5,282 research outputs found
Canonical Quantization of Spherically Symmetric Dust Collapse
Quantum gravity effects are likely to play a crucial role in determining the
outcome of gravitational collapse during its final stages. In this contribution
we will outline a canonical quantization of the LeMaitre-Tolman-Bondi models,
which describe the collapse of spherical, inhomogeneous, non-rotating dust.
Although there are many models of gravitational collapse, this particular class
of models stands out for its simplicity and the fact that both black holes and
naked singularity end states may be realized on the classical level, depending
on the initial conditions. We will obtain the appropriate Wheeler-DeWitt
equation and then solve it exactly, after regularization on a spatial lattice.
The solutions describe Hawking radiation and provide an elegant microcanonical
description of black hole entropy, but they raise other questions, most
importantly concerning the nature of gravity's fundamental degrees of freedom.Comment: 19 pages no figures. Contribution to a festschrift in honor of Joshua
N. Goldber
The Quantum Stress-Tensor in Self-Similar Spherical Dust Collapse
We calculate the quantum stress tensor for a massless scalar field in the 2-d
self-similar spherical dust collapse model which admits a naked singularity. We
find that the outgoing radiation flux diverges on the Cauchy horizon. This may
have two consequences. The resultant back reaction may prevent the naked
singularity from forming, thus preserving cosmic censorship through quantum
effects. The divergent flux may lead to an observable signature differentiating
naked singularities from black holes in astrophysical observations.Comment: Latex File, 19 page
Phase-Dependent Properties of Extrasolar Planet Atmospheres
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets. For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.Comment: 8 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Toward a Midisuperspace Quantization of LeMaitre-Tolman-Bondi Collapse Models
LeMa\^\i tre-Tolman-Bondi models of spherical dust collapse have been used
and continue to be used extensively to study various stellar collapse
scenarios. It is by now well-known that these models lead to the formation of
black holes and naked singularities from regular initial data. The final
outcome of the collapse, particularly in the event of naked singularity
formation, depends very heavily on quantum effects during the final stages.
These quantum effects cannot generally be treated semi-classically as quantum
fluctuations of the gravitational field are expected to dominate before the
final state is reached. We present a canonical reduction of LeMa\^\i
tre-Tolman-Bondi space-times describing the marginally bound collapse of
inhomogeneous dust, in which the physical radius, , the proper time of the
collapsing dust, , and the mass function, , are the canonical
coordinates, , and on the phase space. Dirac's
constraint quantization leads to a simple functional (Wheeler-DeWitt) equation.
The equation is solved and the solution can be employed to study some of the
effects of quantum gravity during gravitational collapse with different initial
conditions.Comment: 9 pages, 1 figure, Latex file. Minor corrections made. A general
solution of the constraints is presented. Revised version to appear in Phys.
Rev.
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