Abstract

Contributed Talk - Splinter StarClusters   (MW-2050)

Stellar-mass black holes in young massive and open stellar clusters: comparisons with the latest gravitational-wave event population and Gaia compact binaries

Sambaran Banerjee
University of Bonn

Gravitational-wave (GW) detections by the LIGO-Virgo-KAGRA (LVK) observatories suggest multiple formation channels for GW compact binary mergers. Here I assess the role of young massive clusters (YMCs) evolving into old open clusters (OCs) in forming the GW merger population. An unprecedented complete, detailed grid of 90 N-body evolutionary model star clusters, spanning initial masses of 10^4 Msun-10^5 Msun, half-mass radii of 1-3 pc, and metallicities between 0.0002-0.02, is computed with the direct, post-Newtonian N-body code NBODY7. The N-body simulations include primordial binaries, delayed stellar-remnant model forming black holes (BH) and neutron stars, BH spin prescriptions, and GW recoil kicks, and they are evolved until BH depletion -- typically, up to a few to 10 Gyr. Most GW mergers from the cluster models are dynamically assembled binary black holes (BBHs) that merge within their host clusters. Merger mass ratios reach down to 0.1-0.2 despite an overall bias toward nearly symmetric pairs. The computed mergers reproduce some of the key features of the latest observed GW event catalogue, including asymmetric low-mass mergers, misaligned events among highly spinning, massive BHs, and an excess of 30Msun primaries. The model merger rate density accounts for 25%-33% of the observed rate; it increases with redshift somewhat faster than the cosmic star formation, consistently with LVK's inferences. The model effective spin distribution is positive-biased at zero redshift and broadens with redshift, as observed. The models yield field BH- and NS-main sequence star binaries with parameters consistent with the Gaia-discovered compact remnant candidates. Reference: Banerjee, S., arXiv:2602.09694.