Speaker
Description
Binary stars orbiting supermassive black holes (MBHs) are relevant to several observable phenomena, including hypervelocity stars, X-ray binaries, and mergers of stars and compact objects; however, we know little about the properties of these binaries. We present two pertinent theoretical results. First, in a typical nuclear star cluster, up to ~50% of these binaries should shrink to near-contact separations. Contraction occurs through a combination of von-Ziepel-Lidov-Kozai oscillations, which excite a binary's eccentricity, and diffusive dynamical tides, which efficiently dissipate binding energy of orbits with very small pericenter separations. Second, during an active galactic nucleus (AGN) phase, many binaries in a nuclear star cluster will be separated by the Hills mechanism — one member will be ejected as a hypervelocity star, while the other will be implanted on a short-period orbit around the central black hole. This boost of disruptions is driven by the massive accretion disk powering the AGN; specifically, the disk torques binaries’ orbits around the MBH, often bringing them close enough to be separated by the black hole’s tidal potential. Finally, we consider how these results impact the expected population of stellar binaries in a given nuclear star cluster and the relevant observable phenomena mentioned above.
