4,179 research outputs found
Thermodynamics of toroidal black holes
The thermodynamical properties of toroidal black holes in the grand canonical
ensemble are investigated using York's formalism. The black hole is enclosed in
a cavity with finite radius where the temperature and electrostatic potential
are fixed. The boundary conditions allow one to compute the relevant
thermodynamical quantities, e.g. thermal energy, entropy and specific heat.
This black hole is thermodynamically stable and dominates the grand partition
function. This means that there is no phase transition, as the one encountered
for spherical black holes.Comment: 11 pages, 2 eps figures, revte
Collapsing and static thin massive charged dust shells in a Reissner-Nordstr\"om black hole background in higher dimensions
The problem of a spherically symmetric charged thin shell of dust collapsing
gravitationally into a charged Reissner-Nordstr\"om black hole in spacetime
dimensions is studied within the theory of general relativity. Static charged
shells in such a background are also analyzed. First a derivation of the
equation of motion of such a shell in a -dimensional spacetime is given.
Then a proof of the cosmic censorship conjecture in a charged collapsing
framework is presented, and a useful constraint which leads to an upper bound
for the rest mass of a charged shell with an empty interior is derived. It is
also proved that a shell with total mass equal to charge, i.e., an extremal
shell, in an empty interior, can only stay in neutral equilibrium outside its
gravitational radius. This implies that it is not possible to generate a
regular extremal black hole by placing an extremal dust thin shell within its
own gravitational radius. Moreover, it is shown, for an empty interior, that
the rest mass of the shell is limited from above. Then several types of
behavior of oscillatory charged shells are studied. In the presence of a
horizon, it is shown that an oscillatory shell always enters the horizon and
reemerges in a new asymptotically flat region of the extended
Reissner-Nordstr\"om spacetime. On the other hand, for an overcharged interior,
i.e., a shell with no horizons, an example showing that the shell can achieve a
stable equilibrium position is presented. The results presented have
applications in brane scenarios with extra large dimensions, where the creation
of tiny higher dimensional charged black holes in current particle accelerators
might be a real possibility, and generalize to higher dimensions previous
calculations on the dynamics of charged shells in four dimensions.Comment: 21 pages, 2 figure
Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop and cosmic censorship conjectures
Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.Comment: 4 pages, Revtex Journal: to appear in Physical Review
Gravitational collapse to toroidal, cylindrical and planar black holes
Gravitational collapse of non-spherical symmetric matter leads inevitably to
non-static external spacetimes. It is shown here that gravitational collapse of
matter with toroidal topology in a toroidal anti-de Sitter background proceeds
to form a toroidal black hole. According to the analytical model presented, the
collapsing matter absorbs energy in the form of radiation (be it scalar,
neutrinos, electromagnetic, or gravitational) from the exterior spacetime. Upon
decompactification of one or two coordinates of the torus one gets collapsing
solutions of cylindrical or planar matter onto black strings or black
membranes, respectively. The results have implications on the hoop conjecture.Comment: 6 pages, Revtex, modifications in the title and in the interpretation
of some results, to appear in Physical Review
The Three-Dimensional BTZ Black Hole as a Cylindrical System in Four-Dimensional General Relativity
It is shown how to transform the three dimensional BTZ black hole into a four
dimensional cylindrical black hole (i.e., black string) in general relativity.
This process is identical to the transformation of a point particle in three
dimensions into a straight cosmic string in four dimensions.Comment: Latex, 9 page
The Tolman-Bondi--Vaidya Spacetime: matching timelike dust to null dust
The Tolman-Bondi and Vaidya solutions are two solutions to Einstein equations
which describe dust particles and null fluid, respectively. We show that it is
possible to match the two solutions in one single spacetime, the
Tolman-Bondi--Vaidya spacetime. The new spacetime is divided by a null surface
with Tolman-Bondi dust on one side and Vaidya fluid on the other side. The
differentiability of the spacetime is discussed. By constructing a specific
solution, we show that the metric across the null surface can be at least
and the stress-energy tensor is continuous.Comment: 5 pages, no figur
Local conditions for the generalized covariant entropy bound
A set of sufficient conditions for the generalized covariant entropy bound
given by Strominger and Thompson is as follows: Suppose that the entropy of
matter can be described by an entropy current . Let be any null
vector along and . Then the generalized bound can be
derived from the following conditions: (i) , where
s'=k^a\grad_a s and is the stress energy tensor; (ii) on the initial
2-surface , , where is the expansion of
. We prove that condition (ii) alone can be used to divide a spacetime
into two regions: The generalized entropy bound holds for all light sheets
residing in the region where and fails for those in the region
where . We check the validity of these conditions in FRW flat
universe and a scalar field spacetime. Some apparent violations of the entropy
bounds in the two spacetimes are discussed. These holographic bounds are
important in the formulation of the holographic principle.Comment: 10 pages, 7 figure
Two-Dimensional Black Holes and Planar General Relativity
The Einstein-Hilbert action with a cosmological term is used to derive a new
action in 1+1 spacetime dimensions. It is shown that the two-dimensional theory
is equivalent to planar symmetry in General Relativity. The two-dimensional
theory admits black holes and free dilatons, and has a structure similar to
two-dimensional string theories. Since by construction these solutions also
solve Einstein's equations, such a theory can bring two-dimensional results
into the four-dimensional real world. In particular the two-dimensional black
hole is also a black hole in General Relativity.Comment: 11 pages, plainte
Quasinormal modes and stability of the rotating acoustic black hole: numerical analysis
The study of the quasinormal modes (QNMs) of the 2+1 dimensional rotating
draining bathtub acoustic black hole, the closest analogue found so far to the
Kerr black hole, is performed. Both the real and imaginary parts of the
quasinormal (QN) frequencies as a function of the rotation parameter B are
found through a full non-linear numerical analysis. Since there is no change in
sign in the imaginary part of the frequency as B is increased we conclude that
the 2+1 dimensional rotating draining bathtub acoustic black hole is stable
against small perturbations.Comment: 6 pages, ReVTeX4. v2. References adde
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