Plasma Effects in Black Hole Accretion

Abstract

Supermassive black holes exert powerful influences on nearby stars, entire galaxies, and even the intergalactic medium, despite having event horizons that are smaller than the Solar System. Recent observations by the Event Horizon Telescope revealed asymmetric ring-like structures around M87* and Sgr A*, produced by a relativistic plasma consisting of ions, electrons, and possibly positrons. The characteristics of this extremely energetic plasma on microscopic scales fundamentally shape the system's large-scale dynamics. With such unprecedentedly detailed images, we require better models of the accretion flow. I have developed and applied first-principles models of relativistic plasmas around black holes, necessary for interpreting and predicting the results of observations across the electromagnetic spectrum. Microscopic plasma effects not only affect the overall state of accretion but also alter the way we observe these systems by changing the distribution function of synchrotron-emitting electrons. Hot accretion flows, which are believed to operate around low-luminosity galactic nuclei, are the focus of this work. Such systems are often associated with strong outflows, winds, and jets. Nevertheless, the closest low-luminosity supermassive black hole, Sagittarius A*, located in the center of our galaxy, appears to lack a powerful jet. A simplified model of spherical accretion demonstrates why such systems might be unable to produce strong jets.