<p> Accretion on to black holes powers some of the most luminous objects in the universe. In this thesis I present a series of works aimed at constraining the properties of black hole accretion in a variety of astrophysical systems. Numerical methods are vital for studying the multi-scale and non-linear physics of these systems. First I introduce <tt>DiscoGR,</tt> the first implementation of numerical general relativistic magnetohydrodynamics on a moving mesh. <tt> DiscoGR</tt> is capable of efficiently and accurately simulating highly supersonic thin accretion disks, the objects responsible for many luminous accretion events. I apply <tt>DiscoGR</tt> to study minidisks: accretion disks around a single member of a binary black hole system. Spiral shock waves, excited by tidal forces from the binary companion, propagate throughout the disk, causing efficient accretion by purely hydrodynamical means. The shock-driven accretion has an effective alpha parameter of the order 0.01, comparable with accretion driven by the magnetorotational instability. Furthermore, shocks near the black hole contribute to a radiative signature brighter in the hard x-rays than the standard Novikov-Thorne model. Finally I present an analysis of gamma-ray burst (GRB) x-ray afterglow light curves. The analysis fits the data from the <i>Swift-XRT</i> directly to a suite of hydrodynamical simulations, constraining the jet opening angle and, for the first time, the viewing angle of these events. I find typically the viewing angle to be 0.57 of the jet opening angle. Observing a GRB off-axis can reduce the inferred energy of the central engine, thought to be a neutron star or accreting black hole, by up to a factor of four.</p><p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10261761 |
| Date | 22 November 2017 |
| Creators | Ryan, Geoffrey |
| Publisher | New York University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
Page generated in 0.002 seconds