This dissertation investigates the signatures of electromagnetic radiation that may accompany two specific sources of gravitational radiation: the inspiral and merger of massive black hole binaries (MBHBs) in galactic nuclei, and the coalescence of black hole neutron star (BHNS) pairs. Part I considers the interaction of MBHBs, at sub-pc separations, with a circumbinary gas disk. Accretion rates onto the MBHB are calculated from two-dimensional hydrodynamical simulations as a function of the relative masses of the black holes. The results are applied to interpretation of the recent, sub-pc separation MBHB candidate in the nucleus of the periodically variable Quasar PG 1302-102. We advance an interpretation of the variability observed in PG 1302-102 as being caused by Doppler-boosted emission sourced by the orbital velocity of the smaller black hole in a MBHB with disparate relative masses. Part II considers BHNS binaries in which the black hole is large enough to swallow the neutron star whole before it is disrupted. As the pair nears merger, orbital motion of the black hole through the magnetosphere of the neutron star generates an electromotive force, a black-hole-battery, which, for the strongest neutron star magnetic field strengths, could power luminosities large enough to make the merging pair observable out to cosmic distances. Relativistic solutions for vacuum fields of a magnetic dipole near a horizon are given, and a mechanism for harnessing the power of the black-hole-battery is put forth in the form of a fireball emitting in hard X-rays to to gamma-rays.

Este trabalho visa o estudo das perturbações de sistemas gravitacionais altamente compactos, como buracos negros e estrelas de nêutrons e de quarks. As perturbações em questão podem ser de diversas naturezas (escalar, eletromagnética ou gravitacional), sendo que detivemo-nos mais atentamente naquelas de natureza gravitacional, pois estas têm despertado mais interesse por serem astronomicamente mais fáceis de detectar. Além de estudarmos tais perturbações, procedemos a uma comparação dos resultados para buracos negros, estrelas de nêutrons e de quarks. Tal comparação justifica-se pelo fato de que a confrontação de previsões teóricas com resultados experimentais pode ajudar-nos a identificar objetos astronômicos de interesse, distingüi-los e, no caso de estrelas, aprender algo sobre sua estrutura interna, particularmente sobre a equação de estado (EDE) do fluido estelar. No que se segue, dividimos o trabalho em sete partes. Em primeiro lugar, damos uma introdução bastante sucinta ao mesmo (Capítulo 1). Depois, falamos sobre a física de estrelas de nêutrons e de quarks (Capítulo 2). A seguir, fazemos um estudo comparativo dos dois tipos de estrelas (Capítulo 3). Mais adiante, discutimos as perturbações de diversos tipos, além de definir os MQNs (Modos Quasi-Normais) de buracos negros de Schwarzschild (Capítulo 4). Prosseguimos a discussão com a métrica de Reissner-Nordström-de Sitter (Capítulo 5) e introduzimos, na seqüência, os MQNs estelares, de forma muito breve (Capítulo 6). Por fim, apresentamos nossas conclusões (Capítulo 7). A parte inédita deste trabalho está concentrada nos capítulos 5 e 6, os quatro anteriores servindo de preparativo e de base comparativa para estes dois. / This work aims the detailed study of the perturbations of highly compact gravitational systems, such as black holes and both neutron and quark stars. Such perturbations may have several different characters, such as scalar and electromagnetic fields as well as gravitational (either axial or polar) disturbances. We have focused more closely on the latter kind of perturbation, since they offer better possibilities of detection in the near future, in the form of gravitational waves. Besides studying the aforementioned perturbations, we have proceeded to a comparison between black holes and neutron and quark stars , when it comes to the outcomes of the perturbations, usually called QNMs (quasi-normal modes). Such a comparison is actually in order, since a direct comparison of theoretical and observational data may help us identify astronomical objects and, in the case of compact stars, may provide valuable insights into these stars' inner structure, particularly when it comes to their equation of state (EOS). In what follows, we have subdivided this work in seven parts. We begin with a brief introduction (Chapter 1), then proceed to a description of the physics of both neutron and quark stars (Chapter 2) and, in the sequence, to a comparative study of both kinds of star (Chapter 3). Subsequently, we develop the perturbation theory of the Schwarzschild black holes, discussing their QNMs (Chapter 4) and doing the same, later, for a more general Reissner-Nordström-de Sitter geometry (chapter 5). After that, we provide a very brief introduction to the stellar MQNs (Chapter 6). Finally, we present our conclusions (Chapter 7). The chapters 5 and 6 carry the inedit part of this work, and the chapters from 1 to 4 pave the way and provide a comparative basis for them.

No contexto da teoria da relatividade geral de Einstein, se estudam espaço-tempos dinâmicos do tipo buraco negro em um ambiente cosmológico, em particular, uma generalização de massa variável do espaço-tempo de McVittie. São apresentados alguns espaço-tempos resultantes de limites da solução de McVittie generalizada. Se discutem as definições padrão de buraco negro e horizonte de eventos assim como as dificuldades de aplicá-las em situações dinâmicas, outras definições para horizontes são exploradas. É usado o conceito de horizonte aparente para localizar buracos negros e horizontes cosmológicos. Soluções para a busca dos horizontes aparentes são encontradas nas geometrias de Schwarzschild-de Sitter, McVittie e McVittie generalizado. / Black hole-like spacetimes in a cosmological background are studied within the Einsteins general relativity theory framework, in particular a mass varying generalization of the McVitties spacetime. We exhibit some of the resulting spacetimes as limit cases of the generalized McVittie solution. We discuss the standard definition of black hole and event horizon, and we address the difficulties in aplying it in dynamical situations, another definitions for horizons are explored. The apparent horizon concept is used to locate black holes and cosmological horizons. Solutions for apparent horizons in Schwarzschild-de Sitter, McVittie, and generalized McVittie geometries are shown.

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Made available in DSpace on 2016-12-23T14:20:02Z (GMT). No. of bitstreams: 1 Junior Diniz Toniato.pdf: 412954 bytes, checksum: 2559260e7dcddc93c1ce6baff90a288d (MD5) Previous issue date: 2010-07-29 / There isn t experimental evidences that can validate the results of black holes termodynamics. This because the radiation emitted by the black hole, predicted by theory, it is almost impossible to be detected due to its low value of magnitude. In the search for clues that could validate the existence of this radiation, the study of analog models to those objetcs has grown considerably in recent decades. They allow the idealization of experiments in labs that would be extremely complicate to be done directly with the gravitational systems. A fluid in moviment can act on the sound the same way that curved space-time can influence on light trajectory in the general relativity. So, one can describe the propagation these sound waves through an effective metric, under wich they will follow null geodesics. This thesis makes a review of these studies focusing in an analogy to Schwarzschild black hole using an acoustic system, showing its advantages and limitations when applied in the study of Hawking s theory / Ainda não há uma comprovação experimental que possa validar os resultados obtidos da termodinâmica de buracos negros. Isso porque a radiação emitida pelo buraco negro, prevista pela teoria, é praticamente impossível de ser detectada devido ao baixo valor de sua ordem de grandeza. Na busca por indícios que possam validar a existência dessa radiação, o estudo de modelos análogos a esses objetos tem crescido consideravelmente nas últimas décadas. Eles permitem a idealização de experimentos em laboratórios que seriam impossíveis de serem realizados diretamente nos sistemas gravitacionais. Um fluido em movimento pode agir sobre o som da mesma forma que os espaçotempos curvos podem influenciar na trajetória da luz na relatividade geral. Com isso, pode-se descrever a propagação dessas ondas sonoras através de uma métrica efetiva, sob a qual elas seguirão geodésicas nulas. Esta dissertação faz uma revisão destes estudos concentrando-se em uma analogia acústica para um buraco negro de Schwarzschild, demonstrando suas vantagens e limitações quando aplicada para o estudo da teoria de Hawking

In this thesis we study exact general relativistic space-times generated by a black hole and an additional source of gravity, while restricting to two classes of static and axially symmetric solutions: the Majumdar-Papapetrou solution for a couple (in general, a multiple system) of extremally charged black holes and the "superposition" of a Schwarzschild black hole with the Bach-Weyl thin ring. We follow the effect of the additional source on the geometry of black-hole space-time on the behaviour of important invariants, in particular of the simplest scalars obtained from the Riemann and possibly also Ricci tensor. We have plotted the invariants both outside and inside the black hole; in the case of a Schwarzschild black hole with ring, we found, to this end, an extension of the metric below the horizon. It turns out that the external source may affect the geometry inside the black hole considerably, even in the vicinity of singularity, although the singularity itself remains point-like in both solutions studied here.

General relativity, one of the pillars of our understanding of the universe, has been a remarkably successful theory. It has stood the test of time for more than 100 years and has passed all experimental tests so far. Most recently, the LIGO collaboration made the first-ever direct detection of gravitational waves, confirming a long-standing prediction of general relativity. Despite this, several fundamental mathematical questions remain unanswered, many of which relate to the global existence and the stability of solutions to Einstein's equations. This thesis presents our efforts to use numerical relativity to investigate some of these questions. We present a complete picture of the end points of black ring instabilities in five dimensions. Fat rings collapse to Myers-Perry black holes. For intermediate rings, we discover a previously unknown instability that stretches the ring without changing its thickness and causes it to collapse to a Myers-Perry black hole. Most importantly, however, we find that for very thin rings, the Gregory-Laflamme instability dominates and causes the ring to break. This provides the first concrete evidence that in higher dimensions, the weak cosmic censorship conjecture may be violated even in asymptotically flat spacetimes. For Myers-Perry black holes, we investigate instabilities in five and six dimensions. In six dimensions, we demonstrate that both axisymmetric and non-axisymmetric instabilities can cause the black hole to pinch off, and we study the approach to the naked singularity in detail. Another question that has attracted intense interest recently is the instability of anti-de Sitter space. In this thesis, we explore how breaking spherical symmetry in gravitational collapse in anti-de Sitter space affects black hole formation. These findings were made possible by our new open source general relativity code, GRChombo, whose adaptive mesh capabilities allow accurate simulations of phenomena in which new length scales are produced dynamically. In this thesis, we describe GRChombo in detail, and analyse its performance on the latest supercomputers. Furthermore, we outline numerical advances that were necessary for simulating higher dimensional black holes stably and efficiently.

Les cycles d’hysteresis des binaires X lors de leurs sursauts restent inexpliqués a ce jour. Dans ce travail, nous avons développé les idées du paradigme propose par Ferreira et al. (2006), ou la matière dans le disque accrète de deux manières différentes. Dans le mode standard (SAD, Shakura et Sunyaev 1973), le couple turbulent transporte le moment cinétique radialement vers l’extérieur du disque. Dans le mode éjectant (JED, Ferreira et Pelletier 1995), le disque magnetise produit des jets qui emporte la matière, l’énergie et le moment angulaire verticalement. Dans ce cadre, la transition entre les deux modes est liée a la distribution de champ magnétique dans le disque, une inconnue. Pendant cette thèse, j’ai développé un code capable de résoudre a chaque rayon dans un disque l’équilibre thermique a deux températures pour de multiples jeu de paramètres. Ce code utilise Belm (Belmont et al. 2008 ; Belmont 2009) pour traiter le refroidissement radiatif et créer les spectres de manière auto-cohérente. Les processus de chauffage sont analytiques, ainsi que les processus d’advection, qui sont calcules de l’interieur vers l’exterieur.Grace a ce code, nous avons pu montrer que des solutions de JED reproduisaient très bien les états hard jusqu’à 0.5 luminosités d’Eddington (Marcel et al. 2018a). Il a aussi été démontré que le JED subit un cycle d’hysteresis. En revanche, la luminosité de ce cycle est bien trop faible et la présence inévitable de jets dans la configuration nous pousse a l’utilisation d’un SAD pour la reproduction d’états soft.Fort de ces résultats, j’ai adapte le code a la résolution de configuration de disque hybride, compose d’un JED interne et d’un SAD externe, séparé en un rayon de transition rJ. En jouant sur ce paramètre rJ et sur le taux d’accrétion mdot, nous avons pu montrer que les observations X de cycles typiques pouvaient être pavée. Après des calculs similaires a Heinz et Sunyaev (2003), nous pouvons estimer quel est le flux radio associe a chaque jeu de paramètres. Cela nous a permis de montrer 2 choses. (1) tous les flux radios sont reproductibles a l’aide d’un seul facteur de normalisation commun. (2) le flux radio et la forme du spectre en rayons X sont cohérents : les jeux de paramètres qui reproduisent le mieux chaque forme spectral sont associes aux bon flux radios. Afin d’illustrer ce résultat, 5 états canoniques de l’évolution de GX 339-4 ont ete reproduits : forme spectrale en X et flux radios (Marcel et al. 2018b). Pour finir, en utilisant une simple procédure d’ajustement sur la forme spectrale en X, le cycle de 2010-2011 de GX 339-4 a pu être reproduit. De manière bluffante, les évolutions de rJ et mdot semblent être en accord avec les prédictions théoriques (Esin et al. 1997). De plus, les estimations de flux radio étant cohérentes avec les observations, nous avons décidé de les ajouter directement dans la procédure d’ajustement. L’ajout de cette composante a permis une excellente reproduction simultanée de la radio et des spectres X de manière. C’est, a notre connaissance, la première fois que les phénomènes d’accrétion et d’éjection sont utilisés simultanément. Ces résultats, ainsi que les discussions et implications seront bientôt soumis. / The hysteresis behavior of X-ray binaries during their outbursts remains a mystery. In this work, we developed the paradigm proposed in Ferreira et al. (2006) where the disk material accretes in two possible, mutually exclusive, ways. In the standard accretion disk (SAD, Shakura et Sunyaev 1973) mode, the dominant local torque is due to MHD turbulence that transports radially the disk angular momentum. In the jet-emitting disk (JED, Ferreira et Pelletier 1995) mode, magnetically-driven jets carry away mass, energy and all the angular momentum from the disk. Within our framework, the transition from one mode to another is related to the magnetic field distribution, an unknown yet.In this thesis, I have developped a two-temperature plasma code able to compute the thermal balance at each radius for a large ensemble of disk parameters, as well as the self- consistent global emitted spectrum. The radiative cooling term and related spectrum (comptonized bremsstrahlung and synchrotron emission) are obtained using the Belm code (Belmont et al. 2008 ; Belmont 2009). Heating processes are analytical and due only to accretion, while advection is properly taken into account, carrying outside-in the memory of the outer thermal states.Using this code, we have shown that a JED extending along the entire disk nicely repro- duces hard states up to 0.5 Eddington luminosities (Marcel et al. 2018a). It was also shown that JEDs produce a natural hysteresis cycle. However, the global luminosity of the cycle is insufficient and the inevitable presence of jets in JEDs advocates for an inner SAD configuration in soft states.Based on these results, the code was enhanced to solve hybrid configurations with an internal JED and an external SAD, separated by a given transition radius rJ. Playing on both rJ and the accretion rate mdot, we have shown that X-ray observations of typical cycles can be completely covered. Using a simple synchrotron model similar to that of Heinz et Sunyaev (2003), the radio flux produced by the jets can be estimated, showing two important features. First, all radio observations can be covered by our model. Second, the radio flux and X- ray spectral coverages are consistents : parameter sets that reproduce best each spectral state also account for a consistent associated radio flux. For illustration, 5 canonical states from GX 339-4 have been reproduced in X-ray spectral shape and associated radio fluxes (Marcel et al. 2018b).Finaly, using a simple fitting procedure on X-ray spectral shape, the 2010-2011 cycle from GX 339-4 has been reproduced. Strikingly, the co-evolution of rJ and mdot seems to be in adequacy with initial theoretical expectations (Esin et al. 1997). Moreover, the estimated radio flux evolution being close to observations, we decided to use those within the fitting procedure. Adding radio fluxes constraints in the procedure allowed us to reproduce both the associated X-ray spectral shape and radio fluxes with excellent agreement. This is, to our knowledge, the first time that such an accretion-ejection cycle is reproduced. Those results, as well as discussions and implications will be soon submitted.

Esta tese é um estudo de estabilidade de modos quasinormais em um sistema que apresenta uma mudança de estabilidade ao variar continuamente os parâmetros físicos de um buraco negro. A mudança de estabilidade encontrada possui interpretações na correspondência AdS/CFT. A ferramenta principal utilizada neste trabalho para o cálculo de modos quasinormais foram métodos numéricos que podem ser utilizados em inúmeros trabalhos desta área de pesquisa, especialmente por não dependerem de suposições de simetria ou de comportamento conveniente do sistema físico. / This thesis is a study of stability of quasinormal modes in a system featuring a stability change if one continuously varies the physical parameters of a black hole. The stability change thus found has some possible interpretations in the AdS/CFT correspondence. The main tool used in this study for calculating quasinormal modes are numerical methods that can be used in numerous works in this area of research, especially because they do not depend on assumptions of symmetry or any convenient behavior of the physical system.

Neste trabalho faremos uma investigação no campo das perturbações gravitacionais e propagação de ondas em geometrias de buracos negros com campos elétricos ou magnéticos. Usando uma geometria tipo Ernst-Melvin de um buraco negro massivo em um Universo com campo magnético no eixo z, calculamos os modos quasi-normais de propagação de um campo escalar, demonstrando que este se comporta como um campo escalar com massa 2|m|B em uma geometria de Schwarzschild, para pequenos valores do campo magnético B (correspondendo m ao número azimutal do esférico harmônico). Ainda com esta geometria, calculamos a contribuição de ondas escalares para a entropia do buraco negro em termos dos cut offs ultravioleta e infravermelho. Com uma solução do tipo Reissner-Nordström em 4 dimensões, investigamos as possíveis correspondências entre os modos quasinormais e as propriedades termodinâmicas deste buraco negro, atestando o resultado de que a conjectura Hod modificada por Maggiore é válida em tal solução. Também, com uma geometria de Reissner-Nordström-de Sitter D-dimensional, obtivemos os modos quasi-normais de vibração para dois potenciais diferentes, estabelecendo a ausência de modos instáveis para uma grande gama de parâmetros deste buraco negro. / In this work we make an incursion into the branch of gravitational perturbations and field propagation around known-geometries of black holes with electromagnetic fields. Using an Ernst-Melvin type of geometry in a massive black hole immersed on a magnetic Universe, we calculate the quasi-normal modes of the propagating field, showing the equivalence of this problem with that of a massive scalar field (for which the mass is 2|m|B, m being the azhimutal number, and B the magnetic field) propagating around a Schwarzschild geometry. We also compute the contribution of the scalar field to the entropy of the black hole in terms of the infrared and ultraviolet cut offs. Using a Reissner-Nordstr¨om-like solution in 4 dimensions, we investigate the possible correspondence between quasi-normal modes and the thermodynamical properties of this black hole, atesting the validity of the modified Hod conjecture as proposed by Maggiore. Finally, for a Reissner-Nordstr¨om-de Sitter D-dimensional solution, we obtain the quasi-normal modes for two diferent potentials, establishing the absence of unstable modes for a large range of values for the black hole parameters.