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-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.Item Demographics and evolution of super massive black holes in quasars and galaxies(2008-08) Salviander, Sarah Triplett, 1971-; Shields, Gregory A.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.Item A numerical study of relativistic fluid collapse(2003) Noble, Scott Charles; Morrison, Philip J.; Choptuik, Matthew WilliamItem A numerical treatment of spin-1/2 fields coupled to gravity(2002-12) Ventrella, Jason Firmin, 1974-; Choptuik, Matthew William; Morrison, Philip J.Item Unification of QSOs via black hole and accretion properties(2004) Yuan, Michael Juntao; Wills, Beverley J.; Evans, Neal J.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.Item Unification of QSOs via black hole and accretion properties(2004-08) Yuan, Michael Juntao; Wills, Beverley J.; Evans, Neal J.