数值模拟中，人们发现超大质量黑洞（SMBH）-中等质量黑洞（IMBH）双星的偏心率通过与恒星背景的相互作用而趋于一致。这种离心率的增加减少了双星通过引力辐射的合并时间尺度，使其值远低于哈勃时间。它也给出了偏心双星的存在，如在OJ 287的理论解释。在自洽N体模拟中，总是观察到这种偏心率的增加。另一方面，SMBH双星与场星的散射实验结果表明，它们的偏心率变化不大。这种差异使得N体模拟中SMBH双星的高偏心率无法解释。在这里，我们提出了一个恒星动力学机制，驱动具有大质量比的SMBH二进制的偏心率的增加。这涉及两个关键过程。第一种是在非轴对称势下的Kozai机制，它有效地使周围恒星的角动量随机化。另一种是选择性地喷射轨道相反的恒星。通过这两种机制，场星提取SMBH双星的轨道角动量。我们提出的机制导致大多数SMBH双星的离心率增加，导致通过引力波辐射的快速合并。我们的结果给出了“最后秒差距问题”的一个明确的解决方案。
In recent numerical simulations, it has been found that the eccentricity of supermassive black hole (SMBH)–intermediate black hole (IMBH) binaries grows toward unity through interactions with the stellar background. This increase of eccentricity reduces the merging timescale of the binary through the gravitational radiation to a value well below the Hubble time. It also gives a theoretical explanation of the existence of eccentric binaries such as that in OJ287. In self-consistent N-body simulations, this increase of eccentricity is always observed. On the other hand, the result of the scattering experiment between SMBH binaries and field stars indicated that the eccentricity dose not change significantly. This discrepancy leaves the high eccentricity of the SMBH binaries in N-body simulations unexplained. Here, we present a stellar-dynamical mechanism that drives the increase of the eccentricity of an SMBH binary with a large mass ratio. There are two key processes involved. The first one is the Kozai mechanism under a non-axisymmetric potential, which effectively randomizes the angular momenta of surrounding stars. The other is the selective ejection of stars with prograde orbits. Through these two mechanisms, field stars extract the orbital angular momentum of the SMBH binary. Our proposed mechanism causes the increase in the eccentricity of most of SMBH binaries, resulting in the rapid merger through gravitational wave radiation. Our result has given a definite solution to the “last-parsec problem.”