Abstract
"Detecting low-frequency gravitational waves (GWs) from binary supermassive black holes
(SMBHs), from missions such as the Laser Interferometer Space Antenna (LISA) and the
Pulsar Timing Array (PTA) will constrain the physics of SMBHs, the formation and evo-
lution of binary SMBHs, and the SMBH-galaxy connection.
This thesis, comprised of three publications, investigates the interplay of binary SMBH
dynamics in stellar environments.
The first publication addresses variation in the merger time-scale of SMBHs in galaxy
mergers. At typical resolutions for contemporary studies the bound eccentricity of the
SMBH binary can vary significantly. I classify this, for the first time, as a stochastic pro-
cess resulting in substantial variation in the merger timescale. This suggests that some of
the uncertainty in low-frequency GW rates is due to insufficient numerical resolution.
The second publication addresses the formation of the largest observed galactic cores in
massive elliptical galaxies, in particular A2261-BCG. I explore three scenarios for cen-
tral core formation in massive elliptical galaxies: ‘binary scouring’, ‘tidal deposition’
and ‘gravitational wave induced recoil’. I find that I can only explain the large surface
brightness core of A2261-BCG with a combination of a major merger, followed by the
subsequent GW recoil of its SMBH, which acts to grow the core size. The same model
can also explain the bright ‘knots’ observed in the core region of A2261-BCG.
The third publication investigates the formation of counter-rotating binaries, which are
prone to increasing eccentricity, leading to very eccentric binaries on the onset of GW
emission. I show that the origin of this orbital plane flip lies in the triaxiality of the
merger remnant, a natural consequence of a galaxy merger, and is affected by the rotation
of the host system.
This thesis serves to provide a better insight into the interplay between binary SMBHs
and their stellar environments."