Caltech/JPL Association for Gravitational-Wave Research Seminar

Gravitational waves will soon take us out of the realm of indirect observation of black holes and allow us to "see" them once and for all. By forcing black holes out of hiding, detectors such as LIGO and LISA will give us insight into the formation and demographics of these objects. Because of the weak nature of gravitational waves and the resultant challenges in data analysis, the success of these detectors depends in large part on a detailed understanding of the radiation sources. Mergers of black holes, on both stellar-mass and supermassive scales, are among the most important of such sources. Supermassive black holes lurk at most galactic centers, where they are likely to capture stellar-mass black holes onto close orbits that will lead to inspirals and mergers. These extreme mass ratio inspirals (EMRIs) can be formed by the tidal separation of black hole binaries, which will produce events with near-zero eccentricity in the LISA sensitivity band. The dense environments of galactic nuclei also foster close encounters between stellar-mass black hole binaries and stars. The black holes are often induced to merge, which makes galactic nuclei promising hosts of LIGO sources. Dynamically-triggered events such as these might be the dominant formation channel for mergers of black hole binaries, which would indicate that mergers will preferentially involve stellar-mass black holes at the upper end of the mass spectrum. I will present two formation channels for gravitational radiation sources: tidal separation of binaries by supermassive black holes and induced mergers of stellar-mass black holes in the centers of galaxies.