Simulations Predict Intermediate-Mass Black Hole Formation in Globular Clusters

Intermediate-mass black holes (IMBHs) are those between 100 and 10 5 solar masses ( M ⨀ ); their formation process is debated. One potential origin is the growth of less massive black holes, by merging with stars and compact objects within globular clusters (GCs). However, previous simulations have indicated that this process only produces IMBHs <500 M ⨀ , before gravitational wave recoil ejects them from the GC. 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 ≳10 3 M ⨀ , which is sufficiently massive to be retained within the GC even with the expected gravitational wave recoil.