Simulations predict intermediate-mass black hole formation in globular clusters

TL;DR

This study uses detailed star-by-star simulations to demonstrate that globular clusters can form intermediate-mass black holes exceeding 1000 solar masses through high-density star formation, overcoming previous mass ejection barriers.

Contribution

It introduces a new simulation approach showing that IMBHs can form directly during globular cluster formation, challenging prior models that limited IMBH growth.

Findings

High-density star formation leads to sufficient massive star mergers.

IMBHs with masses >1000 solar masses can be retained in GCs.

Previous models underestimated IMBH formation during GC formation.

Abstract

Intermediate-mass black holes (IMBHs) are those between 100 and 10$^5$ solar masses ($M_{\odot}$); their formation process is debated. One possible origin is the growth of less massive black holes (BHs) via mergers with stars and compact objects within globular clusters (GCs). However, previous simulations have indicated that this process only produces IMBHs $<500 M_{\odot}$ because the gravitational wave recoil ejects them when they merge with other BHs. We perform star-by-star simulations of GC formation, finding that high-density star formation in a GC's parent giant molecular cloud can produce sufficient mergers of massive stars to overcome that mass threshold. We conclude that GCs can form with IMBHs $\gtrsim 10^3 M_{\odot}$, which is sufficiently massive to be retained within the GC even with the expected gravitational wave recoil.