Massive Stellar Triples Leading to Sequential Binary Black Hole Mergers in the Field

Stellar triples with massive stellar components are common and can lead to sequential binary black hole mergers. Here we outline the evolution toward these sequential mergers and explore these events in the context of gravitational-wave astronomy and the pair-instability mass gap. We find that binary black hole mergers in the pair-instability mass gap can be of triple origin and therefore are not exclusively formed in dense dynamical environments. We discuss the sequential merger scenario in the context of the most massive gravitational-wave sources detected to date: GW170729 and GW190521. We propose that the progenitor of GW170729 is a low-metallicity field triple. We support the premise that GW190521 could not have been formed in the field. We conclude that triple stellar evolution is fundamental to the understanding of gravitational-wave sources and likely other energetic transients as well.

Automated summary

This study explores the evolution of stellar triples with massive components leading to sequential binary black hole mergers, suggesting that these mergers can also occur outside of dense dynamical environments. The research also analyzes the evolution of two gravitational-wave sources, GW170729 and GW190521, proposing that the former originates from a low-metallicity field triple and arguing against the latter being formed in the field. In conclusion, the study emphasizes the importance of triple stellar evolution in understanding gravitational wave sources and other energetic transients.