Academic literature on the topic 'Black hole - hydrodynamics'

Massive stars in a certain mass range (20 – 40M⊙) may form low mass black holes after supernova explosions. In such massive stars, fall back of ~ 0.1M⊙ materials onto a black hole is expected due to a deep gravitational potential or a reverse shock propagating back from the outer composition interface. We study hydrodynamical disk accretion onto a new-born low mass black hole in a supernova using the SPH (Smoothed Particle Hydrodynamics) method.

ABSTRACT We study the evolution of accretion disk around a supermassive binary black hole with equal mass using non-relativistic hydrodynamical simulations performed with FARGO3D. Compared with previous studies with the Newtonian hydrodynamics, here, we adopt the post-Newtonian (PN) hydrodynamics using the near zone metric of the binary black hole. In contrast to the Newtonian investigation, we find that there is a dramatic difference in the PN regime, gap formed by the circumbinary accretion disk around the binary with equal mass is wider with the PN hydrodynamics than that with the Newtonian hydrodynamics and is independent of disk viscosity given that hydrodynamical simulations are run for about the same factor times the viscous timescale associated with different viscosities. This may present unique observable signatures of the continuum emission in such binary-disk system.

Newtonian fluid dynamics allows the construction of acoustic metrics from which black hole configurations can be studied. However, relativistic pressure effects are neglected within Newtonian theory. We study acoustic black holes in the framework of neo-Newtonian hydrodynamics, which is designed to take into account relativistic inertial effects of the pressure p. Within this new hydrodynamical context we show how p can influence the formation of the acoustic horizons.

We investigate the relations between black hole thermodynamics and holographic transport coefficients in this paper. The formulae for DC conductivity and diffusion coefficient are verified for electrically single-charged black holes. We examine the correctness of the proposed expressions by taking charged dilatonic and single-charged STU black holes as two concrete examples, and compute the flows of conductivity and diffusion coefficient by solving the linear order perturbation equations. We then check the consistence by evaluating the Brown-York tensor at a finite radial position. Finally, we find that the retarded Green functions for the shear modes can be expressed easily in terms of black hole thermodynamic quantities and transport coefficients.

In the presence of a rotating Kerr black hole, we investigate hydrodynamics of the massive particles and massless photons to construct relations among number density, pressure and internal energy density of the massive particles and photons around the rotating Kerr black hole and to study an accretion onto the black hole. On equatorial plane of the Kerr black hole, we investigate the bound orbits of the massive particles and photons around the black hole to produce their radial, azimuthal and precession frequencies. With these frequencies, we study the black holes GRO J1655-40 and 4U 1543-47 to explicitly obtain the radial, azimuthal and precession frequencies of the massive particles in the flow of perfect fluid. We next consider the massive particles in the stable circular orbit of radius of 1.0 ly around the supernovas SN 1979C, SN 1987A and SN 2213-1745 in the Kerr curved spacetime, and around the potential supermassive Schwarzschild black holes M87, NGC 3115, NGC 4594, NGC 3377, NGC 4258, M31, M32 and Galatic center, to estimate their radial and azimuthal frequencies, which are shown to be the same results as those in no precession motion. The photon unstable orbit is also discussed in terms of the impact parameter of the photon trajectory. Finally, on the equatorial plane of the Kerr black hole, we construct the global flat embedding structures possessing (9 + 3) dimensionalities outside and inside the event horizon of the rotating Kerr black hole. Moreover, on the plane, we investigate the warp products of the Kerr spacetime.

AbstractThe “central engine” of quasars and active galactic nuclei Is most likely powered by accretion into a supermassive black hole. A menagerie of steady state accretion flows have been developed, and these are briefly reviewed. Several examples from recent numerical calculations of axisymmetric accretion flows provide disk formation scenarios from which one can calculate plasma densities, and other values of interest for a range of accretion rates and black hole masses. These results can be compared with the well studied, but physically unrealistic case of radial accretion. Although a reasonable conceptual picture of the central engine has been developed, considerable work remains to be done.

A method for the phenomenological description of particle production is proposed. Correspondingly modified equations of motion and energy-momentum tensor are obtained. In order to illustrate this method we reconsider from the new point of view of (i) the C-field Hoyle-Narlikar cosmology, (ii) the influence of the particle production process on metric inside the event horizon of a charged black hole and (iii) a nonsingular cosmological model.

In questa tesi ci si propone di analizzare le implicazioni fisiche della geometria dello spazio ambiente nel contesto dei condensati di Bose-Einstein (BEC) e le possibili applicazioni nell’ambito dei modelli analogici della cosmologia dei buchi neri. A tal fine si deriva la formulazione idrodinamica dell'equazione di Gross-Pitaevskii (GPE) nel caso di una generica varietà Riemanniana e si osserva la comparsa di una nuova forza, che dipende essenzialmente da due parametri: la geometria della varietà e le derivate prime del profilo di densità. Si studiano le condizioni stazionarie in relazione alla presenza di varietà a curvatura scalare negativa. Analizzando tali varietà si stabilisce una relazione esplicita tra le superfici a curvatura negativa e l'equazione di seno-Gordon, che risulta un'approssimazione della GPE nel caso di accoppiamento di fasi. Assumendo condizioni stazionarie, si ottiene un nuovo tipo di equazioni di Einstein e si è spinti a ricercare altri legami tra le equazioni che governano i condensati e la cosmologia. A tal fine si considerano i BEC relativistici, che vengono utilizzati nello studio del comportamento dell'universo primordiale e della sua espansione. Facendo uso delle conoscenze ottenute nel caso di varietà Riemanniane generiche, otteniamo nuove equazioni di Einstein nel caso multi-dimensionale. Successivamente, si considerano i modelli analogici utilizzati per lo studio della formazione di buchi neri e per il calcolo della radiazione di Hawking. Attraverso un processo di linearizzazione si nota come sia possibile far emergere una metrica acustica Lorentziana che governi il moto delle fluttuazioni della fase; a questo scopo si considera il caso di un vortice dritto che presenta un profilo di densità in cui le derivate prime assumono un valore massimo all’interno del tubo vorticoso e la geometria dello spazio ambiente diventa rilevante. In questa situazione si scopre che è effettivamente possibile far emergere una metrica Lorentziana, e si propongono alcune approssimazioni utili per la sua determinazione esplicita. Infine, vengono presentate alcune osservazioni conclusive su possibili direzioni di ricerca future, quali lo studio dell'evoluzione delle superfici isofase in casi relativistici e lo studio dei condensati sottoposti a torsione.
In this thesis we analyze the physical implications of the geometry of the ambient space in the context of Bose-Einstein condensates (BECs) and possible applications to the field of analogue models in the cosmology of black holes. To this end we derive the hydrodynamic formulation of the Gross-Pitaevskii equation (GPE) in the case of a generic Riemannian manifold. We observe the appearance of a new force, which essentially depends on two parameters: the geometry of the manifold and the first derivatives of the density profile. The stationary conditions are studied in relation to the presence of manifolds with negative scalar curvature. By analyzing these manifolds, an explicit relationship is established between the negatively curved surfaces and the sine-Gordon equation, which results in an approximation of the GPE in the presence of phase coupling. By assuming stationary conditions, we obtain a new type of Einstein field equations and we look for other possible connections between the equations governing condensates and cosmology. For this purpose, we consider relativistic BECs, that are used in the study of the early universe and its expansion, and we obtain Einstein equation in the multi-dimensional case. Then we consider the analogue models used for the study of the formation of black holes and for the calculation of Hawking radiation. Through a linearization process it is possible to derive a Lorentzian acoustic metric for the phase fluctuations; for this purpose, we consider the case of a straight vortex defect with a density profile where the first derivatives have maximum value inside the vortex tube and the geometry of the ambient space becomes relevant. In this situation it turns out that it is possible to determine a Lorentzian metric, and some useful approximations are proposed for its explicit computation. Finally, some concluding remarks are presented on possible future research directions, given by the study of the evolution of isophase surfaces in relativistic cases, and the study of condensates subject to twist.

A Super Massive Black Hole (SMBH) with a mass of 4 106M⊙ lurks in the center of the Milky Way known as Sagittarius A* (Sgr A*). Its presence affects both the Galactic Center (GC) interstellar gas, of which the central molecular zone is an example, as well as the stellar system in which it resides. A direct effect of the presence of Sgr A* is the capture of objects, in particular stars, leaving a trace of of X-ray (soft and hard) and gamma-ray emissions. A secondary effect is the origin and powering of the Fermi Bubbles, large superbubbles extending 8 kpc above and below the GC. Their energetic content (1055 erg) points towards an origin due to the tidal disruption of stars that end up being captured into an orbit around the black hole. Such captures release up to 1053 erg of energy, which, at a rate of 1 capture every 105 years is enough to energize the Fermi Bubbles. Two paramount issues require a detailed attention: (i) what is the amount of energy released in a Tidal Disruption Event (TDE) that is available to power the black hole’s surrounding medium, and thus, the Fermi Bubbles and (ii) how is the energy injected into the Fermi Bubbles. This thesis deals with the first point of this quest and looks into the second issue. When a star is scattered from its trajectory and enters in a fatal orbit onto the SMBH, the tidal forces of the black hole overcome the star’s self-gravity disrupting it partially or completely. A fate that depends on the strength of the encounter, which is determined by the proximity of the star to the black hole. Therefore, in order to understand the evolution of the captured star and the energy that is released during the process, a parametric study of the evolution of TDEs, its dependence on the penetration parameter and of their orbit (parabolic and elliptic) was carried out using smoothed particle hydrodynamics simulations. The main results of this work concern the passage of the star at pericentre and the effects on the stellar structure due to the tidal forces of the SMBH. One of such effects caused by these forces is known as the pancake phase as the star acquires a stretched shape during its passage at pericentre. Immediately after this passage the star will develop two tidal tails of debris (gas that is removed from the stellar surface) that can evolve into a narrow stream of gas and the tail faced on to the black hole will fall on a steady rate of accretion onto the compact object. The penetration parameter defines how deep the star falls onto the black hole and the amount of energy that is released by the star. TDEs that result from parabolic orbits represent the cases where larger amounts of energy is released for the surrounding medium in the galactic center and can contribute potentially to power up the Fermi Bubbles; RESUMO: estrelas pelo Buraco Negro Super Massivo Sgr A* no Cento Galáctico Um Buraco Negro Super Massivo (SMBH) com uma massa de ~4 x 106M⊙ reside no centro da Via Láctea e é conhecido como Sagittarius A* (Sgr A*). A sua presença afecta tanto o gás interestelar do centro galáctico, do qual a Zona Molecular Central é um exemplo, assim como o sistema estelar no qual se inclui. Um efeito directo da presença de Sgr A* é a captura de objectos, em particular estrelas, deixando vestígios de emissões de raios X e de raios gama. Um efeito secundário é a origem e energização das Bolhas de Fermi, superbolhas gigantes com cerca de 8 kpc que se estendem acima e abaixo do centro galáctico. O seu conteúdo energético (1055 erg) aponta no sentido da origem se dever a eventos de disrupção de estrelas que são capturadas numa órbita em torno do buraco negro. Estas capturas podem libertar até 1053 erg de energia que, á razão de uma captura a cada 105 anos poderá ser suficiente para energizar as Bolhas de Fermi. Duas questões da maior importância exigem atenção detalhada: (i) qual a quantidade de energia libertada num evento de disrupção de uma estrela que fica disponível para alimentar o meio circundante ao buraco negro, e assim, das Bolhas de Fermi e (ii) como é injectada a energia nas Bolhas de Fermi. Esta tese trabalha na primeira questão e lança a atenção sobre a segunda questão. Quando uma estrela é dispersada da sua trajectória e entra numa órbita fatal em direcção ao SMBH, as forças de maré gravitacional do buraco negro sobrepõem-se á autogravidade da estrela, promovendo a sua disrupção parcial ou total. Este destino depende da força com que o encontro ocorre e é determinado pela proximidade da estrela ao buraco negro. Assim e para compreender a evolução da estrela capturada e a energia que é libertada durante este processo, foi realizado um estudo paramétrico da evolução de eventos de disrupção de estrelas, da sua dependência do parâmetro de penetração e das suas órbitas (parabólicas e elípticas) usando simulações hidrodinâmicas de partículas. Os resultados mais importantes obtidos neste trabalho são relativos á passagem da estrela no pericentro e os efeitos na estrutura estelar devido ás forças por efeito de maré gravitacional do SMBH. Um desses efeitos devido a estas forças é conhecido como a fase da panqueca uma vez que a estrela adquire uma forma achatada durante a sua passagem pelo pericentro. Imediatamente após esta passagem a estrela desenvolve duas estrias de detritos (gás que é removido da superfície da estrela) que evoluem para um longo e estreito sulco de gás e a estria voltada para o buraco negro será atraída numa taxa de acreção estável para o objecto compacto. O parâmetro de penetração define a profundidade com que a estrela é atraída para o buraco negro e a quantidade de energia que esta liberta. Os eventos de disrupção de estrelas em órbitas parabólicas libertam mais energia para o meio circundante no centro galáctico e podem contribuir potencialmente para alimentar as Bolhas de Fermi.

First observed as early as redshift z = 7 and now thought to be found at the centre of every massive galaxy in the local Universe, the evolution history of supermassive black holes (SMBHs) spans over 13 billion years. In this thesis, the coevolution between SMBHs and their host galaxies is studied using a set of hydrodynamical simulations to isolate different components of the interaction between black holes and cosmic gas. The simulations range from black hole accretion in an idealised context to the impact of feedback in the cosmological simulations of the HORIZON suite. The origin of SMBHs during the first billion years of the Universe is a highly non-linear problem, where small-scale behaviour influences large- scale behaviour and vice versa. Gas fuelling a black hole flows from the cosmic web, through its host galaxy and into the black hole's gravitational potential, before eventually reaching its event horizon. Even discounting the complex physical processes at play, resolving the 19 orders of magni- tude in spatial scale involved is beyond the capabilities of current simula- tions. Some of the length scales therefore have to be covered by sub-grid algorithms which need to be able to handle a wide range of environments. Idealised accretion simulations presented in this thesis show that the Bondi-Hoyle-Lyttleton (BHL) accretion algorithm is sufficiently versatile. It automatically determines the accretion rate onto the black hole by the mass flux into its accretion region when the black hole's gravitational po- tential becomes resolved. The accretion rate onto the black hole therefore naturally converges to the correct solution once the size of the accretion region approaches the physical size of the black hole. A drag force algo- rithm that compensates for unresolved dynamical friction, on the other hand, produces a force on the black hole that can unphysically accelerate it relative to the bulk flow of the gas. It needs to be switched off when gas properties are measured within the black hole's gravitational potential. A study of black hole accretion within an isolated cooling halo confirms that the accretion algorithm is able to handle the flow configurations en- countered within an evolving galaxy. To ensure gas is always accreted within the black hole's gravitational potential, a refinement algorithm called "zoom-within-zoom" is introduced in this thesis. It allows the black hole environment to be resolved by orders of magnitude above that of its host galaxy. A low mass seed black hole with a strong drag force early on takes advantage of this extra information during the black hole's early evolution. In the longer term, resolving gas clouds in the black hole vicin- ity to sub-pc scales has a lasting impact on both the mass evolution and duty cycle of massive black holes. Sub-pc size clumps also play a deciding role in the first 200 Myr of evo- lution of a SMBH progenitor in a full cosmological context: 90% of its mass is gained through interactions with dense clumps, which fuel super- Eddington accretion bursts. Once the gas within the host galaxy settles into a rotationally supported disc, star formation and black hole accre- tion slow down. As both primarily occur within the central 30 pc of the compact host galaxy, star formation in proto-galaxies has a major impact on black hole accretion even in the absence of feedback. At low redshift, on the other hand, feedback becomes the crucial link between a SMBH and its host galaxy. A comparison of two simulations from the HORIZON suite, run with and without active galactic nuclei (AGN) feedback respectively, shows that AGN feedback is able to prevent as much as 90% of the stellar mass from forming in the most massive galaxies. Quenching proceeds via a combination of AGN driven outflows and reduced inflows and evolves with redshift as the M_SMBH - M_* relation flattens from z = 5 to z = 0. In conclusion, neither the evolution of galaxies nor that of black holes can be understood without the context of the other. At high redshift, the competition between star formation and black hole accretion inside the compact host galaxy intrinsically links the origin of SMBHs to the early evolution of galaxies. At low redshift, AGN feedback modulates the gas supply of the host galaxy, which has a lasting impact on star formation. The coevolution of black holes and galaxies therefore spans their entire history.

Al centro della maggior parte delle galassie risiedono buchi neri massicci quiescenti. Talvolta questi oggetti possono accrescere materiale dall’ambiente circostante e diventare attivi. Un contributo alla loro accensione è dato dalla distruzione mareale di stelle che gli orbitano intorno. Infatti, le stelle di un cluster nucleare galattico interagiscono stocasticamente una con l’altra, aumentando la probabilità per una di queste di essere scatterata abbastanza vicino al buco nero centrale da risentire in modo significativo della sua influenza mareale. Essenzialmente, se il pericentro della stella attorno al buco nero è minore del cosiddetto raggio mareale, la stella viene completamente distrutta. Una frazione dei detriti stellari prodotti circolarizza e accresce sul buco nero alimentando un’emissione caratteristica. Nonostante la loro rarità e la generale sparsità delle loro osservazioni, sono stati osservati circa 70 candidati, principalmente nelle bande ottica, ultravioletta e X soffice, permettendo così di rivelare buchi neri altrimenti quiescenti. La scoperta di nuovi candidati risulta importante anche per verificare le teorie relative agli eventi di distruzione mareale attraverso le osservazioni. Circa due anni fa ho identificato XMMSL1J063045.9-603110 come nuovo candidato. La sua peculiarità consiste nell’essere associato probabilmente ad una galassia nana molto debole o addirittura ad un globular cluster molto luminoso che ospita un buco nero di massa intermedia. I buchi neri di massa intermedia sono attualmente oggetto di studio come collegamento tra i buchi neri di massa stellare e i buchi neri massicci e come materia prima per la formazione dei buchi neri massicci, pertanto poterli rivelare sarebbe estremamente importante. Principalmente, la letteratura riguardante gli eventi di distruzione mareale tratta le distruzioni mareali totali, ma il profilo dei tidal disruption flares ci si aspetta che dipenda da se la stella viene distrutta totalmente o parzialmente. Per come è definito il raggio mareale, è stato necessario innanzitutto determinare l’effettiva linea di demarcazione tra le distruzioni totali e quelle parziali. Guillochon e Ramirez-Ruiz (2013; 2015) l’hanno valutata attraverso simulazioni idrodinamiche di incontri mareali tra stelle modellate come politropi e buchi neri, basate su un codice a griglia. Seguendo il loro lavoro, ho indagato la stessa questione confrontando codici di simulazione diversi, dotati di differenti vantaggi e limiti. La demarcazione dipendeva in maniera significativa dall’indice politropico scelto (ovvero, dalla struttura interna della stella), ma solo lievemente dal metodo di simulazione utilizzato, al di sopra però di una risoluzione minima. Contrariamente a stelle singole, un gran numero di stelle si trova in sistemi binari. Mandel e Levin (2015) hanno dimostrato che in determinate condizioni entrambe le componenti di una binaria potrebbero essere distrutte marealmente in sequenza subito dopo la rottura mareale della binaria, alimentando così un’emissione totale caratteristica. Da distruzioni mareali doppie ci si aspettano curve di luce a doppio picco. Attraverso simulazioni idrodinamiche di distruzioni mareali doppie, ho dimostrato che possono essere più facilmente osservate curve di luce con una doppia pendenza, piuttosto che a doppio picco, diminuendo l’intensità della distruzione e aumentando la differenza di massa tra le componenti della binaria. Ho identificato la prima evidenza osservativa di questi eventi in PS16dtm. La rivelazione di un flare con doppia pendenza può anticipare l’insorgere di flares periodici se una delle componenti della binaria, solo parzialmente distrutta, rimane legata al buco nero dopo la separazione della binaria.
Quiescent massive black holes live at the centre of most galaxies. Sometimes they can accrete matter from the surroundings and become active. A contribution to the black hole turning on is given by the tidal disruption of stars orbiting around them. Indeed, stars in a galactic nuclear cluster stochastically interact with each other, increasing the probability for one of them to be scattered close enough to the central black hole to significantly feel its tidal influence. Basically, if the pericentre of the star around the black hole is less than about the so-called tidal radius, the star is completely disrupted. A fraction of the produced stellar debris circularises and accretes onto the black hole powering a characteristic flare. Despite their scarcity and general sparseness in observations, about 70 candidates have been observed, mainly in the optical, UV and soft X-ray energy bands, thus allowing the detection of otherwise quiescent black holes. The discovery of new candidates is also important to check the theories about tidal disruption events through observations. About two years ago I classified XMMSL1J063045.9-603110 as a new candidate. Its peculiarity is to be likely associated with a very dim dwarf galaxy or even a very bright globular cluster hosting an intermediate-mass black hole. Intermediate-mass black holes are currently under study as the connecting bridge between stellar-mass and massive black holes and the raw material for massive black holes, thus their detection would be extremely important. Mostly, the literature of tidal disruption events deals with total tidal disruptions, but the appearance of tidal disruption flares is expected to depend on whether the star is fully or partially disrupted. Given the tidal radius definition, it first followed the need to define the effective demarcation line between total and partial disruptions. Guillochon & Ramirez-Ruiz (2013; 2015) evaluated it through grid-based hydrodynamical simulations of tidal encounters between polytropic stars and black holes. Following their work, I investigated the same problem by comparing different simulation codes, which have different advantages and limits. The demarcation distance depended significantly on the chosen polytropic index (i.e. on the stellar internal structure), but only weakly on the adopted simulation method, provided a minimum resolution threshold. As opposed to single stars, a great number of field stars are in binaries. Mandel & Levin (2015) demonstrated that under certain conditions both stars in a binary might be tidally disrupted in sequence immediately after the tidal binary break-up, thus powering a peculiar total accretion flare. Double-peaked light curves are expected to rise from double tidal disruptions. Via hydrodynamical simulations of double tidal disruptions, I demonstrated that kneed light curves, rather than double-peaked ones, can be more easily observed when decreasing the strength of the disruption and when elevating the mass difference between the binary components. I identified the first observational evidence of such events in PS16dtm. The detection of a knee can anticipate the onset of periodic flares if one of the binary components, only partially disrupted, remains bound to the black hole after binary separation.

The application of Computer Graphics tools in the nature phenomena simulation have been presenting a series of proposals since its creation. Over the years this task has gained a characteristic trait that makes it closer to the reality, both visually as by the abstraction strategies used. However, the specific application of this Computer Science area for the astrophysical phenomena simulation remains as something restricted explored, although the Computer Graphics is considered as an important tool to aid the synthesis of satellite images and the film industry. Accordingly, this graphical simulation area remains open in several ways, showing a need for development of simulation models for the phenomena described by Astrophysics. This dissertation presents a graphical simulation model of Black Holes, that is one of the most mysterious phenomena known by man, through the use of Particle Systems representation techniques and the approximation method Smoothed Particle Hydrodynamics, making possible this phenomenon observation and its application in the animations design.
A aplicação da Computação Gráfica na simulação de fenômenos da natureza tem apresentado, desde sua criação, uma série de propostas, que ao longo dos anos vem ganhando um caráter que as aproxima mais da realidade, tanto visualmente quanto através das estratégias de abstração utilizadas. Entretanto, a aplicação específica desta área da Ciência da Computação para a simulação de fenômenos astrofísicos fisicamente baseados ainda permanece como algo restritamente explorado, embora a Computação Gráfica seja considerada como uma importante ferramenta de auxílio a síntese de imagens obtidas via satélite e na industria cinematográfica. Neste sentido, esta área de simulação gráfica permanece em aberto sob diversos aspectos, denotando uma necessidade de concepção de modelos de simulação para os fenômenos descritos pela Astrofísica. Nesta dissertação será apresentado um modelo de simulação gráfica de Buracos Negros, um dos fenômenos mais misteriosos conhecidos pelo homem, através da utilização da técnica de representação Sistemas de Partículas e do método de aproximação Smoothed Particle Hydrodynamics, tornando possível a observação deste fenômeno e sua aplicação na concepção de animações.
Mestre em Ciência da Computação

One of the exciting discoveries from the recent X-ray spectroscopic studies of active galactic nuclei (AGNs) is the so called "relativistically-broadened iron fluorescent emission line" often detected in the hard X-ray spectra. It is generally believed to originate from the inner part of the accretion disk surrounding a supermassive black hole (BH) at the center. Although we have begun to obtain some physical insight regarding such emission lines supported by theoretical models (e.g., disk-corona model), exactly how and where the observed fluorescence may take place is still disputable. Here, an X-ray data with XMM-Newton Observatory of a typical narrow-line Seyfert 1 galaxy, NGC 4051, is analyzed based on a partial covering model to consistently explain the observed time-resolved temporal/spectral variations. This model implies that the intrinsic emission varies significantly in the presence of the covering cloud. We often detect a hard X-ray continuum originating from a hot region close to the central engines of AGNs. As a promising X-ray source candidate, relativistic hydrodynamic (HD) shocks are investigated systematically and then extended to the magnetohydrodynamic (MHD) shocks, given the widely accepted suggestion that the presence of the magnetic fields could play an important role in the accreting flows. I show that both HD and MHD shocks can form in the vicinity of the BH, perhaps responsible for creating such a high temperature region where hard X-rays are produced. Particularly in the MHD shocked plasma, the hydro/magneto-dominated states are found. Considering the effect of such magnetic fields in the accretion disk, I calculate nonstandard iron fluorescent line profiles in the presence of spiral density waves and find multiple sharp sub-peak structures in extremely skewed line profiles, which will be detectable with upcoming X-ray satellites such as Astro-E2 XRS for testing the model. This dissertation is the result of my own work and also includes some work done in collaboration. Parts of this dissertation have been either already published in or submitted to the Astrophysical Journal and presented at conferences, while some are still in progress.

Les jets sont des phénomènes d’éjection collimatée de plasma magnétisé. Ces ph́énomènes liés à l’accrétion d’un disque sur un objet central, sont relativement répandus dans l’univers : les environnement des étoiles jeunes (objets Herbig-Haro, étoiles T Tauri), des binaires X, des sursauts gamma et les noyaux actifs de galaxies... Les jets extra-galactiques sont issus des trous noirs super-massifs au centre de galaxies telles que les quasars ou les radiogalaxies. Ils sont caractérisés par leur taille, leur puissance et la vitesse du plasma.Les jets extragalactiques sont étudiés dans de ce travail de thèse, même si les outils et méthodes développés peuvent être utilisés pour les binaires X et les micro-quasars. Nous poserons en particulier les questions des mécanismes de lancement, d’accélération et de collimation de ces écoulements. Nous traiterons également de la source énergétique à l’origine de l’écoulement qui peut atteindre une puissance de l’ordre de 10^47 erg.s−1.Le liens avec l’accrétion, la proximité de la base des jets avec le trou noir central, les vitesses d’écoulement observées dans certains jets, montrent que le traitement de ces questions doit inclure les effets de la relativité générale. Nous étudierons donc des solutions de la décomposition 3+1 des équations de la magnéto-hydrodynamique en métrique de Kerr. Nous nous appliquerons au développement d’un modèle d’écoulement méridional auto-similaire avec un traitement consistant du cylindre de lumière. Ce modèle pouvant s’appliquer à la fois au jet et à l’accrétion. Nous explorons les mécanismes d’accélération et de collimation des solutions produites. Nous calculerons des solutions de l’écoulement entrant dans l’horizon et de l’écoulement sortant à l’infini incluant des termes d’injection de paires. Le rôle du mécanisme de création de paires et des processus d’extraction de l’énergie du trou noir sera exploré
Jets are collimated ejection phenomena of magnetized plasma. These phenomena related to the accretion of a disk on a central object, are relatively common in the universe: the environment of young stars (Herbig- Haro Objects, T Tauri stars...), X-ray binaries, Gamma-ray-bursts, and active galactic nuclei... Extragalactic jets come from super-massive black holes in the center of galaxies such as quasars or radiogalaxies. They are characterized by their size, their power and velecity of the plasma.Extragalactic jets will be the subject of studies in this thesis work, although the tools and methods developed can be used for X-ray binaries and microquasars. In particular, we will ask questions about the mechanisms of launching, accelerating and collimating these flows, but also about the energy source at the origin of the flow that can reach a power in the order of 10^47erg.s−1.The links with the accretion, the proximity of the jet base to the central black hole, flow velocities observed in some jets, show that the treatment of these issues must include the effects of general relativity. We will therefore study solutions of the 3+1 decomposition of magneto-hydrodynamic equations in Kerr metric. We will apply ourselves the development of a meridional self-similar magnetized flow model with a consistent treatment of the light cylinder effect. This model can be applied to both spine jet and accretion. We explore the mechanisms of acceleration and collimation of the obtained solutions. We will calculate solutions of the incoming flow in the horizon and the outgoing flow reaching infinity including injection terms. The role of the pair creation mechanism and the processes of extracting energy from the black hole are explored

The work of this dissertation will study various aspects of the dynamics of compact objects using numerical simulations.We consider BH dynamics within two modified or alternative theories of gravity. Within a family of Einstein-Maxwell-Dilaton-Axion theories, we find that the GW waveforms from binary black hole (BBH) mergers differ from the standard GW waveform prediction of GR for especially large axion values. For more astrophysically realistic (i.e. smaller) values, the differences become negligible and undetectable. Weestablish the existence of a well-posed initial value problem for a second alternative theory fo gravity (quadratic gravity) and demonstrate in spherical symmetry that a linear instability is effectively removed on consideration of the full nonlinear theory.We describe the key components and development of a code for studying BBH mergers for which the mass ratio of the binaries is not close to one. Such intermediate mass ratio inspirals (IMRIs) are much more difficult to simulate and present greater demands on resolution, distributed computing, accuracy and efficiency. To this end, we present a highly-scalable framework that combines a parallel octree-refined adaptive mesh with a wavelet adaptive multiresolution approach. We give results for IMRIs with mass ratios up to 100:1. We study the ejecta from BNS in Newtonian gravity. Using smoothed particle hydrodynamics we develop and present the highly scalable FleCSPH code to simulate such mergers. As part of the ejecta analysis, we consider these mergers and their aftermath as prime candidates for heavy element creation and calculate r-process nucleosynthesis within the post-merger ejecta. Lastly we consider a non-standard, yet increasingly explored, interaction between a BH and a NS that serves as a toy model for primordial black holes (PBH) and their possible role as dark matter candidates. We present results from a study of such systems in which a small BH forms at the center of a NS. Evolving the spherically symmetric system in full GR, we follow the complete dynamics as the small BH consumes the NS from within. Using numerical simulations, we examine the time scale for the NS to collapse into the PBH and show that essentially nothing remains behind. As a result, and in contradiction to other claims in the literature, we conclude that thisis an unlikely site for ejecta and nucleosynthesis, at least in spherical symmetry.

Ventos (em inglês outflows) de ampla abertura e larga escala sâo uma característica comum em galáxias ativas, como as galáxias Seyfert. Em sistemas como este, onde buracos negros supermassivos (em inglês super massive black holes, SMBHs) de núcleos galácticos ativos de galáxias (em inglês active galactic nuclei, AGN) coexistem com regiões de formação estelar (em inglês star forming, SF), nâo está claro das observações se o AGN SMBH ou o SF (ou ambos) são responsaveis pela indução desses ventos. Neste trabalho, estudamos como ambos podem influenciar a evolução da galáxia hospedeira e seus outflows, considerando galáxias tipo Seyfert nas escalas de kilo-parsec (kpc). Para este objetivo, estendemos o trabalho anterior desenvolvido por Melioli & de Gouveia Dal Pino (2015), que considerou ventos puramente hidrodinâmicos impulsionados tanto pela SF quanto pelo AGN, mas levando em conta para este último apenas ventos bem estreitos (colimados). A fim de obter uma melhor compreensão da influencia (feedback) desses mecanismos sobre a evolução da galáxia e seus outflows, incluímos também os efeitos de ventos de AGN com maior ângulo de abertura, já que ventos em forma de cone podem melhorar a interação com o meio interestelar da galáxia e assim, empurrar mais gás nos outflows. Além disso, incluímos também os efeitos dos campos magnéticos no vento, já que estes podem, potencialmente, ajudar a preservar as estruturas e acelerar os outflows. Realizamos simulações tridimensionais magneto-hidrodinâmicas (MHD) considerando o resfriamento radiativo em equilíbrio de ionização e os efeitos dos ventos do AGN com dois diferentes ângulos de abertura (0º e 10º) e razões entre a pressão térmica e a pressão magnética beta=infinito, = 300 e 30, correspondentes a campos magnéticos 0, 0,76 micro-Gauss e 2,4 micro-Gauss respectivamente. Os resultados de nossas simulações mostram que os ventos impulsionados pelos produtos de SF (isto é, pelas explosões de supernovas, SNe) podem direcionar ventos com velocidades 100-1000 km s¹, taxas de perda de massa da ordem de 50 Massas solares/ano, densidades de ~1-10 cm-3 e temperaturas entre 10 e 10 K, que se assemelham às propriedades dos denominados absorvedores de calor (em inglês warm absorbers, WAs) e também são compatíveis com as velocidades dos outflows moleculares observadas. No entanto, as densidades obtidas nas simulações são muito pequenas e as temperaturas são muito grandes para explicar os valores observados nos outflows moleculares (que têm n ~150-300 cm³ e T<1000 K). Ventos colimados de AGN (sem a presença de ventos SF) também são incapazes de conduzir outflows, mas podem acelerar estruturas a velocidades muito altas, da ordem de ~10.000 km s¹ e temperaturas T> 10 K, tal como observado em ventos ultra rapidos (em inglês, ultra-fast outflows, UFOs). A introdução do vento de AGN, particularmente com um grande ângulo de abertura, causa a formação de estruturas semelhantes a fontes galácticas. Isso faz com que parte do gás em expansão (que está sendo empurrado pelo vento de SF) retorne para a galáxia, produzindo um feedback \'positivo\' na evolução da galáxia hospedeira. Descobrimos que esses efeitos são mais pronunciados na presença de campos magnéticos, devido à ação de forças magnéticas extras pelo vento AGN, o qual intensifica o efeito de retorno do gás (fallback), e ao mesmo tempo reduz a taxa de perda de massa nos outflows por fatores de até 10. Além disso, a presença de um vento de AGN colimado (0º) causa uma remoção significativa da massa do núcleo da galáxia em poucos 100.000 anos, mas este é logo reabastecido pelo de gás acretante proveniente do meio interestelar (ISM) à medida que as explosões de SNe se sucedem. Por outro lado, um vento de AGN com um grande ângulo de abertura, em presença de campos magnéticos, remove o gás nuclear inteiramente em alguns 100.000 anos e não permite o reabastecimento posterior pelo ISM. Portanto, extingue a acreção de combustível e de massa no SMBH. Isso indica que o ciclo de trabalho desses outflows é de cerca de alguns 100.000 anos, compatível com as escalas de tempo inferidas para os UFOs e outflows moleculares observados. Em resumo, os modelos que incluem ventos de AGN com um ângulo de abertura maior e campos magnéticos, levam a velocidades médias muito maiores que os modelos sem vento de AGN, e também permitem que mais gás seja acelerado para velocidades máximas em torno de ~10 km s¹, com densidades e temperaturas compatíveis com aquelas observadas em UFOs. No entanto, as estruturas com velocidades intermediárias de vários ~100 km s¹ e densidades até uns poucos 100 cm³, que de fato poderiam reproduzir os outflows moleculares observados, têm temperaturas que são muito grandes para explicar as características observadas nos outflows moleculares, que tem temperaturas T< 1000 K. Além disso, estes ventos de AGN não colimados em presença de campos magnéticos entre T< 1000 K. Alem disso, estes grandes ventos AGN de angulo de abertura em fluxos magnetizados reduzem as taxas de perda de massa dos outflows para valores menores que aqueles observados tanto em outflows moleculares quanto em UFOs. Em trabalhos futuros, pretendemos estender o espaço paramétrico aqui investigado e também incluir novos ingredientes em nossos modelos, como o resfriamento radioativo fora do equilíbrio, a fim de tentar reproduzir as características acima que não foram explicadas pelo modelo atual.
Large-scale broad outflows are a common feature in active galaxies, like Seyfert galaxies. In systems like this, where supermassive black hole (SMBH) active galactic nuclei (AGN) coexist with star-forming (SF) regions it is unclear from the observations if the SMBH AGN or the SF (or both) are driving these outflows. In this work, we have studied how both may influence the evolution of the host galaxy and its outflows, considering Seyfert-like galaxies at kilo-parsec (kpc) scales. For this aim, we have extended previous work developed by Melioli & de Gouveia Dal Pino (2015), who considered purely hydrodynamical outflows driven by both SF and AGN, but considering for the latter only very narrow (collimated) winds. In order to achieve a better understanding of the feedback of these mechanisms on the galaxy evolution and its outflows, here we have included the effects of AGN winds with a larger opening angle too, since conic-shaped winds can improve the interaction with the interstellar medium of the galaxy and thus push more gas into the outflows. Besides, we have also included the effects of magnetic fields in the flow, since these can potentially help to preserve the structures and speed up the outflows. We have performed three-dimensional magneto-hydrodynamical (MHD) simulations considering equilibrium radiative cooling and the effects of AGN-winds with two different opening angles (0º and 10º), and thermal pressure to magnetic pressure ratios of beta=infinite, 300 and 30 corresponding to magnetic fields 0, 0.76 micro-Gauss and 2.4 micro-Gauss, respectively. The results of our simulations show that the winds driven by the products of SF (i.e., by explosions of supernovae, SNe) alone can drive outflows with velocities ~100-1000 km s¹, mass outflow rates of the order of 50 Solar Masses yr¹, densities of ~1-10 cm³, and temperatures between 10 and 10 K, which resemble the properties of warm absorbers (WAs) and are also compatible with the velocities of the observed molecular outflows. However, the obtained densities from the simulations are too small and the temperatures too large to explain the observed values in molecular outflows (which have n ~ 150-300 cm³ and T<1000 K). Collimated AGN winds alone (without the presence of SF-winds) are also unable to drive hese outflows, but they can accelerate structures to very high speeds, of the order of ~ 10.000 km s¹, and temperatures T> 10 K as observed in ultra-fast outflows (UFOs). The introduction of an AGN wind, particularly with a large opening angle, causes the formation of fountain-like structures. This makes part of the expanding gas (pushed by the SF-wind) to fallback into the galaxy producing a \'positive\' feedback on the host galaxy evolution. We have found that these effects are more pronounced in presence of magnetic fields, due to the action of extra magnetic forces by the AGN wind producing enhanced fallback that reduces the mass loss rate in the outflows by factors up to 10. Furthermore, the presence of a collimated AGN wind (0º) causes a significant removal of mass from the core region in a few 100.000 yr, but this is soon replenished by gas inflow from the interstellar medium (ISM) when the SNe explosions fully develop. On the other hand, an AGN wind with a large opening angle in presence of magnetic fields is able to remove the nuclear gas entirely within a few 100.000 yr and does not allow for later replenishment. Therefore, it quenches the fueling and mass accretion onto the SMBH. This indicates that the duty cycle of these outflows is around a few 100.000 yr, compatible with the time-scales inferred for the observed UFOs and molecular outflows. In summary, models that include AGN winds with a larger opening angle and magnetic fields, lead to to be accelerated to maximum velocities around 10 km s¹ (than models with collimated AGN winds), with densities and temperatures which are compatible with those observed in UFOs. However, the structures with intermediate velocities of several ~100 km s¹ and densities up to a few 100 cm3, that in fact could reproduce the observed molecular outflows, have temperatures which are too large to explain the observed molecular features, which have temperatures T<1000 K. Besides, these large opening angle AGN winds in magnetized flows reduce the mass loss rates of the outflows to values smaller than those observed both in molecular outflows and UFOs. In future work, we intend to extend the parametric space here investigated and also include new ingredients in our models, such as non-equilibrium radiative cooling, in order to try to reproduce the features above that were not explained by the current model.

Coral reefs are largely restricted to shallow tropical seas, where water is warm, nutrient poor and well illuminated for photosynthesis and where sufficient calcium carbonate (aragonite) exists in seawater for the precipitation of coral skeletons (i.e. calcification). Extreme temperatures and salinities cause thermal and osmotic stress, while large amounts of sediment smother corals and block light. High concentrations of nutrients encourage algal growth at the expense of corals, while low seawater aragonite concentrations prevent net accretion of the reef framework. At local scales, the hydrodynamic regime influences reef growth, as corals are damaged by storms and wave surge. The typical abiotic environment in which reefs are found, and which determines reef distribution, is defined. The chapter also discusses marginal reefs, where corals live at the margins of their survival, for example in the warm, salty seas of the Persian Gulf and the relatively cold waters of Australia’s Lord Howe Island.