Numerical Simulations of Super-Eddington Accretion Disks and Their Application to Tidal Disruption Events

Abstract

One of the major channels by which supermassive black holes (SMBHs) in the universe grow is through devouring stars in their host galaxy. The disruption of a star by a SMBH and subsequent disk formation appears as a bright transient known as a tidal disruption event (or TDE). Of significant interest in this work is the fact that the accretion disk during a TDE can exceed the Eddington rate. This thesis is dedicated to the study of the accretion disks, outflows, and emission associated with TDEs with the goal of understanding the dynamics which give rise to the emission we observe in TDEs. The gas dynamics are studied using numerical simulations which incorporate the effects of general relativity, magnetism, and radiation. I also make use of ray tracing to characterize the viewing angle dependent spectra. In Chapter 2, I simulate the disk formation process in a TDE to understand the disk properties early in the TDE. In Chapter 3, I also perform simulations which skip the disk formation to model the TDE assuming the accretion rate is super-Eddington and characterize the viewing angle dependent spectra and also find viable models for both jetted and non-jetted TDEs. In Chapter 4, I study an accretion flow which transitions from super-Eddington to sub-Eddington rates to understand the jet shutoff process in TDEs and find that a powerful magnetic field being present prevents the jet from shutting off. In Chapter 5, I study jets driven by radiation and characterize their radio/sub-millimeter emission and find that some TDEs may produce unseen emission due to the frequencies used in previous studies and this emission may lead to jets that can be detected by the next generation Event Horizon Telescope mission.