MG12 - Talk detail
 

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Abstract

Asymptotically FRW black holes.

Application of concepts like black hole and event horizon in cosmological context are not trivial, as has been shown in the last decade. We introduce special solutions of the LTB family representing collapsing over-dense regions extending to an expanding closed, open, or flat FRW model asymptotically. We study the dynamics of the collapsing region, and its density profile. The question of the strength of the central singularity and its nakedness, as well as the existence of an apparent horizon and an event horizon is dealt with in detail. Differences to the Schwarzschild black hole are addressed. Unlike models discussed so far in the literature, models we are suggesting represent mass condensation within the FRW universes leading to cosmological black holes without having usual pathologies known from other models: the cosmic fluid is dust and ideal producing a singularity at the center in the course of time. The central singularity is spacelike and not naked. In the case of flat or open universe models the singularity is weak and has distinct apparent and event horizons. The apparent horizons are not everywhere spacelike, to be compared with the Schwarzschild one which is null everywhere. This has already been noticed in a general context. While the apparent horizon is defined by the surfaces $R = 2M$, similar to the Schwarzschild horizon, the event horizon is further away. The toy models we have proposed show that one has to expect new effects while considering dynamical and cosmic black holes. The simple Schwarzschild static model may not reflect all the phenomena one may expect in observational cosmology.

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