# Browsing by Subject "Black holes (Astronomy)"

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Item Computational and astrophysical studies of black hole spacetimes(2004) Bonning, Erin Wells; Matzner, Richard A. (Richard Alfred), 1942-Show more This dissertation addresses three problems of interest concerning astrophysical black holes, namely the numerical solution of Einstein’s equations for a spacetime containing two orbiting and coalescing black holes, the simulation of a light curve from an accretion disk near the innermost orbit around a spinning black hole, and determining relations between central black hole mass and host galaxy properties in active galactic nuclei. I first address the problem of setting the initial conditions for the Cauchy formulation of general relativity. I present the solution of the constraint equations via a conformal decomposition and discuss the construction of the background fields as superposed Kerr-Schild black holes. The constraint equations are solved for two black holes with arbitrary linear and angular momenta. The binding energy and spin-spin coupling of the two holes are computed in the initial data slice and analyzed. I discuss the extent to which the superposed Kerr-Schild initial data limits extraneous radiation and estimate the accuracy of determinations of the innermost stable circular orbit through sequences of initial data. The second topic concerns the time variability of isotropically radiating material orbiting in an idealized accretion disk around a spinning black hole. I solve the geodesic equations for photon propagation from the surface of the disk to an observer for different orbital parameters. The general relativistic effects upon the signal received are calculated, including the energy shift, relativistic time delay, and gravitational lensing. I produce light curves showing the change in flux over time due to the relativistic effects. Applications of this model to stellar-mass systems as well as super-massive black holes are discussed. Lastly, I discuss the relationship between a galaxy’s central black hole and its evolutionary history. In particular I examine the correlations among host galaxy luminosity, stellar velocity dispersion, and central black hole mass in active galactic nuclei. I derive black hole masses and stellar velocity dispersions from quasar broad and narrow emission lines, respectively. The utility of using the narrow line emitting gas as a surrogate for stellar velocity dispersion is investigated through examining host magnitudes and narrow [O III] line widths for low redshift quasars.Show more Item Demographics and evolution of super massive black holes in quasars and galaxies(2008-08) Salviander, Sarah Triplett, 1971-; Shields, Gregory A.Show more This dissertation addresses the co-evolutionary relationship between central super-massive black holes and host galaxies. This relationship is suggested by observed correlations between black hole mass (M[subscript BH]) and properties of the host galaxy bulge. We first discuss investigation of the relationship between MBH and host galaxy velocity dispersion, [sigma subscript asterisk], for quasars in the Sloan Digital Sky Survey (SDSS). We derive MBH from the broad emission line width and continuum luminosity, and [sigma subscript asterisk] from the width of narrow forbidden emission lines. For redshifts z < 0.5, our results agree with the locally-observed M[subscript BH]- [sigma subscript asterisk] relationship. For 0.5 < z < 1.2, the M[subscript BH]- [sigma subscript asterisk] relationship appears to evolve with redshift in the sense that bulges are too small for their black holes. Part of this apparent trend can be attributed to observational biases, including a Malmquist bias involving the quasar luminosity. Accounting for these biases, we find approximately a factor of two evolution in the M[subscript BH]- [sigma subscript asterisk] relationship between the present and redshift z [approximately equal] 1. The second topic involves a search for the largest velocity dispersion galaxies in the SDSS. Black holes in quasars can have M[subscript BH]exceeding 5 billion M[mass compared to the sun], implying [sigma subscript asterisk] > 500 km s−1 by the local M[subscript BH]- [sigma subscript asterisk] relationship. We present high signal-to-noise HET observations for eight galaxies at redshift z < 0.3 from the SDSS showing large [sigma subscript asterisk] while appearing to be single galaxies in HST images. The maximum velocity dispersion we find is [sigma subscript asterisk] = 444 km s−1, suggesting either that quasar black hole masses are overestimated or that the black hole - bulge relationship changes at high black hole mass. The third topic involves work contributed to co-authored papers, including: (1) evidence for recoiling black holes in SDSS quasars, (2) the [sigma][O III] - [sigma subscript asterisk] relationship in active galactic nuclei (AGN), and (3) accretion disk temperatures and continuum colors in quasars. Lastly, we discuss research in progress, including: (1) possible physical influences on the width of narrow emission lines of SDSS AGN, including the gravitational effect of the black hole, and (2) a search for binary AGN in the SDSS using double-peaked [O III] emission lines.Show more Item A numerical study of relativistic fluid collapse(2003) Noble, Scott Charles; Morrison, Philip J.; Choptuik, Matthew WilliamShow more We investigate the dynamics of self-gravitating, spherically-symmetric distributions of fluid through numerical means. In particular, systems involving neutron star models driven far from equilibrium in the strong-field regime of general relativity are studied. Hydrostatic solutions of Einstein’s equations using a stiff, polytropic equation of state are used for the stellar models. Even though the assumption of spherical symmetry simplifies Einstein’s equations a great deal, the hydrodynamic equations of motion coupled to the time-dependent geometry still represent a set of highly-coupled, nonlinear partial differential equations that can only be solved with computational methods. Further, many of the scenarios we examine involve highly-relativistic flows that require improvements upon previously published methods to simulate. Most importantly, with techniques such as those used and developed in this thesis, there is still considerable physics to be extracted from simulations of perfect fluid collapse, even in spherical symmetry. Here our particular focus is on the physical behavior of the coupled fluid-gravitational system at the threshold of black hole formation—so-called black hole critical phenomena. To investigate such phenomena starting from conditions representing stable stars, we must drive the star far from its initial stable configuration. We use one of two different mechanisms to do this: setting the initial velocity profile of the star to be in-going, or collapsing a shell of massless scalar field onto the star. Both of these approaches give rise to a large range of dynamical scenarios that the star may follow. These scenarios have been extensively surveyed by using different initial star solutions, and by varying either the magnitude of the velocity profile or the amplitude of the scalar field pulse. In addition to illuminating the critical phenomena associated with the fluid collapse, the resulting phase diagram of possible outcomes provides an approximate picture of the stability of neutron stars to large, external perturbations that may occur in nature. Black hole threshold, or critical, solutions, occur in in two varieties: Type I and Type II. Generically, a Type I solution is either static or periodic and exhibits a finite black hole mass at threshold, whereas a Type II solution is generally either discretely or continuously self-similar and characterized by infinitesimal black hole mass at threshold. We find both types of critical behavior in our space of star solutions. The Type I critical solutions we find are perturbed equilibrium solutions with masses slightly larger than their progenitors. In contrast, the Type II solutions are continuously self-similar solutions that strongly resemble those found previously in ultra-relativistic perfect fluids. The boundary between these two types of critical solutions is also discussed.Show more Item A numerical treatment of spin-1/2 fields coupled to gravity(2002-12) Ventrella, Jason Firmin, 1974-; Choptuik, Matthew William; Morrison, Philip J.Show more Item Radiative problems in black hole spacetimes(1995-12) Marsa, Robert Lee; Not availableShow more Item Unification of QSOs via black hole and accretion properties(2004-08) Yuan, Michael Juntao; Wills, Beverley J.; Evans, Neal J.Show more Although the orientation-based AGN unification scheme can successfully explain many QSO observational phenomena, orientation does not address all the object-to-object differences in QSOs. Physical differences of the underlying engine, such as luminosity, black hole mass (MBH) and Eddington ratio (L/LEdd), are crucial to our understanding of QSO central engines. Broad Absorption Line (BAL) QSOs are a particularly interesting type of QSO that exhibits both orientation and intrinsic property-related observational features. In this thesis, I studied a large QSO sample, including 16 BAL QSOs at z ∼ 2, with new spectroscopy data for the Hβ region. This sample covers a luminosity range substantially wider than similar studies in the past and hence enables us to differentiate luminosity from other underlying mechanisms driving QSO observational properties. I found that overall, QSOs accrete at close to Eddington rate. Due to the narrow range of L/LEdd, the QSO luminosity is almost directly proportional to the MBH. The slight increase of L/LEdd at high luminosity suggests that the QSO MBH distribution has a high mass cut-off near 109M¯. Compared with radio quiet QSOs, radio loud QSOs tend to have higher MBH for the same luminosity. The [O iii] versus Fe ii anti-correlation discovered from low luminosity QSOs (BGEV1) extends to high luminosity objects with BAL QSOs at the weak [O iii] strong Fe ii end of the trend, and radio loud QSOs at strong [O iii] weak Fe ii end of the trend. Both [O iii] and Fe ii strengths are well correlated with L/LEdd over the entire luminosity range, indicating that L/LEdd is the physical driver behind the BGEV1 correlations. Although BAL QSOs have higher L/LEdd than most QSOs, they do not stand out when compared with high luminosity non-BAL QSOs. One interpretation is that [O iii] and Fe ii are indirectly linked to L/LEdd via the availability of accretion fuel. Even with the expanded luminosity coverage, I could not confirm the existence of an Hβ Baldwin Effect. An [O iii] ”Baldwin Effect” is observed, suggesting a limited amount of [O iii] NLR gas in all QSO systems.Show more