Stellar-mass black holes in young massive and open stellar clusters - IV. Updated stellar-evolutionary and black hole spin models and comparisons with the LIGO-Virgo O1/O2 merger-event data

I present a set of long-term, direct, relativistic many-body computations of model dense stellar clusters with up-to-date stellar-evolutionary, supernova (SN), and remnant natal-kick models, including pair instability and pulsation pair instability supernova (PSN and PPSN), using an updated version of NBODY7 N-body simulation program. The N-body model also includes stellar evolution-based natal spins of black holes (BHs) and treatments of binary black hole (BBH) mergers based on numerical relativity. These, for the first time in a direct N-body simulation, allow for second-generation BBH mergers. The set of 65 evolutionary models have initial masses 10(4)-10(5) M-circle dot, sizes 1-3 pc, metallicity 0.0001-0.02, with the massive stars in primordial binaries and they represent young massive clusters (YMC) and moderately massive open clusters (OC). Such models produce dynamically paired BBH mergers that agree well with the observed masses, mass ratios, effective spin parameters, and final spins of the LVC O1/O2 merger events, provided BHs are born with low or no spin but spin-up after undergoing a BBH merger or matter accretion on to it. In particular, the distinctly higher mass, effective spin parameter, and final spin of GW170729 merger event is naturally reproduced, as also the mass asymmetry of the O3 event GW190412. The computed models produce intermediate-mass, similar to 100 M-circle dot BBH mergers with primary mass within the 'PSN gap' and also yield mergers involving remnants in the 'mass gap'. They also suggest that YMCs and OCs produce persistent, Local-Universe GW sources detectable by LISA. Such clusters are also capable of producing eccentric LIGO-Virgo mergers.

Automated summary

This study conducted long-term, direct, relativistic many-body computations in model dense stellar clusters using up-to-date stellar-evolutionary, supernova, and remnant natal-kick models. The results showed that these models can produce dynamically paired black hole mergers that are in agreement with observations, while also suggesting that young massive clusters and moderately massive open clusters may produce detectable gravitational wave sources.