During the inspiral and merger of a binary black hole, gravitational radiation is emitted anisotropically due to asymmetries in the merger configuration. This anisotropic radiation leads to a gravitational wave kick, or recoil velocity, as large as ～4000 km s~(-1). We investigate the effect gravitational recoil has on the retention of intermediate-mass black holes (IMBHs) within the population of Galactic globular clusters by simulating the response of IMBHs to black hole mergers. Assuming that our current understanding of IMBH formation is correct and yields an IMBH seed in every globular cluster, we find a significant problem in retaining low-mass IMBHs (approx< 1000 M_☉) in the typical merger-rich globular cluster environment. Given a uniform black hole spin distribution and orientation and a stellar-mass black hole mass function generated in a low-metallicity system, we find that only three of the Milky Way globular clusters can retain an IMBH with an initial mass of 200 M_☉. Even if IMBHs have an initial mass of 1000 M_☉, only 60 would remain within Milky Way globular clusters, and each would reside only in the most massive clusters. Our calculations show that if there are black holes of mass M > 50 M_☉ in a cluster, repeated IMBH-black hole encounters will eventually eject a M = 1000 M_☉ IMBH with greater than 30% probability. As a consequence, a large population of rogue black holes may exist in our Milky Way halo. We briefly discuss the dynamical implications of this process and its possible connection to ultraluminous X-ray sources (ULXs).
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机译：在二值黑洞的吸积和合并过程中，由于合并配置中的不对称性，各向异性地发射了重力辐射。这种各向异性的辐射导致引力波反冲或反冲速度，高达〜4000 km s〜（-1）。我们通过模拟IMBHs对黑洞合并的反应，研究了重力反冲对银河系球状星团中的中等质量黑洞（IMBHs）的保留作用。假设我们对IMBH形成的当前理解是正确的，并且在每个球状星团中都产生了IMBH种子，我们发现在典型的富含并购的球状星团环境中保留低质量的IMBH（约<1000M_☉）存在一个重大问题。给定均匀的黑洞自旋分布和方向以及在低金属性系统中生成的恒星质量黑洞质量函数，我们发现只有三个银河系球状星团可以保留初始质量为200M_☉的IMBH。即使IMBH的初始质量为1000M_☉，在银河系球状星团中也将仅保留60个，而每个星团仅驻留在最大的星团中。我们的计算表明，如果在一个簇中存在质量M> 50M_☉的黑洞，则反复遇到IMBH-黑洞会最终以大于30％的概率弹出M = 1000M_☉IMBH。结果，在我们的银河系光晕中可能存在大量的流氓黑洞。我们简要讨论了此过程的动力学含义及其与超发光X射线源（ULXs）的可能联系。
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