Black Hole Mergers and Their Electromagnetic Counterparts

Abstract

Over the past ten years it has become increasingly clear that most, if not all, galaxies have super-massive black holes lurking in their cores. The implications for this are large as they not only have significant effects on the host galaxies, far beyond what would have been naively expected, but would provide several significant gravitational wave sources to the Laser Interferometer Space Antenna (LISA). This thesis is primarily concerned with these gravitational wave sources and the possible electromagnetic counterparts. In particular, when two galaxies merge, it leads to the ultimate merger of their individual SMBHs. If gas is present near the time of merger a circumbinary disk forms around the binary. By assuming the disk is pressureless, and looking at the limits of this approximation, in Chapter 2 we develop an analytic theory of the reaction of such a gaseous disk to the gravitational wave mass loss and recoil kicks which occur during a SMBH merger. However, to understand the effects of finite pressure, in Chapter 3 we develop a one-dimensional hydrodynamic code. The efficiency of the code and the power of the analytic solution allow us to explain the entirety of possible reactions. These results are also favorably compared with far more complicated 3D relativistic magneto-hydrodynamics simulations. LISA will not see only the mergers of two SMBHs, it would also see the inspirals of stellar-mass objects into a SMBH. In Chapter 4 we discuss a new channel of formation of these extreme mass ratio inspirals (EMRIs). This new channel of EMRI formation is rich physically and, in particular, almost always requiring either the Kozai mechanism or an as-of-yet unnoticed phenomenon which we dub the reverse Kozai mechanism. We find that this channel of EMRI formation produces modest numbers of EMRIs when compared to the primary channel of EMRI formation, which, under optimistic detection scenarios for the most recent LISA design, results in the plausible detection of several. Finally, an unrelated project that considers solving the self-similar Type-II strong-shock problem in slightly asymmetric media is given in Chapter 5. We show that the results can even be applied to explosions along weak discontinuities in the density.