Mergers of Supermassive Black Hole Binaries in Gas-rich Environments: Models of Event Rates and Electromagnetic Signatures

摘要: Supermassive black holes permeate the observable Universe, residing in the nuclei of all or nearly all nearby massive galaxies and powering luminous quasars as far as ten billion light years away. These monstrous objects must grow through a combination of gas accretion and mergers of less massive black holes. The direct detection of the mergers by future gravitational-wave detectors will be a momentous scientific achievement, providing tests of general relativity and revealing the cosmic evolution of supermassive black holes. An additional—and arguably equally rewarding—challenge is the concomitant observation of merging supermassive black holes with both gravitational and electromagneticwaves. Such synergistic,“multi-messenger” studies can probe the expansion history of the Universe and shed light on the details of accretion astrophysics.