Related papers: Black holes
After reviewing the shortcomings of existing definitions used to characterize the boundary of a black hole, we present a new method for its characterization. This definition could potentially be applied to locate the boundary of general…
There are reasons (which we enumerate) to think that an infinite extra dimension will harbor a black hole. In this case, brane-localized modes of gravity and gauge fields become quasilocalized, and light from a distant object can become…
The growth of supermassive black holes by merging and accretion in hierarchical models of galaxy formation is studied by means of Monte Carlo simulations. A tight linear relation between masses of black holes and masses of bulges arises if…
We develop the general formalism for joining, splitting and interconnection of closed and open strings. As an application, we study examples of fundamental cosmic string collisions leading to gravitational collapse. We find that the…
The supermassive black hole at the center of a distant galaxy can be weighed, in rare but realistic cases, when the galaxy acts as a strong gravitational lens. The central image that should be produced by the lens is either destroyed or…
The existence of exact solutions which represent a lattice of black holes at a scalar-field-dominated cosmological bounce suggests that black holes could persist through successive eras of a cyclic cosmology. Here we explore some remarkable…
A general definition of a black hole is given, and general `laws of black-hole dynamics' derived. The definition involves something similar to an apparent horizon, a trapping horizon, defined as a hypersurface foliated by marginal surfaces…
Three dimensional black holes in a generalized dilaton gravity action theory are analysed. The theory is specified by two fields, the dilaton and the graviton, and two parameters, the cosmological constant and the Brans-Dicke parameter. It…
What is going on (as of August 2008) at the interface between theoretical general relativity, string-inspired models, and observational astrophysics? Quite a lot. In this mini-survey I will make a personal choice and focus on four specific…
The dimensionless entropy, ${\cal S} \equiv S/k$, of the visible universe, taken as a sphere of radius 50 billion light years with the Earth at its "center", is discussed. An upper limit ($10^{112}$), and a lower limit ($10^{102}$), for…
A discussion at a Scientific American level of the idea that the constituents of the dark mater in galactic halos are primordial intermediate-mass black holes with masses between ten and one hundred thousand times the solar mass.
A definition of a Newtonian black hole is possible which incorporates the mass-energy equivalence from special relativity. However, exploiting a double spherical shell model, it will be shown that the ensuing gravitational self-energy and…
The conditions are clarified under which regular (i.e., singularity-free) black holes can exist. It is shown that in a large class of spacetimes that satisfy the weak energy condition the existence of a regular black hole requires topology…
A new theorem for black holes is established. The mass of a black hole depends on where the observer is. The horizon mass theorem states that for all black holes: neutral, charged or rotating, the horizon mass is always twice the…
In theories with large extra dimensions and TeV-scale gravity, black holes are copiously produced in particle collisions at energies well above the Planck scale. I briefly review some recent work on the phenomenology of this process, with…
What does a black hole look like? In 1+3 spacetime dimensions, the optical appearance of a black hole is a bidimensional region in the observer's sky often called the black hole shadow, as supported by the EHT observations. In higher…
Some approaches to quantization of the horizon area of black holes are discussed. The maximum entropy of a quantized surface is demonstrated to be proportional to the surface area in the classical limit. This result is valid for a rather…
Three recent papers have been collected here, discussing the possibility and properties of periodic modulation of a signal from accreting black holes surrounded by orbiting clumps of gas.
In the local universe, black hole masses have been inferred from the observed increase in the velocities of stars at the centres of their host galaxies. So far, masses of supermassive black holes in the early universe have only been…
The nature of dark matter is still an open problem. The simplest assumption is that gravity is the only force coupled certainly to dark matter and thus the micro black holes could be a viable candidate. We investigated the possibility of…