Master of Science / General Relativity (GR) is founded on the revolutionary idea that space and time are merely parts of a greater, unified whole: spacetime. Furthermore, the force we know as gravity results from the bending and stretching of the geometry of spacetime by its energetic contents. GR is notorious for its mathematical complexity and subtlety, meaning that an intuitive understanding of a spacetime is difficult. One of the best approaches to studying the properties of a given spacetime is to consider its geodesic structure—that is, to consider the motion of unaccelerated, “free-falling” particles. This report presents the results of such a study into two important spacetimes — the Kerr solution for a rotating black hole, and the Robertson-Walker solution for a homogeneous universe.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Binary black hole mergers are the strongest expected producers of graviational radiation in the universe. Ground-based and proposed space-based gravitational wave detectors will benefit from simulations modeling the mergers and extracting the resulting gravitational waveforms. Producing templates of waveforms will both aid the likelihood of detection and the estimation of parameters (mass ratio, spin, etc.). openGR is modular, open framework development to carry out simulations of binary black hole mergers. While designed with the two-body problem in mind, openGR will evolve most general spacetimes. This work overviews the capabilities of openGR and the corresponding physics involved. openGR supports both excision and puncture methods. When excising the black hole, to date we have used only the weakly hyperbolic ADM formulation of the Einstein’s equations. As expected from a weakly hyperbolic system, instabilites arise and crash the code when simulating even just a single boosted black hole in Kerr-Schild coordinates. In contrast, successful mergers of two black holes have been achieved using the puncture method. We demonstrate such a simulation in Ch 8. In this case, we make use of a BSSN formulation of Einstein’s equations (a strongly hyperbolic system). / text

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Master of Science / General Relativity (GR) is founded on the revolutionary idea that space and time are merely parts of a greater, unified whole: spacetime. Furthermore, the force we know as gravity results from the bending and stretching of the geometry of spacetime by its energetic contents. GR is notorious for its mathematical complexity and subtlety, meaning that an intuitive understanding of a spacetime is difficult. One of the best approaches to studying the properties of a given spacetime is to consider its geodesic structure—that is, to consider the motion of unaccelerated, “free-falling” particles. This report presents the results of such a study into two important spacetimes — the Kerr solution for a rotating black hole, and the Robertson-Walker solution for a homogeneous universe.

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

First observed as early as redshift z = 7 and now thought to be found at the centre of every massive galaxy in the local Universe, the evolution history of supermassive black holes (SMBHs) spans over 13 billion years. In this thesis, the coevolution between SMBHs and their host galaxies is studied using a set of hydrodynamical simulations to isolate different components of the interaction between black holes and cosmic gas. The simulations range from black hole accretion in an idealised context to the impact of feedback in the cosmological simulations of the HORIZON suite. The origin of SMBHs during the first billion years of the Universe is a highly non-linear problem, where small-scale behaviour influences large- scale behaviour and vice versa. Gas fuelling a black hole flows from the cosmic web, through its host galaxy and into the black hole's gravitational potential, before eventually reaching its event horizon. Even discounting the complex physical processes at play, resolving the 19 orders of magni- tude in spatial scale involved is beyond the capabilities of current simula- tions. Some of the length scales therefore have to be covered by sub-grid algorithms which need to be able to handle a wide range of environments. Idealised accretion simulations presented in this thesis show that the Bondi-Hoyle-Lyttleton (BHL) accretion algorithm is sufficiently versatile. It automatically determines the accretion rate onto the black hole by the mass flux into its accretion region when the black hole's gravitational po- tential becomes resolved. The accretion rate onto the black hole therefore naturally converges to the correct solution once the size of the accretion region approaches the physical size of the black hole. A drag force algo- rithm that compensates for unresolved dynamical friction, on the other hand, produces a force on the black hole that can unphysically accelerate it relative to the bulk flow of the gas. It needs to be switched off when gas properties are measured within the black hole's gravitational potential. A study of black hole accretion within an isolated cooling halo confirms that the accretion algorithm is able to handle the flow configurations en- countered within an evolving galaxy. To ensure gas is always accreted within the black hole's gravitational potential, a refinement algorithm called "zoom-within-zoom" is introduced in this thesis. It allows the black hole environment to be resolved by orders of magnitude above that of its host galaxy. A low mass seed black hole with a strong drag force early on takes advantage of this extra information during the black hole's early evolution. In the longer term, resolving gas clouds in the black hole vicin- ity to sub-pc scales has a lasting impact on both the mass evolution and duty cycle of massive black holes. Sub-pc size clumps also play a deciding role in the first 200 Myr of evo- lution of a SMBH progenitor in a full cosmological context: 90% of its mass is gained through interactions with dense clumps, which fuel super- Eddington accretion bursts. Once the gas within the host galaxy settles into a rotationally supported disc, star formation and black hole accre- tion slow down. As both primarily occur within the central 30 pc of the compact host galaxy, star formation in proto-galaxies has a major impact on black hole accretion even in the absence of feedback. At low redshift, on the other hand, feedback becomes the crucial link between a SMBH and its host galaxy. A comparison of two simulations from the HORIZON suite, run with and without active galactic nuclei (AGN) feedback respectively, shows that AGN feedback is able to prevent as much as 90% of the stellar mass from forming in the most massive galaxies. Quenching proceeds via a combination of AGN driven outflows and reduced inflows and evolves with redshift as the M_SMBH - M_* relation flattens from z = 5 to z = 0. In conclusion, neither the evolution of galaxies nor that of black holes can be understood without the context of the other. At high redshift, the competition between star formation and black hole accretion inside the compact host galaxy intrinsically links the origin of SMBHs to the early evolution of galaxies. At low redshift, AGN feedback modulates the gas supply of the host galaxy, which has a lasting impact on star formation. The coevolution of black holes and galaxies therefore spans their entire history.

The Bahamas are thousands of islands stretching along the coast of Florida and south to the tropic of cancer. An aerialv iew, spectaculaar s it is, shows only a small part of the islands, a larger part is submerged and discernible only by the abundance of blue dots onshorea nd in the shallow water around the islands. The blue holes are entrancesto an underwater world wherein biology seems to have slowed down to offer a fascinating view of species rarely seen elsewhere, and of rock formations that tell a story of the subterranianw orld below the islands. My studies were inspired by curiosity and the desire to make a contribution to the preservationo f this unique and irreplaceablew indow into the pastf or geologistsa nd biologists alike. Important questions as to how the caves formed and when and what the role of cavel ife might havep layed in the excavationp rocessesa re addressedin this thesis. As a result of these studies bacteria must be considered as possibly active participantsi n the formation processesa fter the time when the rising watertablef looded all the Bahamian caves. The layering, often in hypersharp zones of biological material, matches or is perhaps caused by, equally dramatic changes in hydrogen ions and acetate and sulphate concentrations. In both caves, pH profiles were observed that varied sharply over very short distances. In all three study sites it could be shown that, vertically and horizontally, the geochemical perimeters varied dramatically. Organically mediated processes are a dominant control on dissolution within the fresh, mixing, and saline zone. The combined generationof C02 results, known from earlier studies, and 112S and other bacterially measured activity, supports this finding. Retention of suspended organic matter was directly proportional to the salinity gradient. Elevated levels of DOC, POM, and acetate at the two major density interfaces confirm this finding. In the results, generated from CHN&S methods, wall rock material was found to contain residual carbon for potential microbial use, and large bacterial populations were identified through the SEM method in excess of what was measured within the water column. Significant lepidocrocite deposits (dimorphose iron oxihydroxide) were identified as a fraction of the cave sediment, and material known as "mung7, based on amino-acid analysis, was shown to be proteinaceous. This mung appears to be unique to caves in the Bahamas. In a sense the cave system is an underground geo-biosphere wherein the peculiar water flow patterns foster a specific, sometimes rich and unusual, fauna and flora that is a treasure for science and a sight for humans to enjoy.

This thesis is a study of the theory and phenomenology of trans-Planckian black holes, in TeV gravity extra-dimensional theories. The introduction starts with the motivation for this beyond the Standard Model scenario (chapter 1), a summary of the theoretical tools to formulate the theory, and a summary of the best bounds from experiment (chapter 2). In chapter 3, after setting up some notation and describing well known solutions in 4 + n-dimensional general relativity, we construct an approximate effective background for a brane charged rotating higher-dimensional black hole. This is achieved by solving Maxwell's equations perturbatively on the brane to obtain the electromagnetic field. A brief study of the effect of rotation on the absorption of classical particles is also provided. Chapter 4 is a review of methods to model black hole production focusing on the trapped surface method. A model for the mass and angular momentum loss into gravitational radiation is described. A detailed study of the effects of particle mass and charge, for fermions and scalars on the effective brane charged background, is presented in chapters 5 and 6. After coupling the fields to the background, the separated radial wave equations for both perturbations are obtained (chapter 5) and they are integrated using a detailed numerical method as well as analytic approximations (chapter 6). Similarly, a method is described to obtain high accuracy angular functions based on series expansions. We conclude the theoretical study by evaluating the Hawking spectra for various combinations of spin, mass, charge and rotation parameters, and discuss them comparatively. The last part of the thesis is on the implementation of the theoretical results in the new CHARYBDIS2 Monte Carlo simulation of black hole production and decay (chapter 7), and on the analysis of the phenomenological consequences (chapter 8). The main new features implemented in CHARYBDIS2 are: a full treatment of the spin-down phase using the angular and energy distributions of the associated Hawking radiation; an improved model for energy and angular momentum loss in the production process, and a wider range of options for the Planck-scale termination of the decay. The main conclusions of this thesis and an outlook on future directions are summarised in the final chapter.

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