标题： 等级合并星系中三黑洞系统的动力学 显示英文标题

标题： Dynamics of triple black hole systems in hierarchically merging massive galaxies

摘要： 具有恒星核球的星系普遍被观测到宿主超大质量黑洞（SMBH）。 因此，星系的等级合并应该会导致超大质量黑洞双星的形成。 旧且巨大的星系合并，伴随少量气体，促进了低密度核区的形成，在那里预期超大质量黑洞双星可以长时间存活。 如果双星寿命超过典型合并时间间隔，则三黑洞（BH）系统可能会形成。 我们通过计算一系列基于巨型椭圆星系物理动机的初始条件的三体轨道，来研究星系核区中紧密三-SMBH相遇的统计特性。 我们的模拟包括一个由恒星核球和暗物质晕组成的平滑背景势，由于引力辐射和恒星与暗物质的动力学摩擦引起的拖拽力，以及一个简单的描述SMBH加热和质量抛射下内密度分布随时间演化的模型。 我们发现，二元对在约85%的运行中因重复的近距离遭遇而合并，在约15%的情况下，一个新的偏心双星从第三个SMBH和双星残余物形成，并在运行时间内合并。 大约在40%的运行中，最轻的黑洞被留下在星系晕中漂移或完全逃离星系，但三个SMBH都逃逸的情况极为罕见。 这些三重系统通常会挖掘出质量亏损约为其总质量1到2倍的核心，这可能有助于解释一些质量较大的椭圆星系（如M87）中观察到的大核心。 运行中的高合并率、极高偏心率轨道的普遍存在以及近距离遭遇期间的引力辐射“尖峰”，可能会为未来的激光干涉仪空间天线（LISA）提供有趣信号。 显示英文摘要

摘要： Galaxies with stellar bulges are generically observed to host supermassive black holes (SMBHs). The hierarchical merging of galaxies should therefore lead to the formation of SMBH binaries. Merging of old massive galaxies with little gas promotes the formation of low-density nuclei where SMBH binaries are expected to survive over long times. If the binary lifetime exceeds the typical time between mergers, then triple black hole (BH) systems may form. We study the statistics of close triple-SMBH encounters in galactic nuclei by computing a series of 3-body orbits with physically-motivated initial conditions appropriate for giant elliptical galaxies. Our simulations include a smooth background potential consisting of a stellar bulge plus a dark matter halo, drag forces due to gravitational radiation and dynamical friction on the stars and dark matter, and a simple model of the time evolution of the inner density profile under heating and mass ejection by the SMBHs. We find that the binary pair coalesces as a result of repeated close encounters in ~85% of our runs, and in ~15% of cases a new eccentric binary forms from the third SMBH and binary remnant and coalesces during the run time. In about 40% of the runs the lightest BH is left wandering through the galactic halo or escapes the galaxy altogether, but escape of all three SMBHs is exceedingly rare. The triple systems typically scour out cores with mass deficits ~1-2 times their total mass, which can help to account for the large cores observed in some massive elliptical galaxies, such as M87. The high coalescence rate, prevalence of very high-eccentricity orbits, and gravitational radiation ``spikes'' during close encounters in our runs, may provide interesting signals for the future Laser Interferometer Space Antenna (LISA).