What’s the Matter with Black Holes? Gravitational Condensate Stars & New Horizons in the LIGO Era

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 serious 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, actually follows 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 then recognized as 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.