Toward self-consistent models of high-energy transients from stellar remnants

Abstract

The universe is vast and mostly empty, but it is not static or dull. All massive stars collapse quickly, and some explode, releasing more energy in a few seconds than our own sun has over its entire lifetime. The cores of these stars form compact objects-- neutron stars and black holes-- that can spiral toward one another, emitting gravitational waves, ejecting mass, and producing light as they collide. Black holes swallow material by accreting from gaseous disks, sometimes launching relativistic, collimated outflows as they spin, tangling up the magnetic fields that are carried toward them. These luminous, fast events are responsible for making the heaviest elements in our universe and lighting up the sky as brief, bright sources that have captivated humans for over a millennium. Today, they are observable in huge numbers, not just with telescopes that are sensitive to light across the electromagnetic spectrum, from radio waves to gamma rays, but also with interferometers that detect gravitational waves. With upcoming observatories, we will soon be inundated with data in the field of time-domain astronomy, rendering the pursuit of complex, multi-physics models for stellar collapse, accretion, and mergers timely. In this dissertation, I study a range of high-energy astrophysical transients powered by massive stars and their remnants by numerically solving the equations that govern fluids in regions of strong gravity. I improve upon current state-of-the-art models that use idealized initial conditions or explore a limited region of parameter space to gain insight into the progenitor systems that drive luminous transients and their evolution. I begin by summarizing the observational and theoretical state of the field and providing an overview of the fundamental physical processes of relevance. I then present results from three studies I led, two of which deal with collapsing massive stars as progenitors for bursts of gamma-ray emission, and a third exploring magnetic fields with applications to stellar encounters with black holes. I conclude with a discussion of future work I intend to carry out, focusing on the synthesis of elements in these events, and preliminary results related to it.