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Abstract
The ability of black holes to gravitationally absorb massless particles, e.g. photons, is a defining attribute of the system. This thesis addresses the question of whether or not such absorption properties may arise in a system lacking other defining features of the black hole, e.g. a singularity in the metric and an event horizon. An example of such a system is a very dense, spherically symmetric static body of radius R which slightly exceeds its Schwarzschild radius r_s. We consider quantum particles in the gravitational field of this ``near-black-hole" object.
In the continuum (scattering case) we find a new spectrum of resonances: long lived metastable states which correspond to an incident particle spending long periods trapped on the interior of the body. In the black hole limit (R\to r_s) the resonance lifetimes become arbitrarily long and any test particle sent by an external observer will appear to have been lost forever: a purely elastic scattering event gives rise to absorption. Furthermore, calculation of the low energy absorption cross section for capture to these resonances, in the black hole limit, exactly matches that of the pure black hole system. Thus bodies that are not black holes may develop black hole-like absorption properties. Additionally we consider the case of a central body modelled as a perfect fluid sphere of constant density. This system develops a pressure singularity well before R=r_s, and so the black hole limit is out of reach. Nevertheless, there still exists a dense spectrum of long lived resonances which may capture massless particles.
In the case of bound particles by the potential of a near-black-hole object we find that as R\to r_s the spectrum collapses and becomes quasi-continuous (\delta \epsilon \to 0). Furthermore, prior to the black hole limit there are no zero or negative energy bound states, forbidding particle pair production and subsequent effects from occurring.