Mass and rate of hierarchical black hole mergers in young, globular and nuclear star clusters

Understand

Hierarchical mergers are one of the distinctive signatures of binary black hole (BBH) formation through dynamical evolution.

• Here, we present a fast semi-analytic approach to simulate hierarchical mergers in nuclear star clusters (NSCs), globular clusters (GCs) and young star clusters (YSCs).
• Hierarchical mergers are more common in NSCs than they are in both GCs and YSCs, because of the different escape velocity.
• The mass distribution of hierarchical BBHs strongly depends on the properties of first-generation BBHs, such as their progenitor's metallicity.