Browsing by Subject "galaxies: interactions"

This thesis presents the results from seventeen collisionless merger simulations of massive early-type galaxies in an effort to understand the coalescence of supermassive black holes (SMBHs) in the context of the Final Parsec Problem. A review of the properties of massive early-type galaxies and their SMBHs is presented alongside a discussion on SMBH binary coalescence to motivate the initial conditions used in the simulations. The effects of varying SMBH mass and stellar density profiles in the progenitor initial conditions on SMBH coalescence was investigated. Differing mass resolutions between the stellar particles and the SMBHs for each physical realisation were also tested. The simulations were performed on the supercomputers Puhti and Mahti at CSC, the Finnish IT Centre for Science. SMBH coalescence was found to only occur in mergers involving SMBH binaries of equal mass, with the most rapid coalescence observed in galaxies with a steep density profile. In particular, the eccentricity of the SMBH binary was observed to be crucial for coalescence: all simulations that coalesced displayed an orbital eccentricity in excess of e=0.7 for the majority of the time for which the binary was bound. Simulations of higher mass resolution were found to have an increased number of stellar particles able to positively interact with the SMBH binary to remove orbital energy and angular momentum, driving the binary to coalescence. The gravitational wave emission from an equal mass SMBH binary in the final stages before merging was calculated to be within the detection limits required for measurement by pulsar timing arrays. Mergers between galaxies of unequal mass SMBHs were unable to undergo coalescence irrespective of mass resolution or progenitor density profile, despite the binary in some of these simulations displaying a high orbital eccentricity. It was determined that the stellar particles interacting with the SMBH binary were unable to remove the required orbital energy and angular momentum to bring the SMBHs to within the separation required for efficient gravitational wave emission. A trend between increasing mass resolution and increasing number of stellar particles able to remove energy from the SMBH binary was observed across all the simulation suites. This observation is of paramount importance, as three-body interactions are essential in removing orbital energy and angular momentum from the SMBH binary, thus overcoming the Final Parsec Problem. As such, it is concluded that the Final Parsec Problem is a numerical artefact arising from insufficient mass resolution between the stellar particles and the SMBHs rather than a physical phenomenon.