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 50 for “"Accretion Disk"”.
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Radial-zoned thermal accretion disk model around black holes
… in high energy astrophysics, the theory of accretion disks around black holes. Accretion disk models are applied to the dynamics of compact objects surrounded by material with organized angular momentum. The disk forms due to the process by which differentially rotating fluid layers interact …
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Spectral Comparisons of Neutron Star Low-Mass X-Ray Binaries with Black Hole X-Ray Binaries
… the investigation of the innermost parts of the accretion disk and immediate surroundings of the compact object. The weak magnetic eld of old neutron stars present in such systems allows the accretion disk to approach very close to the compact object, like in black hole X-ray binaries. Using data …
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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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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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Disk-magnetosphere interaction in X-ray binaries
… through the line of sight. In many systems, accretion proceeds via a Keplerian accretion disk. The differential rotation of the disk and star creates magnetic stresses that disrupt the Keplerian flow, and bring the plasma into corotation with the neutron star well above the stellar surface. …
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On the Distances and Energetics of AGN Outflows
… these outflows cannot be connected with an accretion disk surrounding the supermassive black hole as assumed in some models. Furthermore, the outflows may be out of equilibrium as we find in Mrk 509. In this case, a thorough understanding of time-dependent photoionization effects is …
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Experimental gravity with electromagnetic and gravitational waves
… the electromagnetic radiation emitted by an accretion disk around a black hole; the gravitational waves produced when comparable-mass black holes collide; and we have also studied chaotic signatures that could appear when a small compact object falls into a supermassive object during an …
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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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X-Ray studies of the physics of matter around super-massive black-holes in nearby Seyfert galaxies
… in fact, naturally emerges supposing that the accretion disk penetrates, depending to the accretion rate, the central corona at different depths (Merloni et al. 2006): the higher accreting systems hosting disks down to the last stable orbit while the lower accreting systems hosting truncated …
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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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Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks
… envelopes, bipolar outflows, and circumstellar disks, have been studied using radio interferometers: the Berkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). (1) Envelopes: Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and …
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Accretion flows and neutron star heating in low-mass X-ray binaries
… excellent test beds for studies of high-energy accretion flows and the properties of compact objects. Neutron star (NS) low-mass X-ray binaries (LMXBs) vary in brightness by almost 8 orders of magnitude and are hosts to diverse accretion flows, transporting varying amounts of energy and mass …
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Extended general relativistic magnetohydrodynamics: Formulation and application to black hole accretion
One of the long standing problems in accretion disk theory is that concerning black holes that accrete at a rate much lower than the Eddington rate. The plasma that constitutes the disk is in a regime where the Coulomb mean free path is much larger than the disk, and the collision time scales are …
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The accretion process in neutron-star low-mass X-ray binaries
… by two thermal components, i.e., a multicolor disk (MCD) and a BB, with additional weak Comp- tonized component, modeled by a single power law. I found that the accretion disk in most of the soft state is truncated at a constant value, most probably at the innermost stable circular orbit …
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Reverberation Mapping of Supermassive Black Holes using Machine Learning
… (AGN), offer a unique window into the physics of accretion and feedback that shape galactic evolution. Yet, the small spatial scales of these regions remain inaccessible to direct imaging. Reverberation mapping circumvents this limitation by using time delays between correlated emission at …
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Disk Accretion to Rotating Magnetized Stars: Magnetohydrodynamic Simulations
The star-disk interaction between a rotating magnetized star and a surrounding accretion disk is a fundamental process in astrophysics, and is usually difficult to investigate due to the complicated magnetohydrodynamic structures. The aim of this work is for understanding the accretion …
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Size is everything : universal features of quasar microlensing with extended sources
… We do this by convolving a variety of accretion disk models (including Gaussian disks, uniform disks, "cones," and a Shakura-Sunyaev thermal model) with two magnification patterns in the source plane, one with convergence [kappa] = 0.4 and shear [gamma] = 0 (positive parity), and the …
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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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Self-Similar Models of Quasar Outflow Shock Structures
… of these structures in the context of quasar accretion disk winds; we then search for the bulk acceleration (positive or negative) of low-velocity Ca II in the quasar SDSS J030000.0+004828.0 (J0300) and compare our results to model predictions. We find a strong upper limit on the acceleration …
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Black Hole Accretion Systems
"Accretion onto a black hole is the most efficient known process to convert gravitational energy into radiation. Some gamma-ray bursts (GRBs), some X-ray binaries, and all active galactic nuclei (AGN) are likely powered by accretion onto a rotating black hole. I model the global, timedependent …
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