17,657 research outputs found
Non-spherical sources of static gravitational fields: investigating the boundaries of the no-hair theorem
A new, globally regular model describing a static, non spherical gravitating
object in General Relativity is presented. The model is composed by a vacuum
Weyl--Levi-Civita special field - the so called gamma metric - generated by a
regular static distribution of mass-energy. Standard requirements of physical
reasonableness such as, energy, matching and regularity conditions are
satisfied. The model is used as a toy in investigating various issues related
to the directional behavior of naked singularities in static spacetimes and the
blackhole (Schwarschild) limit.Comment: 10 pages, 2 figure
Dynamics of Viscous Dissipative Plane Symmetric Gravitational Collapse
We present dynamical description of gravitational collapse in view of Misner
and Sharp's formalism. Matter under consideration is a complicated fluid
consistent with plane symmetry which we assume to undergo dissipation in the
form of heat flow, radiation, shear and bulk viscosity. Junction conditions are
studied for a general spacetime in the interior and Vaidya spacetime in the
exterior regions. Dynamical equations are obtained and coupled with causal
transport equations derived in context of Mller Israel Stewart
theory. The role of dissipative quantities over collapse is investigated.Comment: 17 pages, accepted for publication in Gen. Relativ. Gra
A source of a quasi--spherical space--time: The case for the M--Q solution
We present a physically reasonable source for an static, axially--symmetric
solution to the Einstein equations. Arguments are provided, supporting our
belief that the exterior space--time produced by such source, describing a
quadrupole correction to the Schwarzschild metric, is particularly suitable
(among known solutions of the Weyl family) for discussing the properties of
quasi--spherical gravitational fields.Comment: 34 pages, 9 figures. To appear in GR
Mixed potentials in radiative stellar collapse
We study the behaviour of a radiating star when the interior expanding,
shearing fluid particles are traveling in geodesic motion. We demonstrate that
it is possible to obtain new classes of exact solutions in terms of elementary
functions without assuming a separable form for the gravitational potentials or
initially fixing the temporal evolution of the model unlike earlier treatments.
A systematic approach enables us to write the junction condition as a Riccati
equation which under particular conditions may be transformed into a separable
equation. New classes of solutions are generated which allow for mixed spatial
and temporal dependence in the metric functions. We regain particular models
found previously from our general classes of solutions.Comment: 10 pages, To appear in J. Math. Phy
Dissipative fluids out of hydrostatic equilibrium
In the context of the M\"{u}ller-Israel-Stewart second order phenomenological
theory for dissipative fluids, we analyze the effects of thermal conduction and
viscosity in a relativistic fluid, just after its departure from hydrostatic
equilibrium, on a time scale of the order of relaxation times. Stability and
causality conditions are contrasted with conditions for which the ''effective
inertial mass'' vanishes.Comment: 21 pages, 1 postscript figure (LaTex 2.09 and epsfig.sty required)
Submitted to Classical and Quantum Gravit
Charged Cylindrical Collapse of Anisotropic Fluid
Following the scheme developed by Misner and Sharp, we discuss the dynamics
of gravitational collapse. For this purpose, an interior cylindrically
symmetric spacetime is matched to an exterior charged static cylindrically
symmetric spacetime using the Darmois matching conditions. Dynamical equations
are obtained with matter dissipating in the form of shear viscosity. The effect
of charge and dissipative quantities over the cylindrical collapse are studied.
Finally, we show that homogeneity in energy density and conformal flatness of
spacetime are necessary and sufficient for each other.Comment: 19 pages, accepted for publication in Gen. Relativ. Gra
Effects of f(R) Model on the Dynamical Instability of Expansionfree Gravitational Collapse
Dark energy models based on f(R) theory have been extensively studied in
literature to realize the late time acceleration. In this paper, we have chosen
a viable f(R) model and discussed its effects on the dynamical instability of
expansionfree fluid evolution generating a central vacuum cavity. For this
purpose, contracted Bianchi identities are obtained for both the usual matter
as well as dark source. The term dark source is named to the higher order
curvature corrections arising from f(R) gravity. The perturbation scheme is
applied and different terms belonging to Newtonian and post Newtonian regimes
are identified. It is found that instability range of expansionfree fluid on
external boundary as well as on internal vacuum cavity is independent of
adiabatic index but depends upon the density profile, pressure
anisotropy and f(R) model.Comment: 26 pages, no figure. arXiv admin note: text overlap with
arXiv:1108.266
Radiating Shear-Free Gravitational Collapse with Charge
We present a new shear free model for the gravitational collapse of a
spherically symmetric charged body. We propose a dissipative contraction with
radiation emitted outwards. The Einstein field equations, using the junction
conditions and an ansatz, are integrated numerically. A check of the energy
conditions is also performed. We obtain that the charge delays the black hole
formation and it can even halt the collapse.Comment: 22 pages, 9 figures. It has been corrected several typos and included
several references. Accepted for publication in GR
Expansionfree Fluid Evolution and Skripkin Model in f(R) Theory
We consider the modified theory of gravity whose higher order
curvature terms are interpreted as a gravitational fluid or dark source. The
gravitational collapse of a spherically symmetric star, made up of locally
anisotropic viscous fluid, is studied under the general influence of the
curvature fluid. Dynamical equations and junction conditions are modified in
the context of f(R) dark energy and by taking into account the expansionfree
evolution of the self-gravitating fluid. As a particular example, the Skripkin
model is investigated which corresponds to isotropic pressure with constant
energy density. The results are compared with corresponding results in General
Relativity.Comment: 18 pages, accepted for publication Int. J. Mod. Phys.
Geodesics in a quasispherical spacetime: A case of gravitational repulsion
Geodesics are studied in one of the Weyl metrics, referred to as the M--Q
solution. First, arguments are provided, supporting our belief that this
space--time is the more suitable (among the known solutions of the Weyl family)
for discussing the properties of strong quasi--spherical gravitational fields.
Then, the behaviour of geodesics is compared with the spherically symmetric
situation, bringing out the sensitivity of the trajectories to deviations from
spherical symmetry. Particular attention deserves the change of sign in proper
radial acceleration of test particles moving radially along symmetry axis,
close to the surface, and related to the quadrupole moment of the
source.Comment: 30 pages late
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