Paper (*cross-listing*): gr-qc/0508115
Date: Sun, 28 Aug 2005 15:44:25 GMT (149kb)

Title: Stable dark energy stars

Authors: Francisco S. N. Lobo

Comments: 10 pages, 6 figures, Revtex4
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The gravastar picture is an alternative model to the concept of a black hole,
where there is an effective phase transition at or near where the event horizon
is expected to form, and the interior is replaced by a de Sitter condensate. In
this work, a generalization of the gravastar picture is explored, by
considering a matching of an interior solution governed by the dark energy
equation of state, $\omega\equiv p/ \rho<-1/3$, to an exterior Schwarzschild
vacuum solution at a junction interface. The motivation for implementing this
generalization arises from the fact that recent observations have confirmed an
accelerated cosmic expansion, for which dark energy is a possible candidate.
Several relativistic dark energy stellar configurations are analyzed by
imposing specific choices for the mass function. The first case considered is
that of a constant energy density, and the second choice, that of a monotonic
decreasing energy density in the star's interior. The dynamical stability of
the transition layer of these dark energy stars to linearized spherically
symmetric radial perturbations about static equilibrium solutions is also
explored. It is found that large stability regions exist that are sufficiently
close to where the event horizon is expected to form, so that it would be
difficult to distinguish the exterior geometry of the dark energy stars,
analyzed in this work, from an astrophysical black hole.

\\ ( http://arXiv.org/abs/gr-qc/0508115 , 150kb)

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Paper (*cross-listing*): gr-qc/0508121
Date: Mon, 29 Aug 2005 20:04:22 GMT (17kb)

Title: Probing spacetime foam with extragalactic sources

Authors: W.A. Christiansen, Y. Jack Ng and H. van Dam (University of North
Carolina)
Comments: LaTeX, 9 pages, 1 figure
\\
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant galaxies. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.

\\ ( http://arXiv.org/abs/gr-qc/0508121 , 17kb)