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Pinheiro G.,Observatorio Nacional | Pinheiro G.,State University of Rio de Janeiro | Chan R.,Coordenacao de Astronomia e Astrofisica
General Relativity and Gravitation | Year: 2013

We present here a new shear free model for the gravitational collapse of a spherically symmetric charged body. We propose a dissipative contraction with radiation emitted outwards represented by the Vaidya-Reissner-Nordström metric. 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 Reissner-Nordström black hole formation and it can even prevent the collapse. © 2012 Springer Science+Business Media New York.


Goldoni O.,State University of Rio de Janeiro | Da Silva M.F.A.,State University of Rio de Janeiro | Pinheiro G.,Federal University of Rio de Janeiro | Chan R.,Coordenacao de Astronomia e Astrofisica
International Journal of Modern Physics D | Year: 2014

In this paper, we have studied nonstationary radiative spherically symmetric spacetime, in general covariant theory (U(1) extension) of Hořava-Lifshitz (HL) gravity without the projectability condition and in the infrared (IR) limit. The Newtonian prepotential φ was assumed null. We have shown that there is not the analogue of the Vaidya's solution in the Hořava-Lifshitz Theory (HLT), as we know in the General Relativity Theory (GRT). Therefore, we conclude that the gauge field A should interact with the null radiation field of the Vaidya's spacetime in the HLT. © 2014 World Scientific Publishing Company.


Chan R.,Coordenacao de Astronomia e Astrofisica | Da Silva M.F.A.,State University of Rio de Janeiro | Brandt C.F.C.,State University of Rio de Janeiro
International Journal of Modern Physics D | Year: 2014

We study the evolution of an anisotropic shear-free fluid with heat flux and kinematic self-similarity of the second kind. We found a class of solution to the Einstein field equations by assuming that the part of the tangential pressure which is explicitly time-dependent of the fluid is zero and that the fluid moves along timelike geodesics. The energy conditions, geometrical and physical properties of the solutions are studied. The energy conditions are all satisfied at the beginning of the collapse but when the system approaches the singularity the energy conditions are violated, allowing for the appearance of an attractive phantom energy. We have found that, depending on the self-similar parameter α and the geometrical radius, they may represent a naked singularity. We speculate that the apparent horizon disappears due to the emergence of exotic energy at the end of the collapse, or due to the characteristics of null acceleration systems as shown by recent work. © 2014 World Scientific Publishing Company.


Chan R.,Coordenacao de Astronomia e Astrofisica | Da Silva M.F.A.,State University of Rio de Janeiro | Villas Da Rocha J.F.,Rio de Janeiro State Federal University | Wang A.,Baylor University
Journal of Cosmology and Astroparticle Physics | Year: 2011

Considering a Vaidya exterior spacetime, we study dynamical models of prototype gravastars, made of an infinitely thin spherical shell of a perfect fluid with the equation of state p = σ, enclosing an interior de Sitter spacetime. We show explicitly that the final output can be a black hole, an unstable gravastar, a stable gravastar or a "bounded excursion" gravastar, depending on how the mass of the shell evolves in time, the cosmological constant and the initial position of the dynamical shell. This work presents, for the first time in the literature, a gravastar that emits radiation. © 2011 IOP Publishing Ltd and SISSA.


Pinheiro G.,Observatorio Nacional | Chan R.,Coordenacao de Astronomia e Astrofisica
General Relativity and Gravitation | Year: 2011

A new model is proposed to a collapsing star consisting of an initial inhomogeneous energy density and anisotropic pressure fluid with shear, radial heat flow and outgoing radiation. In previous papers one of us has always assumed an initial star with homogeneous energy density. The aim of this work is to generalize the previous models by introducing an initial inhomogeneous energy density and compare it to the initial homogeneous energy density collapse model. We will show the differences between these models in the evolution of all physical quantities that characterizes the gravitational collapse. The behavior of the energy density, pressure, mass, luminosity and the effective adiabatic index is analyzed. The pressure of the star, at the beginning of the collapse, is isotropic but due to the presence of the shear the pressure becomes more and more anisotropic. The black hole is never formed because the apparent horizon formation condition is never satisfied, in contrast of the previous model where a black hole is formed. An observer at infinity sees a radial point source radiating exponentially until reaches the time of maximum luminosity and suddenly the star turns off. In contrast of the former model where the luminosity also increases exponentially, reaching a maximum and after it decreases until the formation of the black hole. The effective adiabatic index is always positive without any discontinuity in contrast of the former model where there is a discontinuity around the time of maximum luminosity. The collapse is about three thousand times slower than in the case where the energy density is initially homogeneous. © 2010 Springer Science+Business Media, LLC.

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