Faraoni, Valerio, Vitagliano, Vincenzo, Sotiriou, Thomas P. and Liberati, Stefano (2012), "Dynamical apparent horizons in inhomogeneous Brans-Dicke universes", PHYSICAL REVIEW D, 86, 6.
Abstract: The presence and evolution of apparent horizons in a two-parameter
family of spherically symmetric, time-dependent solutions of Brans-Dicke
gravity are analyzed. These solutions were introduced to model space-
and time-varying gravitational couplings and are supposed to represent
central objects embedded in a spatially flat universe. We find that the
solutions possess multiple evolving apparent horizons, both black hole
horizons covering a central singularity and cosmological ones. It is not
uncommon for two of these horizons to merge, leaving behind a naked
singularity covered only by a cosmological horizon. Two characteristic
limits are also explicitly worked out: the limit where the theory
reduces to general relativity and the limit where the solutions become
static. The physical relevance of this family of solutions is discussed.
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