Related papers: Black hole event horizons are cosmologically coupl…
This paper considers the nature of apparent horizons for astrophysical black hole situated in a realistic cosmological context. Using semi-tetrad covariant methods we study the local evolutions of the boundaries of the trapped region in the…
In four dimensions the topology of the event horizon of an asymptotically flat stationary black hole is uniquely determined to be the two-sphere $S^2$. We consider the topology of event horizons in higher dimensions. First, we reconsider…
Several recently found properties of the event horizon of black holes are discussed. One of them is the reflection of the incoming particles on the horizon. A particle approaching the black hole can bounce on the horizon back, into the…
Binary black holes occupy a special place in our quest for understanding the evolution of galaxies along cosmic history. If massive black holes grow at the center of (pre-)galactic structures that experience a sequence of merger episodes,…
How to describe a black hole embedded in an expanding universe is an important topic. Some models about this issue are suggested by assuming that the metric is a conformal transformation of the Schwarzschild metric or of the isotropic black…
Constraints on the geometries of static spherically symmetric black holes are obtained by requiring that the spacetime curvature be analytic at the event horizon. Further constraints are obtained by requiring that the semiclassical trace…
We consider spherically-symmetric black holes in semiclassical gravity. For a collapsing radiating thin shell we derive a sufficient condition on the exterior geometry that ensures that a black hole is not formed. This is also a sufficient…
The growth of black holes and the formation and evolution of galaxies appear to be linked at such a fundamental level that we think of the two as `co-evolving.' Recent observations show that this co-evolution may be complex and the result…
We construct and investigate the dynamical black hole spacetime embedded in the expanding universe filled with cosmic fluid, such as dark energy. When the equation of state (EoS) parameter of the fluid is a constant, we find exact solutions…
I review elements of the foundations of black-hole theory with attention to problematic issues, and describe some techniques which either seem to help with the difficulties or at least investigate their scope. The definition of black holes…
Kerr-Schild solutions of the Einstein-Maxwell field equations, containing semi-infinite axial singular lines, are investigated. It is shown that axial singularities break up the black hole, forming holes in the horizon. As a result, a…
In accordance with current models of the accelerating Universe as a spacetime with a positive cosmological constant, new results about a cosmological upper bound for the area of stable marginally outer trapped surfaces are found taking into…
We explore the possibility that spacetime horizons in 4D general relativity can be treated as manifestations of higher dimensions that induce fields on our 4D spacetime. In this paper we discuss the black hole event horizon, as an example…
While extreme black hole spacetimes with smooth horizons are known at the level of mathematics, we argue that the horizons of physical extreme black holes are effectively singular. Test particles encounter a singularity the moment they…
Vacuum bubbles may nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the bubbles quickly dissipate their kinetic energy; they come to rest with respect to the Hubble flow and eventually form…
The introduction of a relational time in quantum gravity naturally implies that pure quantum states evolve into mixed quantum states. We show, using a recently proposed concrete implementation, that the rate at which pure states naturally…
The formation of black holes or naked singularities is studied in a model in which a homogeneous time-dependent scalar field with an exponential potential couples to four dimensional gravity with negative cosmological constant. An analytic…
We establish the relationship between the space-time structure of regular spherically-symmetrical black holes and the character of violation of the strong energy condition (SEC). It is shown that it is violated in any static region under…
We consider self-interacting scalar fields coupled to gravity. Two classes of exact solutions to Einstein's equations are obtained: the first class corresponds to the minimal coupling, the second one to the conformal coupling. One of the…
We investigate the effect of gravitational back-reaction on the black hole evaporation process. The standard derivation of Hawking radiation is re-examined and extended by including gravitational interactions between the infalling matter…