Messy eaters: A diversity of supermassive black hole accretion behaviors revealed by nuclear transients

Abstract

Optical transient surveys have ushered in the golden era of time-domain astronomy and exposed an unexpected breadth of transient phenomena, including nuclear transients: flares powered by accretion onto supermassive black holes (SMBHs). These transients provide a means to identify otherwise-quiescent SMBHs. More importantly, if their physics is well understood, they can be used to study the properties of SMBHs across a range of masses and redshifts. Here I detail my work on the major classes of nuclear transients through both case studies of well-observed objects—all discovered by UH-affiliated surveys—and population studies to investigate trends. Chapters 2-5 discuss various aspects of tidal disruption events (TDEs), Chapter 6 explains coronal line emitters (CLEs) as TDEs in gas-rich environments, Chapters 7-9 establish the growing group of ambiguous nuclear transients (ANTs) with observables similar to both TDEs and active galactic nuclei, and Chapter 10 introduces the class of extreme nuclear transients (ENTs) which are the most energetic transients known. Each class is powered by accretion, but it is clear that the nuclear environment shapes their observational signatures. I finally conclude by summarizing our current understanding of nuclear transients and promising future directions to leverage their utility as probes of SMBHs.