Conventional equations of state suggest that in complete gravitational collapse a singular state of matter with infinite density could be reached finally to a black hole, the characteristic feature of which is its apparent horizon, where light rays are first trapped. The loss of information to the outside world this implies gives rise to fatal difficulties with well-established principles of quantum mechanics and statistical physics.
The formation of a gravitational vacuum condensate star with a p=−ρ interior solves these problems and remarkably,
follows in fact from Schwarzschild’s second paper over a century ago. The surface tension of the condensate star surface
is the difference of equal and opposite surface gravities between the exterior and interior Schwarzschild solutions.
The First Law is a purely mechanical classical relation at zero temperature and zero entropy. The Schwarzschild time
of such a non-singular gravitational condensate star is a global time, fully consistent with unitary time evolution in quantum theory.
The advent of BH imaging by the EHT and Gravitational Wave Astronomy with LIGO should allow for observational tests of the
gravastar hypothesis, particularly in the discrete surface modes of oscillation and GW resonances or “echoes,” which may be
observable by advanced LIGO and successor GW detectors.
The effective field theory due to the conformal anomaly which gives rise to large vacuum polarization effects on
the would-be horizon of a ‘black hole’ and gravastar solutions in General Relativity will be discussed if time permits.