Stellar-mass black holes in young massive and open stellar clusters and their role in gravitational-wave generation

Stellar-remnant black holes (BH) in dense stellar clusters have always drawn attention due to their potential in a number of phenomena, especially the dynamical formation of binary black holes (BBH), which potentially coalesce via gravitational-wave radiation. This study presents a preliminary set of evolutionary models of compact stellar clusters with initial masses ranging over 1.0 x 10(4)-5.0 x 10(4) M-circle dot, and half-mass radius of 2 or 1 pc, which is typical for young massive and starburst clusters. They have metallicities between 0.05 Z(circle dot) and Z circle dot. Including contemporary schemes for stellar wind and remnant formation, such model clusters are evolved, for the first time, using the state-of-the-art direct N-body evolution program NBODY7, until their dissolution or at least for 10 Gyr. That way, a self-regulatory behaviour in the effects of dynamical interactions among the BHs is demonstrated. In contrast to earlier studies, the BBH coalescences obtained in these models show a prominence in triple-mediated coalescences while being bound to the clusters, compared to those occurring among the BBHs that are dynamically ejected from the clusters. A broader mass spectrum of the BHs and lower escape velocities of the clusters explored here might cause this difference, which is yet to be fully understood. A mong the BBH coalescences obtained here, there are ones that resemble the detected GW151226, LVT151012 and GW150914 events and also ones that are even more massive. A preliminary estimate suggestsfew 10-100s of BBH coalescences per year, originating due to dynamics in stellar clusters that can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) at its design sensitivity.