paper

Repeated mergers and ejection of black holes within nuclear star clusters

arXiv:2006.01867 · doi:10.1093/mnras/staa2629

Abstract

Current stellar evolution models predict a dearth of black holes (BHs) with masses M and M, and intermediate-mass black holes (IMBHs; M) have not yet been detected beyond any reasonable doubt. A natural way to form massive BHs is through repeated mergers, detectable via gravitational wave emission with current LIGO/Virgo or future LISA and ET observations. Nuclear star clusters (NSCs) have masses and densities high enough to retain most of the merger products, which acquire a recoil kick at the moment of merger. We explore the possibility that IMBHs may be born as a result of repeated mergers in NSCs, and show how their formation pathways depend on the NSC mass and density, and BH spin distribution. We find that BHs in the pair-instability mass gap can be formed and observed by LIGO/Virgo, and show that the typical mass of the ejected massive BHs is -- M, with velocities of up to a few thousand km s. Eventually some of these IMBHs can become the seeds of supermassive BHs, observed today in the centers of galaxies. In dwarf galaxies, they could potentially solve the abundance, core-cusp, too-big-to-fail, ultra-faint, and baryon-fraction issues via plausible feedback scenarios.

arXiv comment15 pages, 10 figures, 1 table, accepted by MNRAS

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