Computer Science
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........6f&link_type=abstract
Thesis (PhD). UNIVERSITY OF NOTRE DAME, Source DAI-B 62/03, p. 1431, Sep 2001, 107 pages.
Computer Science
Scientific paper
In this work we investigate the dynamics of matter in the vicinity of compact objects such as black holes and neutron stars. While we review some observational results, we concentrate primarily on modeling these intense environments to explain observations and make predictions. We first reconstruct possible orbits for a collection of stars located within 0''.5 of Sagittarius A*, the putative supermassive black hole at the center of our Galaxy. These orbits are constrained by observed stellar positions and angular proper motions. The construction of such orbits serves as a baseline from which to search for possible deviations due to the unseen mass distribution in the central 1000 AU of the Galaxy. We also discuss the likelihood that some of these stars may eventually exhibit detectable relativistic effects. We then explore the implications of recently reported possible detections of very-high. We then explore the implications of recently reported possible detections of very-high-energy gamma-ray-induced showers in coincidence with observed gamma-ray bursts. We consider two mechanisms for generating this very-high-energy component - photo-pion production and proton-synchrotron radiation. We deduce likely values for the source luminosities in gamma-rays and hadrons based upon estimated red shifts for the possible detections. We find that the energy requirements are most easily satisfied if the energetic gamma-rays are produced predominantly via proton- synchrotron emission with a magnetic field near the equipartition limit in the burst environment. We lastly propose the Bardeen-Petterson effect as a mechanism for generating quasi-periodic brightness oscillations (QPOs) in the X-ray spectra of low-mass X- ray binaries with tilted accretion disks. The Bardeen- Petterson effect causes such a disk around a rapidly- rotating compact object to warp into the equatorial plane of the rotating body, resulting in an inner aligned accretion disk and an outer tilted accretion disk. We argue that the QPO frequency range predicted by this model is consistent with observed frequencies in both black-hole and neutron-star systems. We also describe the development and application of a numerical relativistic hydrodynamic study of this effect.
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