Ph.D Thesis
Ph.D Student Meiron Yohai The Stellar Kinematic Signature of Supermassive Black Hole Binaries Department of Physics Professor Ari Laor

Abstract

Supermassive black holes are likely to exist at the centres of most galaxies. Although their masses can reach ten billion times the mass of our Sun, they are not intrinsically luminous and their physical size is too small to resolve in cosmological distances; thus, they could only be detected in indirectly. Supermassive black holes interact with the stellar population in complex and intricate ways, and their imprint on their host galaxies goes beyond their radius of gravitational influence (where their mass dominates the gravitational potential, rather than the mass of stars). The topics discussed in this work include the evolution and the kinematic signature of supermassive black hole binaries, that form as a result of galactic collisions; and the coevolution of the black hole and its galaxy, that leads to correlations between the mass of the former and various parameters of the latter. I showed that black hole binaries, if present, could be detected through a kinematic signature in stars at the most inner regions of the galaxy; the most important features of that signature are a torus of stars rotating in the opposite direction with respect to stars further out, and a drop in velocity dispersion very close to the centre. Using a simulation technique based on conservation laws, I also showed that the rate of binary eccentricity growth during minor mergers is very high and could lead to coalescence in less than the Hubble time (of about ten billion years) and thus to a burst of gravitational radiation, that could be detected using future space-based detectors. Additionally, I showed the existence of a proportionality relation between the black hole mass and the momentum parameter of its host galaxy, which is proportional to the mass of the spheroidal component times the velocity dispersion of stars in it.