Branislav Avramov (Serbia)
b.avramov @ stud.uni-heidelberg.de
Dynamical evolution of supermassive black holes in galactic nuclei
Supermassive black holes (SMBH) reside in the center of the vast majority of galaxies. During galaxy mergers, SMBHs are brought close together to form gravitationally bound binary systems. If these systems are able to coalesce in a short enough period (less than Hubble time), they would be one of the most promising sources of gravitational radiation for the LISA (Laser Interferometer Space Antenna) mission. However, past theoretical models and numerical simulations have had trouble predicting the SMBH merger timescale, leading to the so called Final Parsec Problem (FPP). More specifically, the hardening of the binary would stall at parsec-scale separations, due to inefficient loss cone refilling and leading to merger timescales greater than the Hubble time. Recently, several new approaches have been proposed to resolve the FPP.
This project focuses on direct N-body simulations of a SMBH merger, under the assumption of a merger-induced triaxility of the merger remnant. This property allows for a very natural and efficient hardening rate of the SMBH binary, unlike idealized conditions of a spherically-symmetric remnant, thus avoiding the FPP. As a first step, a galaxy merger simulation consisting of about 6 million particles, which includes post-Newtonian effects up to 3.5 order and uses the PhiGPU-code, will be analysed. My work focuses on the 3-body encounters between the SMBH binary and stars in the loss cone. Before hardening due to gravitational wave emission becomes dominant, the energy exchange in these encounters is the dominant mechanism of energy loss for the SMBH binary. Namely, stars from the loss cone can gain kinetic energy from the binary via the gravitational slingshot effect, thus increasing the binding energy of the binary. My goal is to analyze the origin and properties of these stars which interact with the binary, as well as to explore certain energy discrepancies in the final phases of the merger, when the PN effects become significant.
Supervisor: Andreas Just (ARI)