Abstract
In the last four decades, different programs have been carried out aiming at understanding the final fate of gravitational collapse of massive bodies once some prescriptions for the behaviour of gravity in the strong field regime are provided. The general picture arising from most of these scenarios is that the classical singularity at the end of collapse is replaced by a bounce. The most striking consequence of the bounce is that the black hole horizon may live for only a finite time. The possible implications for astrophysics are important since, if these models capture the essence of the collapse of a massive star, an observable signature of quantum gravity may be hiding in astrophysical phenomena. One intriguing idea that is implied by these models is the possible existence of exotic compact objects, of high density and finite size, that may not be covered by an horizon. The present article outlines the main features of these collapse models and some of the most relevant open problems. The aim is to provide a comprehensive (as much as possible) overview of the current status of the field from the point of view of astrophysics. As a little extra, a new toy model for collapse leading to the formation of a quasi static compact object is presented.
Highlights
Our present understanding of the universe and its evolution implies the existence of black holes, bodies whose masses are packed in such small volumes that not even light can escape
The general scenario presented above is extremely intriguing from an astrophysical point of view as it gets rid of space-time singularities while at the same time opening a possible observational window on quantum gravity phenomena
It is clear today that the black hole horizon is not a purely classical entity and it requires the addition of quantum physics to be properly understood
Summary
Our present understanding of the universe and its evolution implies the existence of black holes, bodies whose masses are packed in such small volumes that not even light can escape. Once a non trivial equation of state is introduced one would need to consider the fluid’s hydrodynamics and its thermodynamical properties In this case the boundary surface rb needs to be described by a surface layer that transports energy and momentum between the interior and the exterior, implying that the exterior can not be given by the Schwarzschild solution (typically a radiating Vaidya metric can be used [54]). In order to be physically valid such models would still need to describe well behaved matter sources (typically sources that satisfy energy conditions, have well behaved density profile and are non singular at the initial time) In this respect models with slow rotation have been considered in the past (see for example [66,67]). Most models dealing with quantum corrections to black hole formation deal with modifications of the above homogeneous models
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