Simulating and Imaging Supermassive Black Hole Accretion Flows

Abstract

Supermassive black holes exist in the centers of nearly all galaxies. They are most frequently surrounded by hot, thick, and low-radiative-efficiency accretion flows, including in the Galactic Center radio source Sagittarius A* (Sgr A*) and at the base of the relativistic jet in the giant galaxy M87. In this thesis, I study these objects in two ways: with numerical simulations and with image reconstruction of data from the Event Horizon Telescope (EHT), a mm-wavelength Very Long Baseline Interferometry (VLBI) array. In the first part, I simulate both Sgr A* and M87 using two-temperature, radiative, general relativistic magnetohydrodynamics (GRMHD). Including radiation and thermodynamics in GRMHD simulations is necessary to predict the electron temperatures and emission from these objects, as electrons and ions in hot flows are far from mutual equilibrium. I also develop a method for moving beyond thermal equilibrium in simulations by evolving a full population of nonthermal electrons. In the second part, I describe a framework for imaging VLBI data with regularized maximum likelihood methods, and I detail its implementation in the eht-imaging software library. This framework allows VLBI data to be imaged with no a priori calibration, using only robust closure quantities. Finally, I present images from the first full EHT campaign on M87 reconstructed using eht-imaging and other methods. I conclude by describing measurements of the black hole shadow and mass from these first images of a supermassive black hole.