paper

Breaching the limit: formation of GW190521-like and IMBH mergers in young massive clusters

arXiv:2105.07003 · doi:10.3847/1538-4357/ac1419

Abstract

The LIGO-Virgo-Kagra collaboration (LVC) discovered recently GW190521, a gravitational wave (GW) source associated with the merger between two black holes (BHs) with mass M and M. GW190521 represents the first BH binary (BBH) merger with a primary mass falling in the "upper mass-gap" and the first leaving behind a M remnant. So far, the LVC reported the discovery of four further mergers having a total mass M, i.e. in the intermediate-mass black holes (IMBH) mass range. Here, we discuss results from a series of 80 -body simulations of young massive clusters (YMCs) that implement relativistic corrections to follow compact object mergers. We discover the development of a GW190521-like system as the result of a 3rd-generation merger, and four IMBH-BH mergers with total mass M. We show that these IMBH-BH mergers are low-frequency GW sources detectable with LISA and DECIGO out to redshift and , and we discuss how their detection could help unravelling IMBH natal spins. For the GW190521 test case, we show that the 3rd-generation merger remnant has a spin and effective spin parameter that matches the credible interval measured for GW190521 better than a simpler double merger and comparably to a single merger. Due to GW recoil kicks, we show that retaining the products of these mergers require birth-sites with escape velocities km s, values typically attained in galactic nuclei and massive clusters with steep density profiles.

23 pages, 11 figures, 2 tables, 2 Appendix. ApJ accepted

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