Abstract
Classic black hole mechanics and thermodynamics are formulated for stationary black holes with event horizons. Alternative theories of gravity of interest for cosmology contain a built-in time-dependent cosmological “constant” and black holes are not stationary. Realistic black holes are anyway dynamical because they interact with astrophysical environments or, at a more fundamental level, because of backreaction by Hawking radiation. In these situations, the teleological concept of event horizon fails and apparent or trapping horizons are used instead. Even as toy models, black holes embedded in cosmological “backgrounds” and other inhomogeneous universes constitute an interesting class of solutions of various theories of gravity. We discuss the known phenomenology of apparent and trapping horizons in these geometries, focusing on spherically symmetric inhomogeneous universes.
Highlights
Black holes are a fundamental prediction of General Relativity (GR) and have been the subject of a celebrated theory of dynamics and thermodynamics developed in the 1970s [1]
A cosmological background: real black holes are embedded in the universe and, this feature may be irrelevant for their astrophysics, their asymptotics are quite relevant in problems of principle and in mathematical physics
To conclude this brief excursion on the subject of dynamical cosmological black holes and their relations with modified gravity, one should first realize that, while it is auspicable to find new inhomogeneous solutions amenable to this physical interpretation, it is usually harder to find whether apparent horizons exist, and to determine their location, nature, and dynamical behaviour, and some effort should be devoted to these goals
Summary
Black holes are a fundamental prediction of General Relativity (GR) and have been the subject of a celebrated theory of dynamics and thermodynamics developed in the 1970s [1]. The black holes considered in these studies are stationary solutions of GR. Real black holes are non-stationary due to several possible processes:. A cosmological background: real black holes are embedded in the universe and, this feature may be irrelevant for their astrophysics, their asymptotics are quite relevant in problems of principle and in mathematical physics. Hawking radiation and evaporation affect all black holes and are, important and unavoidable in all problems of principle. They become important for hypothetical small black holes in their final stages or perhaps even for primordial black holes in the early universe
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