Abstract

While it is now clear from LIGO that stellar mass black hole (BH) binaries exist and merge, the existence of in-spiraling and merging supermassive black holes (SMBHs) has yet to be demonstrated. This workshop will address the open astrophysical questions regarding the precursors to SMBH binaries in the gravitational wave regime. Specifically, what are the rates at which binary SMBHs enter an evolutionary phase where their evolution is dominated by gravitational wave emission and what are the properties (masses, mass ratio, orbits, etc.) of those binaries? Answering these questions is critically important in planning for low-frequency GW observatories such as the Laser Space Interferometer Antenna (LISA) and pulsar timing arrays (PTAs). This workshop will address the evolution of SMBH pairs from the early stages of galaxy mergers, through binary formation and hardening, up to the gravitational wave regime. This includes formation of the first massive BHs, the frequency of galaxy mergers, supermassive black hole growth during galaxy mergers, and how the systems dynamically evolve from galaxy merger to BHs sinking into the galaxy center - addressed from both observational/experimental and theoretical perspectives.