Repeated mergers of black hole binaries: implications for GW190521

Understand

The gravitational wave event GW190521 involves the merger of two black holes of $\sim 85\text{M}_\odot$ and $\sim 66\text{M}_\odot$ forming an intermediate-mass black hole (IMBH) of mass $\sim 142\text{M}_\odot$.

• Both progenitors are challenging to explain within standard stellar evolution as they are within the upper black-hole mass gap.
• We propose a dynamical formation pathway for this IMBH based on multiple mergers in the core of a globular cluster.
• We identify such scenarios from analysis of a set of 58 N-body simulations using \texttt{NBODY6-gpu}.