Speaker
Description
The classical black hole is one of the most extreme and scientifically rich products of classical
general relativity. However, it has predictions which still leave some uncomfortable; these primarily being
the nature of the event horizon and the mass singularity. This has led to the development of alternative
black hole ‘mimicking’ models which correct for these singularities and retain the observed properties of
black holes without requiring modifications to general relativity.
One of these mimickers is the ‘gravastar’; a dense spherical mass distribution constructed of a
cold gravitational condensate, colloquially called dark matter, inside a thin perfect-fluid shell. The density
of the gravastar varies and the sizes for which it exhibits black hole properties are unknown. It has also
been shown that such a stellar configuration can exist in thermodynamic equilibrium while correcting the
information paradox. However, to replace the classical black hole as the end-product of gravitational
collapse, as is currently accepted, an analysis of its dynamical stability is required. By perturbing the shell
from gravitational equilibrium – as also occurs during mass accretion, binary coalescence, and other black
hole events – its dynamical stability can be discussed. If such a body could reach harmonic behaviour
around equilibrium without collapsing to a classical black hole, or alternatively leading to stellar explosion,
then it would suitably describe black hole behaviour while correcting for their singularities.
In this work we sought exactly this. By thoroughly investigating the equations of motion of the
thin shell, we determined the mass sequences for which a stable gravastar can exist as well as their
dynamical stability to a first order perturbation theory. We found that although such a configuration does
indeed have black hole mimicking equilibrium forms, they are dynamically unstable and thus not expected
to exist in nature.
