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Dissertation/Thesis Abstract

Numerical Simulations of Black Hole Accretion
by Ryan, Geoffrey, Ph.D., New York University, 2017, 182; 10261761
Abstract (Summary)

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 DiscoGR, the first implementation of numerical general relativistic magnetohydrodynamics on a moving mesh. DiscoGR is capable of efficiently and accurately simulating highly supersonic thin accretion disks, the objects responsible for many luminous accretion events. I apply DiscoGR 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 Swift-XRT 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.

Indexing (document details)
Advisor: MacFadyen, Andrew
Commitee: Grosberg, Alexander, Gruzinov, Andrei, Hogg, David, Modjaz, Maryam
School: New York University
Department: Physics
School Location: United States -- New York
Source: DAI-B 79/02(E), Dissertation Abstracts International
Subjects: Astrophysics
Keywords: Accretion disks, Black holes, Fluid dynamics, General relativity, Magnetohydrodynamics, Numerical methods
Publication Number: 10261761
ISBN: 978-0-355-40689-4
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