Dynamical Formation of Merging Stellar-Mass Binary Black Holes

Abstract

The astrophysical origin of black hole mergers is one of the most important outstanding questions in gravitational wave astronomy. How do black holes find each other in vast space, form binaries, and get so close to one another that gravitational wave emission can successfully merge them within the present age of the universe? In this chapter we review the dynamical formation channel, where the binary separation is reduced by dynamical processes. These processes are important for mergers in dense stellar clusters, galactic nuclei, mergers in supermassive black hole accretion disks, and mergers in stellar triple and quadruple systems and possibly in the dark matter halo. We introduce a unified framework to interpret the theoretical expectations on the characteristics of these merging binaries such as their gravitational wave frequency, eccentricity, mass, and spins to identify these gravitational wave source populations in merger catalogs. For dynamical merger pathways, we show that GW source catalogs carry information on the escape velocity of the host environment.