638 research outputs found
On trapped surface formation in gravitational collapse II
Further to our consideration on trapped surfaces in gravitational collapse,
where pressures were allowed to be negative while satisfying weak energy
condition to avoid trapped surface formation, we discuss here several other
attempts of similar nature in this direction. Certain astrophysical aspects are
pointed out towards examining the physical realization of such a possibility in
realistic gravitational collapse
Gravitational collapse of an isentropic perfect fluid with a linear equation of state
We investigate here the gravitational collapse end states for a spherically
symmetric perfect fluid with an equation of state . It is shown that
given a regular initial data in terms of the density and pressure profiles at
the initial epoch from which the collapse develops, the black hole or naked
singularity outcomes depend on the choice of rest of the free functions
available, such as the velocities of the collapsing shells, and the dynamical
evolutions as allowed by Einstein equations. This clarifies the role that
equation of state and initial data play towards determining the final fate of
gravitational collapse.Comment: 7 Pages, Revtex4, To appear in Classical and Quantum Gravit
Stability of Naked Singularity arising in gravitational collapse of Type I matter fields
Considering gravitational collapse of Type I matter fields, we prove that,
given an arbitrary - mass function and a -
function (through the corresponding - metric function
), there exist infinitely many choices of energy distribution
function such that the `true' initial data () leads
the collapse to the formation of naked singularity. We further prove that the
occurrence of such a naked singularity is stable with respect to small changes
in the initial data. We remark that though the initial data leading to both
black hole and naked singularity form a "big" subset of the true initial data
set, their occurrence is not generic. The terms `stability' and `genericity'
are appropriately defined following the theory of dynamical systems. The
particular case of radial pressure has been illustrated in details
to get clear picture of how naked singularity is formed and how, it is stable
with respect to initial data.Comment: 16 pages, no figure, Latex, submitted to Praman
Gravitational collapse from smooth initial data with vanishing radial pressure
We study here the spherical gravitational collapse assuming initial data to
be necessarily smooth, as motivated by the requirements based on physical
reasonableness. A tangential pressure model is constructed and analyzed in
order to understand the final fate of collapse explicitly in terms of the
density and pressure parameters at the initial epoch from which the
collapsedevelops. It is seen that both black holes and naked singularities are
produced as collapse end states even when the initial data is smooth. We show
that the outcome is decided entirely in terms of the initial data, as given by
density, pressure and velocity profiles at the initial epoch, from which the
collapse evolves.Comment: 10 pages,3 figures,revtex4,Revised Versio
Quantum evaporation of a naked singularity
We investigate here quantum effects in gravitational collapse of a scalar
field model which classically leads to a naked singularity. We show that
non-perturbative semi-classical modifications near the singularity, based on
loop quantum gravity, give rise to a strong outward flux of energy. This leads
to the dissolution of the collapsing cloud before the singularity can form.
Quantum gravitational effects thus censor naked singularities by avoiding their
formation. Further, quantum gravity induced mass flux has a distinct feature
which may lead to a novel observable signature in astrophysical bursts.Comment: 4 pages, 2 figures. Minor changes to match published version in
Physical Review Letter
A Time-Like Naked Singularity
We construct a class of spherically symmetric collapse models in which a
naked singularity may develop as the end state of collapse. The matter
distribution considered has negative radial and tangential pressures, but the
weak energy condition is obeyed throughout. The singularity forms at the center
of the collapsing cloud and continues to be visible for a finite time. The
duration of visibility depends on the nature of energy distribution. Hence the
causal structure of the resulting singularity depends on the nature of the mass
function chosen for the cloud. We present a general model in which the naked
singularity formed is timelike, neither pointlike nor null. Our work represents
a step toward clarifying the necessary conditions for the validity of the
Cosmic Censorship Conjecture.Comment: 4 pages, Revtex4, To appear in Physical Review
Role of initial data in spherical collapse
We bring out here the role of initial data in causing the black hole and
naked singularity phases as the final end state of a continual gravitational
collapse. The collapse of a type I general matter field is considered, which
includes most of the known physical forms of matter. It is shown that given the
distribution of the density and pressure profiles at the initial surface from
which the collapse evolves, there is a freedom in choosing rest of the free
functions, such as the velocities of the collapsing shells, so that the end
state could be either a black hole or a naked singularity depending on this
choice. It is thus seen that it is the initial data that determines the end
state of spherical collapse in terms of these outcomes, and we get a good
picture of how these phases come about.Comment: 5 pages, Revtex4, Revised version, To appear in Physical Review
Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions
We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.Comment: Accepted for publication in CQ
Cosmic Censorship in Higher dimension II
Generalizing earlier results on dust collapse in higher dimensions, we show
here that cosmic censorship can be restored in gravitational collapse with
tangential pressure present if we take the spacetime dimension to be .
This is under conditions to be motivated physically, such as the smoothness of
initial data from which the collapse develops. The models considered here
incorporating a non-zero tangential pressure include the Einstein cluster
spacetime.Comment: 7 pages,1 figure,revtex
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