Gravitationally bouncing till the end: black stars

There are several proposals for regularizing the classical singularity of black holes that avoid information-loss problems. They present long-lived trapping horizons, with enormous inaccessible evaporation lifetimes. We propose an alternative regularization: The collapse of a stellar object would result in a series of damped bounces. In geometrical terms, each bounce amounts to the connection of a black-hole geometry with a white-hole geometry in a regular manner. Characteristics: i) the complete bouncing geometry is a solution of standard classical general relativity everywhere except in a transient region that necessarily extends beyond the gravitational radius; and ii) the duration of the bounce as seen by external observers is very brief. Transitions with long characteristic time scales are pathologically unstable, while geometries with short characteristic time scales are robust against perturbations, so that the corresponding processes could take place in real astrophysical scenarios. This motivates a search for new forms of stellar equilibrium such as dark stars: black ultra-compact horizonless objects, which could have a distinct observational imprint.