283 research outputs found
Gravitational Collapse in Constant Potential Bath
We analyse here the gravitational collapse of directed null radiation in a
background with a constant potential such as one produced by a star system like
galaxy in which the collapsing object is immersed. Both naked singularities and
black holes are shown to be developing as the final outcome of the collapse. An
interesting feature that emerges is that a part of the naked singularity
spectrum in collapsing Vaidya region gets covered in the corresponding
dual-Vaidya region, which corresponds to the Vaidya directed null radiation
sitting in constant potential bath. The implications of such a result towards
the issue of stability of naked singularities are discussed.Comment: LaTex 12 Pages, 2 figures. To appear in Physical Review
Gravitational Collapse and Cosmological Constant
We consider here the effects of a non-vanishing cosmological term on the
final fate of a spherical inhomogeneous collapsing dust cloud. It is shown that
depending on the nature of the initial data from which the collapse evolves,
and for a positive value of the cosmological constant, we can have a globally
regular evolution where a bounce develops within the cloud. We characterize
precisely the initial data causing such a bounce in terms of the initial
density and velocity profiles for the collapsing cloud. In the cases otherwise,
the result of collapse is either formation of a black hole or a naked
singularity resulting as the end state of collapse. We also show here that a
positive cosmological term can cover a part of the singularity spectrum which
is visible in the corresponding dust collapse models for the same initial data.Comment: 18 pages, no figure
Black holes vs. naked singularities formation in collapsing Einstein's clusters
Non-static, spherically symmetric clusters of counter-rotating particles, of
the type first introduced by Einstein, are analysed here. The initial data
space can be parameterized in terms of three arbitrary functions, namely;
initial density, velocity and angular momentum profiles. The final state of
collapse, black hole or naked singularity, turns out to depend on the order of
the first non-vanishing derivatives of such functions at the centre. The work
extends recent results by Harada, Iguchi and Nakao.Comment: 13 pages, LaTeX format. To appear in Physical Review
Spherical Dust Collapse in Higher Dimensions
We consider here the question if it is possible to recover cosmic censorship
when a transition is made to higher dimensional spacetimes, by studying the
spherically symmetric dust collapse in an arbitrary higher spacetime dimension.
It is pointed out that if only black holes are to result as end state of a
continual gravitational collapse, several conditions must be imposed on the
collapsing configuration, some of which may appear to be restrictive, and we
need to study carefully if these can be suitably motivated physically in a
realistic collapse scenario. It would appear that in a generic higher
dimensional dust collapse, both black holes and naked singularities would
develop as end states as indicated by the results here. The mathematical
approach developed here generalizes and unifies the earlier available results
on higher dimensional dust collapse as we point out. Further, the dependence of
black hole or naked singularity end states as collapse outcomes, on the nature
of the initial data from which the collapse develops, is brought out explicitly
and in a transparent manner as we show here. Our method also allows us to
consider here in some detail the genericity and stability aspects related to
the occurrence of naked singularities in gravitational collapse.Comment: Revtex4, Title changed, To appear in Physical Review
Non-radial null geodesics in spherical dust collapse
The issue of the local visibility of the shell-focussing singularity in
marginally bound spherical dust collapse is considered from the point of view
of the existence of future-directed null geodesics with angular momentum which
emanate from the singularity. The initial data (i.e. the initial density
profile) at the onset of collapse is taken to be of class . Simple
necessary and sufficient conditions for the existence of a naked singularity
are derived in terms of the data. It is shown that there exist future-directed
non-radial null geodesics emanating from the singularity if and only if there
exist future-directed radial null geodesics emanating from the singularity.
This result can be interpreted as indicating the robustness of previous results
on radial geodesics, with respect to the presence of angular momentum.Comment: 26 pages, 1 figur
Negative Pressure and Naked Singularities in Spherical Gravitational Collapse
Assuming the weak energy condition, we study the nature of the non-central
shell-focussing singularity which can form in the gravitational collapse of a
spherical compact object in classical general relativity. We show that if the
radial pressure is positive, the singularity is covered by a horizon. For
negative radial pressures, the singularity will be covered if the ratio of
pressure to the density is greater than -1/3 and naked if this ratio is .Comment: 7 pages, LaTeX Fil
Naked Singularity Explosion
It is known that the gravitational collapse of a dust ball results in naked
singularity formation from an initial density profile which is physically
reasonable. In this paper, we show that explosive radiation is emitted during
the formation process of the naked singularity.Comment: 6 pages, 3 figures, Accepted for Publication in Phys. Rev. D as a
Rapid Communicatio
Comments on scalar-tensor representation of nonlocally corrected gravity
The scalar-tensor representation of nonlocally corrected gravity is
considered. Some special solutions of the vacuum background equations were
obtained that indicate to the nonequivalence of the initial theory and its
scalar-tensor representation.Comment: 6 pages, refs adde
On bouncing solutions in non-local gravity
A non-local modified gravity model with an analytic function of the
d'Alembert operator is considered. This model has been recently proposed as a
possible way of resolving the singularities problem in cosmology. We present an
exact bouncing solution, which is simpler compared to the already known one in
this model in the sense it does not require an additional matter to satisfy all
the gravitational equations.Comment: 5 pages; v2: matching the jounral versio
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