The Origin of LIGO Sources: Understanding The Formation Channels of Stellar Mass Binary Black Holes
Physical and Biological Sciences
Physics (Astrophysics)
The era of multi-messenger astronomy commenced on September 14, 2015 with the detection of a binary black hole (BBH) merger by the Laser Interferometer Gravitational-Wave Observatory (LIGO). Such an event has been predicted for a century but the origin of these signals has been debated ever since. Currently, there are two proposed formation channels for LIGO BBH signals: formation through natural stellar evolution and formation through dynamical assembly in dense stellar systems. Astronomers postulate that a key marker to differentiate between these two channels is the spins of the BHs. Currently, LIGO measures the spin of BHs through a parameter called χeff. The premise that different formation channels have a characteristic χeff value is predicated on the assumption that χeff is a fixed quantity from BBH formation to merger and, ultimately, to detection. This thesis explores the possibility that BBHs in dense stellar systems such as globular clusters (GCs) can have their χeff altered through tidal disruption events (TDEs). Following a disruption, a portion of mass is ripped off of the star and becomes bound to either one or both of the BHs. This mass can be accreted onto the BHs and alter the magnitude and direction of the individual BH spins, effectively changing χeff. We use 3D Smoothed Particle Hydrodynamic (SPH) simulations to probe three unique BBH TDE scenarios. We find that the possibility to significantly alter the spin magnitudes and directions of LIGO BBHs (LBBHs) depends heavily on the mass ratio between the disrupted star and the disrupting BH. Furthermore, when TDEs lead to a significant change in spin we present a general model for how spins of LBBHs can be altered due to TDEs.
