3,731 research outputs found
Spherically symmetric perfect fluid in area-radial coordinates
We study the spherically symmetric collapse of a perfect fluid using
area-radial coordinates. We show that analytic mass functions describe a static
regular centre in these coordinates. In this case, a central singularity can
not be realized without an infinite discontinuity in the central density. We
construct mass functions involving fluid dynamics at the centre and investigate
the relationship between those and the nature of the singularities.Comment: Accepted by CQG. LaTex file, 14 pages, no figure
Exact solution for scalar field collapse
We give an exact spherically symmetric solution for the Einstein-scalar field
system. The solution may be interpreted as an inhomogeneous dynamical scalar
field cosmology. The spacetime has a timelike conformal Killing vector field
and is asymptotically conformally flat. It also has black or white hole-like
regions containing trapped surfaces. We describe the properties of the apparent
horizon and comment on the relevance of the solution to the recently discovered
critical behaviour in scalar field collapse.Comment: 10 pages(Latex) (2 figures available upon request), Alberta-Thy-4-9
A Striking Confluence Between Theory and Observations of High-Mass X-ray Binary Pulsars
We analyse the most powerful X-ray outbursts from neutron stars in ten
Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray
sources. Most of the outbursts rise to which is about the level of
the Eddington luminosity, while the rest and more powerful outbursts also
appear to recognize that limit when their emissions are assumed to be
anisotropic and beamed toward our direction. We use the measurements of pulsar
spin periods and their derivatives to calculate the X-ray
luminosities in their faintest accreting ("propeller") states. In four
cases with unknown , we use the lowest observed X-ray luminosities,
which only adds to the heterogeneity of the sample. Then we calculate the
ratios and we obtain an outstanding confluence of theory and
observations from which we conclude that work done on both fronts is accurate
and the results are trustworthy: sources known to reside on the lowest
Magellanic propeller line are all located on/near that line, whereas other
sources jump higher and reach higher-lying propeller lines. These jumps can be
interpreted in only one way, higher-lying pulsars have stronger surface
magnetic fields in agreement with empirical results in which and
values were not used.Comment: Added LMC X-4 and commented on the cyclotron absorption line of SMC
X-2. 4 pages, 1 figure, 2 tables, submitted to MNRAS
The spherically symmetric collapse of a massless scalar field
We report on a numerical study of the spherically symmetric collapse of a
self-gravitating massless scalar field. Earlier results of Choptuik(1992, 1994)
are confirmed. The field either disperses to infinity or collapses to a black
hole, depending on the strength of the initial data. For evolutions where the
strength is close to but below the strength required to form a black hole, we
argue that there will be a region close to the axis where the scalar curvature
and field energy density can reach arbitrarily large levels, and which is
visible to distant observersComment: 23 pages, 16 figures, uuencoded gzipped postscript This version omits
2 pages of figures. This file, the two pages of figures and the complete
paper are available at ftp://ftp.damtp.cam.ac.uk/pub/gr/rsh100
The formation of black holes in spherically symmetric gravitational collapse
We consider the spherically symmetric, asymptotically flat Einstein-Vlasov
system. We find explicit conditions on the initial data, with ADM mass M, such
that the resulting spacetime has the following properties: there is a family of
radially outgoing null geodesics where the area radius r along each geodesic is
bounded by 2M, the timelike lines are incomplete, and for r>2M
the metric converges asymptotically to the Schwarzschild metric with mass M.
The initial data that we construct guarantee the formation of a black hole in
the evolution. We also give examples of such initial data with the additional
property that the solutions exist for all and all Schwarzschild time,
i.e., we obtain global existence in Schwarzschild coordinates in situations
where the initial data are not small. Some of our results are also established
for the Einstein equations coupled to a general matter model characterized by
conditions on the matter quantities.Comment: 36 pages. A corollary on global existence in Schwarzschild
coordinates for data which are not small is added together with minor
modification
Final fate of spherically symmetric gravitational collapse of a dust cloud in Einstein-Gauss-Bonnet gravity
We give a model of the higher-dimensional spherically symmetric gravitational
collapse of a dust cloud in Einstein-Gauss-Bonnet gravity. A simple formulation
of the basic equations is given for the spacetime with a perfect fluid and a cosmological constant. This is a
generalization of the Misner-Sharp formalism of the four-dimensional
spherically symmetric spacetime with a perfect fluid in general relativity. The
whole picture and the final fate of the gravitational collapse of a dust cloud
differ greatly between the cases with and . There are two
families of solutions, which we call plus-branch and the minus-branch
solutions. Bounce inevitably occurs in the plus-branch solution for ,
and consequently singularities cannot be formed. Since there is no trapped
surface in the plus-branch solution, the singularity formed in the case of
must be naked. In the minus-branch solution, naked singularities are
massless for , while massive naked singularities are possible for
. In the homogeneous collapse represented by the flat
Friedmann-Robertson-Walker solution, the singularity formed is spacelike for , while it is ingoing-null for . In the inhomogeneous collapse with
smooth initial data, the strong cosmic censorship hypothesis holds for and for depending on the parameters in the initial data, while a
naked singularity is always formed for . These naked
singularities can be globally naked when the initial surface radius of the dust
cloud is fine-tuned, and then the weak cosmic censorship hypothesis is
violated.Comment: 23 pages, 1 figure, final version to appear in Physical Review
Particle Creation in the Marginally Bound, Self Similar Collapse of Inhomogeneous Dust
We consider the evaporation of the (shell focusing) naked singularity formed
during the self-similar collapse of a marginally bound inhomogeneous dust
cloud, in the geometric optics approximation. We show that, neglecting the back
reaction of the spacetime, the radiation on \scrip tends to infinity as the
Cauchy Horizon is approached. Two consequences can be expected from this
result: (a) that the back reaction of spacetime will be large and eventually
halt the formation of a naked singularity thus preserving the Cosmic Censorship
Hypothesis and (b) matter attempting to collapse into a naked singularity will
radiate away energy at an intense rate, thereby possibly providing experimental
signatures of quantum effects in curved spacetimes.Comment: 18 pages, 4 figures. Version to appear in Nucl. Phys.
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