53 research outputs found
Appearance of the central singularity in spherical collapse
We analyze here the structure of non-radial nonspacelike geodesics
terminating in the past at a naked singularity formed as the end state of
inhomogeneous dust collapse. The spectrum of outgoing nonspacelike null
geodesics is examined analytically. The local and global visibility of the
singularity is also examined by integrating numerically the null geodesics
equations. The possible implications of existence of such families towards the
appearance of the star in late stages of gravitational collapse are considered.
It is seen that the outgoing non-radial geodesics give an appearance to the
naked central singularity as that of an expanding ball whose radius reaches a
maximum before the star goes within its apparent horizon. The radiated energy
(along the null geodesics) is shown to decay very sharply in the neighbourhood
of the singularity. Thus the total energy escaping via non-radial null
geodesics from the naked central singularity vanishes in the scenario
considered here.Comment: 25 pages, 6 figure
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
Formation of a galaxy with a central black hole in the Lemaitre-Tolman model
We construct two models of the formation a galaxy with a central black hole,
starting from a small initial fluctuation at recombination. This is an
application of previously developed methods to find a Lemaitre-Tolman model
that evolves from a given initial density or velocity profile to a given final
density profile. We show that the black hole itself could be either a collapsed
object, or a non-vacuum generalisation of a full Schwarzschild-Kruskal-Szekeres
wormhole. Particular attention is paid to the black hole's apparent and event
horizons.Comment: REVTeX, 22 pages including 11 figures (25 figure files). Replacement
has minor changes in response to the referee, and editorial corrections. To
appear in PR
Higher dimensional inhomogeneous dust collapse and cosmic censorship
We investigate the occurrence and nature of a naked singularity in the
gravitational collapse of an inhomogeneous dust cloud described by higher
dimensional Tolman-Bondi space-times. The naked singularities are found to be
gravitationally strong in the sense of Tipler. Higher dimensions seem to favour
black holes rather than naked singularities.Comment: 15 pages, LaTeX, 1 figure, 2 table
Higher dimensional dust collapse with a cosmological constant
The general solution of the Einstein equation for higher dimensional (HD)
spherically symmetric collapse of inhomogeneous dust in presence of a
cosmological term, i.e., exact interior solutions of the Einstein field
equations is presented for the HD Tolman-Bondi metrics imbedded in a de Sitter
background. The solution is then matched to exterior HD Scwarschild-de Sitter.
A brief discussion on the causal structure singularities and horizons is
provided. It turns out that the collapse proceed in the same way as in the
Minkowski background, i.e., the strong curvature naked singularities form and
that the higher dimensions seem to favor black holes rather than naked
singularities.Comment: 7 Pages, no figure
Gravitational collapse of a Hagedorn fluid in Vaidya geometry
The gravitational collapse of a high-density null charged matter fluid,
satisfying the Hagedorn equation of state, is considered in the framework of
the Vaidya geometry. The general solution of the gravitational field equations
can be obtained in an exact parametric form. The conditions for the formation
of a naked singularity, as a result of the collapse of the compact object, are
also investigated. For an appropriate choice of the arbitrary integration
functions the null radial outgoing geodesic, originating from the shell
focussing central singularity, admits one or more positive roots. Hence a
collapsing Hagedorn fluid could end either as a black hole, or as a naked
singularity. A possible astrophysical application of the model, to describe the
energy source of gamma-ray bursts, is also considered.Comment: 14 pages, 2 figures, to appear in Phys. Rev.
Radial asymptotics of Lemaitre-Tolman-Bondi dust models
We examine the radial asymptotic behavior of spherically symmetric
Lemaitre-Tolman-Bondi dust models by looking at their covariant scalars along
radial rays, which are spacelike geodesics parametrized by proper length
, orthogonal to the 4-velocity and to the orbits of SO(3). By introducing
quasi-local scalars defined as integral functions along the rays, we obtain a
complete and covariant representation of the models, leading to an initial
value parametrization in which all scalars can be given by scaling laws
depending on two metric scale factors and two basic initial value functions.
Considering regular "open" LTB models whose space slices allow for a diverging
, we provide the conditions on the radial coordinate so that its
asymptotic limit corresponds to the limit as . The "asymptotic
state" is then defined as this limit, together with asymptotic series expansion
around it, evaluated for all metric functions, covariant scalars (local and
quasi-local) and their fluctuations. By looking at different sets of initial
conditions, we examine and classify the asymptotic states of parabolic,
hyperbolic and open elliptic models admitting a symmetry center. We show that
in the radial direction the models can be asymptotic to any one of the
following spacetimes: FLRW dust cosmologies with zero or negative spatial
curvature, sections of Minkowski flat space (including Milne's space), sections
of the Schwarzschild--Kruskal manifold or self--similar dust solutions.Comment: 44 pages (including a long appendix), 3 figures, IOP LaTeX style.
Typos corrected and an important reference added. Accepted for publication in
General Relativity and Gravitatio
Proteomic Analysis Reveals Age-related Changes in Tendon Matrix Composition, with Age- and Injury-specific Matrix Fragmentation
Energy storing tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT), are highly prone to injury, the incidence of which increases with aging. The cellular and molecular mechanisms that result in increased injury in aged tendons are not well established but are thought to result in altered matrix turnover. However, little attempt has been made to fully characterize the tendon proteome nor determine how the abundance of specific tendon proteins changes with aging and/or injury. The aim of this study was, therefore, to assess the protein profile of normal SDFTs from young and old horses using label-free relative quantification to identify differentially abundant proteins and peptide fragments between age groups. The protein profile of injured SDFTs from young and old horses was also assessed. The results demonstrate distinct proteomic profiles in young and old tendon, with alterations in the levels of proteins involved in matrix organization and regulation of cell tension. Furthermore, we identified several new peptide fragments (neopeptides) present in aged tendons, suggesting that there are age-specific cleavage patterns within the SDFT. Proteomic profile also differed between young and old injured tendon, with a greater number of neopeptides identified in young injured tendon. This study has increased the knowledge of molecular events associated with tendon aging and injury, suggesting that maintenance and repair of tendon tissue may be reduced in aged individuals and may help to explain why the risk of injury increases with aging
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