Black Hole
Mostrando 13-24 de 46 artigos, teses e dissertações.
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13. MODOS QUASE-NORMAIS E A CORRESPONDÊNCIA ADS/CFT / QUASINORMAL MODES AND THE ADS/CFT CORRESPONDENCE
The electromagnetic and gravitational quasinormal mode spectra of plane-symmetric anti-de Sitter black holes are investigated in the present work. According to the AdS/CFT correspondence, the black hole quasinormal frequencies correspond to the poles of R-current and stress-energy tensor correlation functions in the holographically dual field theory: the N =
Publicado em: 2008
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14. Buracos negros em universos brana com constante cosmológica / Black holes in brane worlds with cosmological constant
We found classes of static and spherically symmetric black hole solutions on the brane for a vacuum configuration, non-null cosmological constant, embedded into a 5-dimensional asymptotically anti-de Sitter bulk. In the asymptotically de Sitter case, the only solution obtained was the extreme Schwarzschild-de Sitter geometry. In the asymptotically anti-de Si
Publicado em: 2008
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15. Seção de choque de absorção de buracos negros de Schwarzschild e de buracos acústicos canônicos / Section of shock of absorption of black holes of Schwarzschild and of canonical acoustic holes
In this dissertation we compute the absorption cross section of Schwarzschild black holes for the massless scalar and electromagnetic fields. We also compute the absorption cross section of canonical acoustic holes for sound waves. We use a numerical method to obtain the results in arbitrary frequencies. We also obtain analytic expressions for the low- and h
Publicado em: 2008
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16. Fundo estocástico de ondas gravitacionais gerados por buracos negros pré-galáctiocs / Stochastic Background of Gravitational Waves Generated By pre-galactic Black Hole Formation
Observation of the Cosmic Microwave Background Radiation (CMB) provide us with a clear information about the status of matter and radiation at the decoupling era like a snapshot of the Universe 300.000 years after the Big-Bang. Nowadays, through observations of the cosmic structure, we can build-up the history of the Universe from one billion years after the
Publicado em: 2008
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17. Fundo estocástico de ondas gravitacionais gerados por buracos negros pré-galáctiocs / Stochastic Background of Gravitational Waves Generated By pre-galactic Black Hole Formation
A observação da radiação cósmica de fundo em microondas nos fornece informação sobre o momento em que matéria e radiação desacoplaram, como uma fotografia produzida 300.000 anos após o Big-Bang. Hoje, através da observação de estruturas e objetos cósmicos, podemos avaliar o comportamento do Universo em tempos mais recentes (em torno de um bilh
Publicado em: 2008
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18. Born-Infeld corrections to the entropy function of heterotic black holes
We use the black hole entropy function to study the effect of Born-Infeld terms on the entropy of extremal black holes in heterotic string theory in four dimensions. We find that after adding a set of higher curvature terms to the effective action, attractor mechanism works and Born-Infeld terms contribute to the stretching of near horizon geometry. In the a
Brazilian Journal of Physics. Publicado em: 2007-06
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19. An extensive search for overtones in Schwarzschild black holes
In this paper we show that with standard numerical methods it is possible to obtain highly precise results for quasi normal modes (QNMs). In particular, secondary modes are obtained by numerical integration done in the well-known null grid. We have compared such numerical results to the also well-known 6th-order WKB method and have found a striking degree of
Brazilian Journal of Physics. Publicado em: 2007-06
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20. Estabilidade de curvas tipo-tempo fechadas em variedades lorentzianas / Stability of closed timelike curves in Lorentzian manifolds
Several solutions of Einstein?s field equations admit closed timelike curves (CTCs). We study the linear stability of this kind of curve. We analyze the CTCs in Gödel universe and we find that these curves are stable. The same occurs with the CTCs of a particular case of Gödel-type metric with flat background and with CTCs of a model that contains a single
Publicado em: 2007
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21. Scalar perturbation in a black hole localized on a brane
In this work we study a scalar perturbation in a brane black hole with Schwarzschild behavior, localized on the brane. This black hole solution was derived by Casadio, Fabbri and Mazzacurati with the metric satisfying the condition R = 0, where R is the four-dimensional scalar curvature.
Brazilian Journal of Physics. Publicado em: 2005-12
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22. Electric charge rotating around a black hole
We consider an electric charge rotating around a Schwarzschild black hole. We compute, using quantum field theory in curved spacetime at the tree level, the power emitted by the rotating charge minimally coupled to the Maxwell field. We also compute how much of the radiation emitted by the swirling charge is absorbed by the black hole.
Brazilian Journal of Physics. Publicado em: 2005-12
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23. High overtones of dirac perturbations of a Schwarzschild black hole and the area spectrum of quantum black holes
We find high overtones of the Dirac quasi-normal (QN) spectrum of a Schwarzschild black hole (Sbh), by Leaver's method. At high overtones, the spacing of the imaginary part of the QN spectrum is equidistant (Im omegan+1- Im omegan = i/8M , where M is the black hole mass). This can also be analytically obtained by means of a Born approximation. At high overto
Brazilian Journal of Physics. Publicado em: 2005-12
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24. Influence of the black hole rotation on accretion discs and jets in active galaxies: the case of NGC 1068
Although we do not observe directly black holes in the Universe, their presence has been inferred in several astrophysical systems, from galactic to extragalactic scales. In this work, we will restrict our focus in the possible signatures of the presence of Kerr black holes in active galactic nuclei, one of the most powerful sources in the Universe. Particul
Brazilian Journal of Physics. Publicado em: 2005-12