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Dissertations / Theses on the topic 'Accretion; gravitational'

Author: Grafiati

Published: 3 June 2025

Last updated: 31 July 2025

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1

Schneck, Kristiana E. (Kristiana Elizabeth). "Gravitational influences on magnetic field structure in accretion disks." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61266.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 53).<br>Black holes and compact objects are often surrounded by structures known as accretion disks which consist of ionized plasma. Due to the immense forces present in the disk, interesting and complex magnetic field structures can be set up within the disk. The influence of gravity on these structures is explored via a higher-order expansion of the gravitational potential. We consider several cases: the case when the Lorentz force

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2

Lin, Min-Kai, and Kaitlin M. Kratter. "ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621384.

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Low mass, self-gravitating accretion disks admit quasi-steady, "gravito-turbulent" states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces

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3

Britsch, Markward. "Gravitational instability and fragmentation of self-gravitating accretion disks." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-69667.

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4

Poindexter, Shawn David. "Sharpening The Tools of Gravitational Microlensing." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1258766992.

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5

Morgan, Christopher Warren. "Quasar Structure from Microlensing in Gravitationally Lensed Quasars." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1205848751.

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6

Britsch, Markward [Verfasser], and Wolfgang [Akademischer Betreuer] Duschl. "Gravitational instability and fragmentation of self-gravitating accretion disks / Markward Britsch ; Betreuer: Wolfgang Duschl." Heidelberg : Universitätsbibliothek Heidelberg, 2006. http://d-nb.info/1178678075/34.

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7

Brown, Jacqueline. "Surging Seepage: A Triple Bond Accretion System." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1481.

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My current work revels in a state of flux. I strive for the work to be electrically charged, conveying a feverish sense of immediacy and vitality that implies motion and frenetic energy. The work is an accretion of brightly colored biomorphic forms that extend out from the wall and onto the floor. Viscous parts ooze and drip while others are globular and bulbous. The hyper-organic forms suggest a paradoxical state of both ripening and rotting, becoming and unbecoming. The work is an attempt to traverse between seemingly divergent constructs, some of which include: growth and decay, the artifi

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8

Feltre, Anna. "Multi-band Emission of Active Galactic Nuclei: the Relationship of Stellar and Gravitational-Accretion Activity." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423457.

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One of the remaining open issues in the context of the analysis of active galactic nuclei is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst activity. What is, in this picture, the role played by the obscuring dust around the nucleus and what does the state of the art models have to say? Can the infrared data provided by Spitzer and Herschel help us in extensively investigate both phenomena and, if so, how and with what limitations? Does the presence of an active nucleus have an impact in the mid- and far-infrared properties of galaxies? Which a

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9

TOSCANI, MARTINA. "TIDAL DISRUPTION EVENTS IN THE ERA OF MULTIMESSENGER ASTRONOMY." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/874970.

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Tidal Disruption Events (TDEs) occur when a star, wandering too close to a black hole (BH), is torn apart by BH tides. After the disruption, roughly half of the stellar debris is expected to circularize around the BH and eventually form an accretion disc. These events represent a unique way to detect BHs through the universe since they emit both electromagnetic (EM) radiation and gravitational waves (GWs). In fact, after returning to the pericenter, the stellar material accretes onto the central object, producing very luminous EM flares. To date, around 50 robust TDEs have been detected in di

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10

Stone, Nicholas Chamberlain. "Tidal Disruption of Stars by Supermassive Black Holes." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10998.

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This thesis presents theoretical results on the tidal disruption of stars by supermassive black holes (SMBHs). The multiwavelength ares produced by tidal disruption events (TDEs) have supernova-like luminosities, and associated relativistic jets can be visible to cosmological distances. TDEs probe the demography of quiescent SMBHs, and are natural laboratories for jet launching mechanisms and super-Eddington accretion. The first chapter broadly surveys TDE physics. The second and third chapters estimate the TDE rate following gravitational wave (GW) recoil of a SMBH (after a SMBH binary merger

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11

Siregar, Edouard. "Etude de la stabilite des disques d'accretion en astrophysique." Toulouse 3, 1987. http://www.theses.fr/1987TOU30268.

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Etude hydrodynamique du phenomene d'accretion sur un objet compact et stabilite dynamique d'un tel ecoulement. On effectue une simulation numerique d'un flot bidimensionnel keplerien pour permettre d'estimer l'echelle de temps dynamique en fonction de la turbulence

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12

Moriyama, Kotaro. "New methods for probing black-hole space-time based on infalling gas clouds." Kyoto University, 2018. http://hdl.handle.net/2433/232254.

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13

Johannsen, Tim. "Testing General Relativity in the Strong-Field Regime with Observations of Black Holes in the Electromagnetic Spectrum." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/238893.

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General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-K

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14

Mamatsashvili, George. "Dynamics of perturbation modes in protoplanetary discs : new effects of self-gravity and velocity shear." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5283.

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Protoplanetary discs, composed of gas and dust, usually surround young stellar objects and serve two main purposes: they determine the accretion of matter onto the central object and also represent sites of planet formation. The accretion proceeds through the transport of angular momentum outwards allowing the disc matter to fall towards the centre. A mechanism responsible for the transport can be turbulence, waves or other coherent structures originating from various instabilities in discs that could, in addition, play a role in the planet formation process. For an understanding of these inst

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15

CUOFANO, Carmine. "Magnetic fields generated by r-modes in accreting millisecond pulsars." Doctoral thesis, Università degli studi di Ferrara, 2010. http://hdl.handle.net/11392/2389313.

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In rotating neutron stars the existence of the Coriolis force allows the presence of the so-called Rossby oscillations (r-modes) which are known to be unstable to emission of gravitational waves. In the Thesis, for the first time, we introduce the magnetic damping rate in the evolution equations of r-modes. We show that r-modes can generate very strong toroidal fields in the core of accreting millisecond pulsars by inducing differential rotation. We shortly discuss the instabilities of the generated magnetic field and its long time-scale evolution in order to clarify how the generated mag

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16

Trova, Audrey. "Gravité des systèmes verticalement homogènes : applications aux disques astrophysiques." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00955555.

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La gravitation joue un rôle important dans de nombreux domaines de l'astrophysique : elle assure notamment la cohésion et la stabilité des planètes, des étoiles et des disques. Elle est aussi motrice dans le processus d'effondrement de structure et conduit, dès lors qu'un moment cinétique initial est significatif, à la formation d'un disque.Ma thèse est consacrée à l'étude des disques de gaz, et plus particulièrement à la description du potentiel et du champ de gravité qu'ils génèrent dans l'espace et sur eux-mêmes (l'auto-gravitation). Bien que la force de Newton soit connue depuis longtemps,

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17

BECERRA, BAYONA LAURA MARCELA. "Accretion on compact stars: hypercritical accretion in the Induced Gravitational Collapse and the post-merger evolution of white dwarfs mergers." Doctoral thesis, 2018. http://hdl.handle.net/11573/1103937.

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The Induced Gravitational Collapse (IGC) paradigm points to a binary origin for the long-duration gamma-ray burst (GRBs) associated with supernovae (SN). In this one, a carbon-oxygen core (COcore) explodes in a Type Ib/c SN in presence of a close neutron star (NS) companion. The SN triggers an hypercritical accretion into the NS and depending on the initial binary parameters, two outcomes are possible. In a first scenario, also referred as binary-driven hypernova (BdHNe), the binary is enough tight, so the accretion rate onto NS can be enough high to lead the NS reaches its critical mass, a

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18

Herbst, Rhameez Sheldon. "Numerical simulations of isothermal collapse and the relation to steady-state accretion." Thesis, 2015. http://hdl.handle.net/10539/18563.

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A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of Science School of Computational and Applied Mathematics. May 2015.<br>In this thesis we present numerical simulations of the gravitational collapse of isothermal clouds of one solar mass at a temperature of 10K. We will consider two types of initial conditions – initially uniform spheres and perturbed Bonnor-Ebert spheres. The aim of the performed numerical simulations is to investigate the core bounce described by Hayashi and Nakano [1]. They reported that if strong enough, the

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19

Bate, Nicholas Frazer. "Quasar microimaging." 2010. http://repository.unimelb.edu.au/10187/7068.

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Observations of gravitationally microlensed quasars offer a unique opportunity to probe quasar structure on extremely small scales. In this thesis, we conduct extensive microlensing simulations and compare with observational data to constrain quasar accretion discs, and conduct preliminary probes of broad emission line region structure. This analysis is done using a new single-epoch imaging technique that requires very little telescope time, and yet produces results that are comparable to those obtained from long-term monitoring campaigns.<br>We begin by exploring the impact of variable smooth

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20

Ledvina, Lukáš. "Mapování akrečního disku kvasaru gravitačním mikročočkováním." Master's thesis, 2014. http://www.nusl.cz/ntk/nusl-336604.

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Quasar microlensing is a relatively newly explored phenomenon, which is ideally suited for studying the spatial distribution of emission from the innermost accretion disc. By now we know many macrolensed quasars, in which we can observe multiple images formed by the deflection of light in the gravitational field of an intervening galaxy. In case one of these images passes directly through the stellar population of the galaxy, it can be additionally microlensed by individual stars. The gravitational field of these stars forms a caustic network for light passing by. When a quasar accretion disc

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21

John, Anslyn James. "Stellar structure and accretion in gravitating systems." Thesis, 2012. http://hdl.handle.net/10413/10640.

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In this thesis we study classes of static spherically symmetric solutions to the Einstein and Einstein–Maxwell equations that may be used to model the interior of compact stars. We also study the spherical accretion of fluids on to bodies in both general relativity and the Newtonian theory of gravity. The condition for pressure isotropy is obtained upon specifying one of the gravitational potentials and the electric field intensity. A series solution was found after specifying a cubic form for the potential. The pressure and energy density appear to be non–singular and continuous inside the st

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22

Wette, Karl. "Gravitational waves from accreting neutron stars and Cassiopeia A." Phd thesis, 2009. http://hdl.handle.net/1885/7354.

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This thesis is concerned with the mysteries of neutron stars and the quest for gravitational waves. Rapidly-rotating neutron stars are anticipated sources of periodic gravitational waves, and are expected to be detectable within the next decade using kilometre-scale laser interferometry. We first perform ideal-magnetohydrodynamic axisymmetric simulations of a magnetically confined mountain on an accreting neutron star. Two scenarios are considered, in which the mountain sits atop a hard surface or sinks into a soft, fluid base. We quantify the ellipticity of the star, due to a mountain grown o

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23

Witzany, Vojtěch. "Chaos v polích deformovaných černých děr." Master's thesis, 2015. http://www.nusl.cz/ntk/nusl-350874.

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The consequences of two key approximations of accretion-disc physics near black holes are studied in this thesis. First, the question of effective ``pseudo-Newtonian" potentials mimicking a black hole is investigated both through numerical simulations and analytical means, and second, the neglect of additional gravitating matter near accreted-upon black holes and its consequences are put to test. After some broader discussion of integrability, resonance and chaos, a general "pseudo-Newtonian" limit for geodesic motion is derived, and applied for the case of null geodesics near a glowing toroid

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24

Mondal, Tushar. "Magnetically arrested advective accretion flows around black holes and their implications to ultraluminous X-ray sources and blazars." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/5208.

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Black hole (BH) accretions are very powerful sources of energy in the universe. In accretion phenomena, the surrounding gas spirals down towards the central BH and forms a disc or quasi-spherical structure based on the outward transport of angular momentum. At the same time, the enormous gravitational potential energy of a BH is released as heat and radiation. However, the presence of strong magnetic fields can alter the underlying radiation mechanisms and thermodynamic properties. Theoretical and observational inferences indicate a signature of dynamically dominant magnetic fields in the vici

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