Black Hole Spin Distributions from Stellar Collisions in Young Massive Star Clusters*

This project investigates how stellar collisions in young massive star clusters imprint on black hole spin distributions and the broader implications for intermediate-mass black hole formation and r-process nucleosynthesis. The central hypothesis is that angular momentum transferred during stellar mergers substantially affects the spins of the resulting black holes, with some merger products evolving into collapsar-like objects that retain thick accretion disks and efficiently spin up.

Using 148 models generated with the Cluster Monte Carlo Code (CMC-COSMIC), the analysis focuses on collisions that lead to black hole formation, prioritizing statistically significant events with mass ratio q > 0.1 and grouping by interaction type. After identifying optimal candidates, detailed stellar structure and post-merger evolution are modeled with MESA to capture angular momentum injection and pre-collapse profiles most relevant for the natal spin. In the current dataset, main-sequence–giant encounters constitute roughly 85% of the significant black hole-forming collisions. Preliminary angular momentum estimates indicate substantial spin-up potential, and trends with mass ratio and stellar properties suggest strong correlations with the final black hole spin.This also has important implications for the dynamical formation of gravitational wave sources in clusters, similar to the many recent events detected by LIGO/VIRGO/Kagra.