Physics and Astronomy
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Browsing Physics and Astronomy by Subject "Accretion disks"
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Item Open Access Self-Similar Models of Quasar Outflow Shock Structures(2024-03-16) Weiss, Erik Adam; Hall, Patrick B.Supersonic winds of outflowing material are observed and/or predicted in a number of astrophysical systems; such winds may drive an expanding shock structure that shocks and pushes the ambient interstellar medium (ISM) outward. This thesis analyses, combines and expands on existing analytic self-similar models 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 magnitude, yielding plausible model constraints, but the observed range of gas velocities implies that the Ca II velocity profile does not coincide with that of the shocked ISM. We conclude with a discussion of recent results regarding J0300's outflow properties and briefly investigate the possibility of pre-existing ISM cloud disruption as an explanation for the observed Ca II velocity profile.Item Open Access Stars Versus Quasar Accretion Disks(2023-08-04) Seaton, Lucas Matthew; Hall, Patrick B.This thesis investigates the astrophysical effects of stars colliding with the accretion disks of supermassive black holes (SMBH) in active galactic nuclei (AGN). In this work, we model the AGN to have a thin accretion disk surrounded by a stellar nuclear cluster (SNC) containing stars on various orbital eccentricities and inclination angles striking the disk at periapse. An impacting star carves a tilted cylindrical tunnel out of the disk material and loses up to $6\times10^{-4}\%$ of its stellar mass. The time-averaged collisional luminosity is at most $10^{-2}$ times the entire disk's expected luminosity, while the emission profile of an impact site initially flares before quickly dimming to the brightness of the local disk. The parameters of the SMBH, accretion disk, SNC, and impacting stars are altered to reveal that star-disk collisions from a densely populated SNC can outshine the disk luminosity.