606 research outputs found
Backreaction of accreting matter onto a black hole in the Eddington-Finkelstein coordinates
We study backreaction of accreting matter onto a spherically symmetric black
hole in a perturbative way, when accretion is in a quasi-steady state. General
expressions for corrections to the metric coefficients are found in the
Eddington-Finkelstein coordinates. It is shown that near the horizon of a black
hole, independently of the form of the energy-momentum tensor, the leading
corrections to the metric are of the Vaidya form. The relation to other
solutions is discussed and particular examples are presented.Comment: 12 pages, v.2: references added, typos corrected, matches published
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Global topological k-defects
We consider global topological defects in symmetry breaking models with a
non-canonical kinetic term. Apart from a mass parameter entering the potential,
one additional dimensional parameter arises in such models -- a ``kinetic''
mass. The properties of defects in these models are quite different from
``standard'' global domain walls, vortices and monopoles, if their kinetic mass
scale is smaller than their symmetry breaking scale. In particular, depending
on the concrete form of the kinetic term, the typical size of such a defect can
be either much larger or much smaller than the size of a standard defect with
the same potential term. The characteristic mass of a non-standard defect,
which might have been formed during a phase transition in the early universe,
depends on both the temperature of a phase transition and the kinetic mass.Comment: 7 pages, 3 figures; v2: references added, matches the published
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Ultra-hard fluid and scalar field in the Kerr-Newman metric
An analytic solution for the accretion of ultra-hard perfect fluid onto a
moving Kerr-Newman black hole is found. This solution is a generalization of
the previously known solution by Petrich, Shapiro and Teukolsky for a Kerr
black hole. Our solution is not applicable for an extreme black hole due to
violation of the test fluid approximation. We also present a stationary
solution for a massless scalar field in the metric of a Kerr-Newman naked
singularity.Comment: 9 pages, 3 figures, revtex4; v2: presentation improved, figures
added, matches published versio
Black holes in the presence of dark energy
The new, rapidly developing field of theoretical research --- studies of dark
energy interacting with black holes (and, in particular, accreting onto black
holes) --- is reviewed. The term `dark energy' is meant to cover a wide range
of field theory models, as well as perfect fluids with various equations of
state, including cosmological dark energy. Various accretion models are
analyzed in terms of the simplest test field approximation or by allowing back
reaction on the black-hole metric. The behavior of various types of dark energy
in the vicinity of Schwarzschild and electrically charged black holes is
examined. Nontrivial effects due to the presence of dark energy in the black
hole vicinity are discussed. In particular, a physical explanation is given of
why the black hole mass decreases when phantom energy is being accreted, a
process in which the basic energy conditions of the famous theorem of
nondecreasing horizon area in classical black holes are violated. The
theoretical possibility of a signal escaping from beneath the black hole event
horizon is discussed for a number of dark energy models. Finally, the violation
of the laws of thermodynamics by black holes in the presence of noncanonical
fields is considered.Comment: 25 pages, 10 figures, review pape
Gravitational radiation from rotating monopole-string systems
We study the gravitational radiation from a rotating monopole-antimonopole
pair connected by a string. While at not too high frequencies the emitted
gravitational spectrum is described asymptotically by , the
spectrum is exponentially suppressed in the high-frequency limit, . Below , the emitted spectrum of gravitational
waves is very similar to the case of an oscillating monopole pair connected by
a string, and we argue therefore that the spectrum found holds approximately
for any moving monopole-string system. As application, we discuss the
stochastic gravitational wave background generated by monopole-antimonopole
pairs connected by strings in the early Universe and gravitational wave bursts
emitted at present by monopole-string networks. We confirm that advanced
gravitational wave detectors have the potential to detect a signal for string
tensions as small as .Comment: 8 pages, 2 figures, revtex4; v2: minor corrections, matches published
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Stationary Configurations Imply Shift Symmetry: No Bondi Accretion for Quintessence / k-Essence
In this paper we show that, for general scalar fields, stationary
configurations are possible for shift symmetric theories only. This symmetry
with respect to constant translations in field space should either be manifest
in the original field variables or reveal itself after an appropriate field
redefinition. In particular this result implies that neither k-Essence nor
Quintessence can have exact steady state / Bondi accretion onto Black Holes. We
also discuss the role of field redefinitions in k-Essence theories. Here we
study the transformation properties of observables and other variables in
k-Essence and emphasize which of them are covariant under field redefinitions.
Finally we find that stationary field configurations are necessarily linear in
Killing time, provided that shift symmetry is realized in terms of these field
variables.Comment: 8 page
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