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Thesis (M.Sc.). / Written for the Dept. of Mathematics and Statistics. Title from title page of PDF (viewed 2008/01/15). Includes bibliographical references.

The extension of the concepts of Newtonian cosmology to a universe consisting of a hierarchy of metagalaxies is fairly straightforward. However, in general relativistic cosmology, the construction of such a hierarchical universe is a difficult problem. It is the purpose of this work to examine some aspects of hierarchical cosmology in both the Newtonian and general relativistic cases. It is suggested that the metagalaxy may be a black hole or Schwarzschild object,(to account for the fact that no objects which could be identified as metagalaxies have been, as yet, observed. Some features of this concept are discussed. Tidal forces exerted on a metagalaxy, due to others distributed around it, are estimated in the Newtonian case. Such tidal forces may or may not be detectable, depending on the distance between metagalaxies. The interior of a metagalaxy is represented by a Fried-mann model, with given values of k and A. The Friedmann model is matched at the boundary to a Schwarzschild spacetime. The consequences of this and related calculations suggest that in most cases, a metagalaxy may be a black hole for only part of its lifetime, i.e., for other times, it may be optically detectable to an exterior observer. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

We investigate the possibility that present-day galaxies and their dark matter halos contain a population of massive black holes (MBHs) that form by hierarchical merging of the black hole remnants of the first stars in the Universe. Some of the MBHs may be large enough or close enough to the centre of the galactic host that they merge within a Hubble time. We estimate to what extent this process could contribute to the mass of the super-massive black holes (SMBHs) observed in galactic centres today. The relation between SMBH and galactic bulge mass in our model displays the same slope as that found in observations. Many MBHs will not reach the centre of the host halo, however, but continue to orbit within it. In doing so MBHs may remain associated with remnants of the satellite halo systems of which they were previously a part. Using a semi-analytical approach that explicitly accounts for dynamical friction, tidal disruption and encounters with galactic disks, we follow the hierarchical merging of MBH systems and their subsequent dynamical evolution inside the respective host halos. In this context two types of dynamical processes are examined in more detail. We predict the mass and abundance of MBHs in present-day galactic halos and also estimate the MBH mass accretion rates considering two different accretion scenarios. On this basis we determine the bolometric, optical and X-ray luminosity functions for the accreting MBHs using thin disk and advection dominated accretion flow models. Our predicted MBH X-ray emissions are then compared with observations of ultra-luminous X-ray sources in galaxies. We find that the slope and normalisation of the predicted X-ray luminosity function are consistent with the observations. We also estimate the rate of gravitational wave events received from MBH mergers across all redshifts. At the end of their lives the first stars may explode in supernovae that are associated with gamma ray bursts (GRBs). Provided these are in principle detectable we have estimated the expected rate of events observed.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, June 2016. / This dissertation will focus on spin-3/2 perturbations on N-dimensional Schwarzschild black holes, with the aim of calculating the numerical values for the quasi-normal modes (QNMs) and absorption probabilities associated with these perturbations. We begin by determining the spinor-vector eigenmodes of our particles on an (N-2)-dimensional spherical background. This allows us to separate out the angular part and radial part on our N-dimensional Schwarzschild metric. We then determine the equations of motion and e ective potential of our particles near the N-dimensional black hole. Using techniques such as the Wentzel-Kramers-Brillouin and Improved Asymptotic Iterative Method we determine our QNMs and absorption probabilities. We see that higher dimensional black holes emit QNMs with larger real and imaginary values, this would imply they emit higher energy particles but that these particles are highly dampened and therefore would be di cult to detect. The results of the QNMs make sense if we also consider the e ective potential surrounding our black holes with the potential function increasing with increasing number of dimensions.

Supermassive black hole binaries (SMBHBs) are the natural consequence of galaxy mergers and should form frequently in galactic nuclei. Especially at sub-parsec separations, where the binary evolution is slow, SMBHBs should be fairly abundant. However, the observational evidence remains elusive. In this thesis, we focus on periodic variability of quasars as a potential signature of compact SMBHBs. First, we present a systematic search for periodic variability in the photometric database of the Palomar Transient Factory. Our search in a large sample of ~35,000 quasars returned 50 candidates, 33 of which remain significant after the reanalysis of extended light curves including data from the Catalina Real-Time Transient Survey and the intermediate PTF. Our candidates have periods of a few hundred days. Next, we focus on independent signatures that could verify the binary nature of the candidates. We present a case study of quasar PKS 1302-102, the first candidate that emerged from the large time-domain surveys. We search for multiple periodic components in the variability with a characteristic frequency pattern predicted by hydrodynamical simulations of circumbinary disks. We do not find compelling evidence for a secondary period. Additionally, in compact SMBHBs, relativistic Doppler boost should be significant and may dominate the variability. This model was suggested as a smoking-gun signature for quasar PKS 1302-102, since it is not expected in quasars with a single BH and it offers a robust prediction, which can be tested with multi-wavelength data. With a control sample of non-periodic quasars, we test whether this signature is distinct from the intrinsic multi-wavelength variability of quasars. We concluded that the Doppler boost does not provide a sharp test for SMBHBs.

Thesis (Ph. D.)--Open University. BLDSC no. DXN041011.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 110-116). Available also in a digital version from Dissertation Abstracts.

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. / text

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