Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 48 for “"accretion disks"”.
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Magnetically torqued thin accretion disks
We consider geometrically thin accretion disks around millisecond X-ray pulsars. We start with the Shakura-Sunyaev thin disk model as a basis and modify the disk equations with a magnetic torque from the central neutron star. Disk solutions are computed for a range of neutron star magnetic fields. …
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Accretion disks in the cataclysmic variables
… structure of gaseous circumstellar disks in vertical hydrostatic equilibrium are derived. The possibility of turbulent instablilty and the resulting viscosity laws are discussed.
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Resistive magnetohydrodynamic jets from protostellar accretion disks
Astrophysikalische Jets sind ausgedehnte, kollimierte Massenausflüsse von verschiedenen astronomischen Objekten. Zeitabhängige magnetohydrodynamische (MHD) Simulationen der Jet-Entwicklung müssen den Akrretionsprozess in der Scheibe berücksichtigen, da der Jet aus der Scheibenmaterie gespeist wird. …
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Hydrodynamic and Magnetohydrodynamic Convection in Accretion Disks
… of convection perpendicular to the plane of accretion disks have been discussed for several decades. Recent simulations combining convection and the magnetorotational instability have given fresh impetus to the debate, as the interplay of the two processes can enhance angular momentum …
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Shear instabilities between accretion disks and nova objects
… on the surface of white dwarfs caused by accretion from a companion star. Most studies focus on modelling the explosive phase (thermonuclear runaway), while this thesis, instead, focuses on the pre-explosion stage, investigating how shear instabilities and accretion-driven dynamics affect …
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Multiwavelength studies of accretion disks around compact objects
… for spectral flattening, and cannot rule out an accretion disk scenario for AXPs.
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Magneto-centrifugal Wind with Applications to Astrophysical Accretion Disks
… potential solution at low mass loading. Gaseous disks in star-forming galaxies and active galactic nuclei may contain dynamically important magnetic fields and significant flux of cosmic rays. In contrast with radiation-pressure dominated disks, a much weaker energy input in cosmic rays is …
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Gravitational instability and fragmentation of self-gravitating accretion disks
… of two large gas-rich galaxies followed by disk accretion. This model relies on a large enough turbulent viscosity in the disk. We show in a linear stability analysis of thin self-gravitating viscous disks that the gravitational instability can drive a turbulence generating the $\beta$-viscosity. …
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Turbulent Angular Momentum Transport in Weakly-Ionized Accretion Disks
Accretion disks are ubiquitous in the universe. Although difficult to observe directly, their presence is often inferred from the unique signature they imprint on the spectra of the systems in which they are observed. In addition, many properties of accretion-disk systems that would be otherwise …
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Gravitational influences on magnetic field structure in accretion disks
… 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 …
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Zooming in on quasar accretion disks using chromatic microlensing
Observing the temperature profiles of accretion disks around black holes is a fundamental test of an important astrophysical process. However, angular resolution limitations have prevented such a measurement for distant quasars. We present a new method for determining the size of quasar accretion …
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Magnetic jets from accretion disks : field structure and X-ray emission
Astrophysikalische Jets sind stark kollimierte Materieströmungen hoher Geschwindigkeit. Sie stehen im Zusammenhang mit einer Fülle verschiedener astrophysikalischer Objekte wie jungen Sternen, stellaren schwarzen Löchern ('Mikro-Quasare'), Galaxien mit aktivem Kern (AGN) und wahrscheinlich auch mit …
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General relativistic radiation magnetohydrodynamics, with applications to black hole accretion disks
Electron temperatures in the inner region of accretion disks around black holes are set by the balance of advection, viscous heating, and radiative interactions. At the lowest accretion rates, radiative processes may be safely ignored, and electrons are nearly virial. Advection carries the lion's …
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Magnetic Field Evolution in Black Hole Accretion Disks and Relativistic Jets
… about their role around SMBHs generally, and in accretion and the launching of relativistic jets in particular. This thesis aims to tackle both topics using three-dimensional magnetohydrodynamics (MHD) and relativistic magnetohydrodynamics (RMHD) simulations. In the first half (Chapters 2 and 3), …
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General-relativistic magnetohydrodynamics simulations of black hole accretion disks: dynamics and radiative properties
… in this thesis is to understand the black hole accretion process and predict its observational properties. The highly non-linear process involves a turbulent magnetized plasma in a general relativistic regime, thus making it hard to study analytically. We use numerical simulations, specifically …
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Neutron Star Mergers at the Dawn of Multimessenger Astrophysics: massive binaries, accretion disks and phase transitions
… of April, 2019, on the characterization of the accretion discs formed from the merger of a binary system composed by two neutron stars and on the effects of a hadron to quark phase transition that can occurs during such mergers.
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Perturbation approach for the radiative transfer equation for 3D moving media and application to accretion disks
Die mehrdimensionale Strahlungstransportgleichung wird mit Hilfe einer stoerungstheoretischen Methode geloest, wobei sich die vollstaendige Loesung durch eine Reihe von 1D Loesungen ergibt. Da die Loesungen von Stoerungen hoeherer Ordnung explizit angegeben werden koennen und die Verfahren, die …
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Local Numerical Models of Turbulent Accretion Flows
… for driving angular momentum transport in accretion disks. This work provides a comprehensive study of MHD turbulent accretion flow using shearing box simulations.
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A Numerical Study of Nonspherical Black Hole Accretion
… The aim is to study fully dynamic inviscid fluid accretion onto black holes, as well as to study the evolution and development of nonlinear instabilities in pressure supported accretion disks.
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Magnetohydrodynamical phenomena in gaseous disks
… and influence of magnetic fields in gaseous disks. It builds mainly on the work of Vainstein and Ruzmaiken (1972) on the generation of galactic magnetic fields. Emphasis here is on application to accretion disks in the cataclysmic variables (CVs). These include novae, dwarf novae and …
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