MOCCA SURVEY Database I: Binary Black Hole Mergers from Globular Clusters with Intermediate Mass Black Holes

TL;DR

This study uses the MOCCA survey data to analyze how the presence and growth of intermediate mass black holes in globular clusters affect the formation and merger rates of stellar mass black hole binaries, revealing that massive IMBHs suppress binary mergers.

Contribution

It provides the first comprehensive analysis of the impact of IMBH formation and growth on black hole binary populations in globular clusters using large-scale simulation data.

Findings

Binary black hole merger rates align with predictions when IMBHs are less massive or form later.

Massive IMBHs (>10^4 solar masses) significantly reduce binary merger events.

Most merging black hole binaries escape before IMBH formation, affecting merger populations.

Abstract

The dynamical formation of black hole binaries in globular clusters that merge due to gravitational waves occurs more frequently in higher stellar density. Meanwhile, the probability to form intermediate mass black holes (IMBHs) also increases with the density. To explore the impact of the formation and growth of IMBHs on the population of stellar mass black hole binaries from globular clusters, we analyze the existing large survey of Monte-Carlo globular cluster simulation data (MOCCA SURVEY Database I). We show that the number of binary black hole mergers agrees with the prediction based on clusters' initial properties when the IMBH mass is not massive enough or the IMBH seed forms at a later time. However, binary black hole formation and subsequent merger events are significantly reduced compared to the prediction when the present-day IMBH mass is more massive than $\sim10^4 \rm M_{\odot}$ or the present-day IMBH mass exceeds about 1 per cent of cluster's initial total mass. By examining the maximum black hole mass in the system at the moment of black hole binary escaping, we find that $\sim$ 90 per cent of the merging binary black holes escape before the formation and growth of the IMBH. Furthermore, large fraction of stellar mass black holes are merged into the IMBH or escape as single black holes from globular clusters in cases of massive IMBHs, which can lead to the significant under-population of binary black holes merging with gravitational waves by a factor of 2 depending on the clusters' initial distributions.