Stable Gravastars of Anisotropic Dark Energy

Dynamical models of prototype gravastars made of phantom energy are constructed, in which an infinitely thin spherical shell of a perfect fluid with the equation of state $p = (1-\gamma)\sigma$ divides the whole spacetime into two regions, the internal region filled with a dark energy (or phantom) fluid, and the external Schwarzschild region. It is found that in some cases the models represent the "bounded excursion" stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes or normal stars. In the phase space, the region for the "bounded excursion" gravastars is very small in comparison to that of black holes, but not empty, as found in our previous papers. Therefore, although the existence of gravastars can not be completely excluded from current analysis, the opposite is not possible either, that is, even if gravastars exist, they do not exclude the existence of black holes.Comment: 35 pages, 43 figures, added some clarifying texts and corrected some typos, accepted for publication in JCA

The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory

We give a new theoretical basis for examination of the presence of the Kerr black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of different astrophysical objects around which astrophysical jets are typically formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei (AGN), etc. Our method is based on the study of the exact solutions of the Teukolsky master equation for electromagnetic perturbations of the Kerr metric. By imposing original boundary conditions on the solutions so that they describe a collimated electromagnetic outflow, we obtain the spectra of possible {\em primary jets} of radiation, introduced here for the first time. The theoretical spectra of primary electromagnetic jets are calculated numerically. Our main result is a detailed description of the qualitative change of the behavior of primary electromagnetic jet frequencies under the transition from the KBH to the KNS, considered here as a bifurcation of the Kerr metric. We show that quite surprisingly the novel spectra describe linearly stable primary electromagnetic jets from both the KBH and the KNS. Numerical investigation of the dependence of these primary jet spectra on the rotation of the Kerr metric is presented and discussed.Comment: 18 pages, 35 figures, LaTeX file. Final version. Accepted for publication in Astrophysics and Space Science. Amendments. Typos corrected. Novel notion -"primary jet" is introduced. New references and comments adde

Anisotropic dark energy stars

A model of compact object coupled to inhomogeneous anisotropic dark energy is studied. It is assumed a variable dark energy that suffers a phase transition at a critical density. The anisotropic Lambda-Tolman-Oppenheimer-Volkoff equations are integrated to know the structure of these objects. The anisotropy is concentrated on a thin shell where the phase transition takes place, while the rest of the star remains isotropic. The family of solutions obtained depends on the coupling parameter between the dark energy and the fermion matter. The solutions share several features in common with the gravastar model. There is a critical coupling parameter that gives non-singular black hole solutions. The mass-radius relations are studied as well as the internal structure of the compact objects. The hydrodynamic stability of the models is analyzed using a standard test from the mass-radius relation. For each permissible value of the coupling parameter there is a maximum mass, so the existence of black holes is unavoidable within this model.Comment: 12 pages, 6 figures, final manuscript, Accepted for publication in Astrophysics & Space Scienc

Star Models with Dark Energy

We have constructed star models consisting of four parts: (i) a homogeneous inner core with anisotropic pressure (ii) an infinitesimal thin shell separating the core and the envelope; (iii) an envelope of inhomogeneous density and isotropic pressure; (iv) an infinitesimal thin shell matching the envelope boundary and the exterior Schwarzschild spacetime. We have analyzed all the energy conditions for the core, envelope and the two thin shells. We have found that, in order to have static solutions, at least one of the regions must be constituted by dark energy. The results show that there is no physical reason to have a superior limit for the mass of these objects but for the ratio of mass and radius.Comment: 20 pages, 1 figure, references and some comments added, typos corrected, in press GR

Status Report Of The Schenberg Gravitational Wave Antenna

Here we present a status report of the Schenberg antenna. In the past three years it has gone to a radical upgrading operation, in which we have been installing a 1K pot dilution refrigerator, cabling and amplifiers for nine transducer circuits, designing a new suspension and vibration isolation system for the microstrip antennas, and developing a full set of new transducers, microstrip antennas, and oscillators. We are also studying an innovative approach, which could transform Schenberg into a broadband gravitational wave detector.3631Aguiar, O.D., (2002) Class. Quantum Grav., 19, p. 1949Aguiar, O.D., (2004) Class. Quantum Grav., 21, pp. S457Aguiar, O.D., (2005) Class. Quantum Grav., 22, pp. S209Aguiar, O.D., (2006) Class. Quantum Grav., 23, pp. S239Aguiar, O.D., (2008) Class. Quantum Grav., 25, p. 114042Costa, C.A., (2008) Class. Quantum Grav., 25, p. 184002Johnson, W.W., Merkowitz, S.M., (1993) Phys. Rev. Lett., 70, p. 2367Coccia, E., Lobo, J.A., Ortega, J.A., (1995) Phys. Rev. D, 52, p. 3735Thorne, K.S., (1978) Phys. Rev. Lett., 40, p. 667Tobar, M.E., Ivanov, E.N., Blair, D.G., (2000) Gen. Rel. Grav., 32, p. 1799De Waard, (2005) Class. Quantum Grav., 22, pp. S215Vinet, J.-Y., (2010) Research in Astron Astrophys., 10, p. 956Costa, C.A., Aguiar, O.D., Magalhães, N.S., (2004) Class. Quantum Grav., 21, pp. S827Forward, R.L., (1971) Gen. Rel. Grav., 2, p. 149Eardley, D.M., Lee, D.L., Lightman, A.P., Wagoner, R.V., Will, C.M., (1973) Phys. Rev. Lett., 30, p. 884Bianchi, M., Coccia, E., Colacino, C.N., Fafone, V., Fucito, F., (1996) Class. Quantum Grav., 13, p. 2865Andrade, L.A., (2009) Microwave and Optical Tech. Lett., 51, p. 1120Furtado, S.R., (2012), in preparationIvanov, E.N., Hartnett, J.G., Tobar, M.E., (2000) IEEE Trans. Ultrason., Ferroelect., Freq. Contr., 47, p. 1526Pimentel, G.L., (2008) J. Phys. Conf. Series, 122, p. 012028Aguiar, (2009) Int. J. Modern Phys. D, 18, p. 2317Furtado, S.R., (2009), Ph.D. Thesis at INPE, not publishedBraginsky, V.B., Vorontsov, Y.I., Thorne, K.S., (1980) Science, 209, p. 547Thorne, K.S., The Quantum Limit for Gravitational-Wave Detectors and Methods of Circumventing It (1979) Sources of Gravitational Waves, p. 49. , ed. L L Smarr, Cambridge University Press, Cambridge, US

Status Report of the Schenberg Gravitational Wave Antenna

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