http://arxiv.org/abs/2109.14612
The recent discovery of the binary black hole (BBH) merger event GW190521, between two black holes (BHs) of $\sim100M_\odot$, and as well as other massive BBH merger events involving BHs within the pair-instability supernova (PSN) mass gap have sparked widespread debate on the origin of such extreme gravitational-wave (GW) events. In this study, I investigate whether dynamical interactions in young massive clusters (YMCs) serves as a viable scenario for assembling PSN-gap BBH mergers. To that end, I explore a grid of 24 new evolutionary models of a representative YMC of initial mass $M_{\rm cl}=7.5\times10^4M_\odot$ ($N\approx1.28\times10^5$) and size $r_h=2$ pc, with all BH progenitor stars being initially in primordial binaries. All cluster models are evolved with the direct, relativistic N-body code NBODY7 incorporating up to date remnant formation, BH natal spin, and general-relativistic (GR) merger recoil schemes. The BBH mergers from these model cluster computations agree well with the GWTC-2 and GWTC-2.1 events’ masses and effective spin parameters. In particular, GW190521-like, i.e., $\sim200M_\odot$, low aligned spin events are produced via dynamical merger among BHs derived from star-star merger products. GW190403-like, i.e., PSN-gap, highly asymmetric and aligned events result from mergers involving BHs that are spun up via matter accretion or binary interaction. The resulting differential merger rate density within the PSN gap well accommodates that from GWTC-2. Particularly, the models well reproduce the LVK-estimated merger rate density of GW190521-like events. This study demonstrates that, subject to model uncertainties, the tandem of massive binary evolution and dynamical interactions in low metallicity YMCs in the Universe can plausibly produce GR mergers involving PSN-gap BHs and in rates consistent with that from to-date GW observations. [Abridged]
S. Banerjee
Fri, 1 Oct 21
48/65
Comments: 13 pages, 7 figures, 1 table (main text: 8 pages, 3 figures). Submitted. Comments are welcome