Black Hole Accretion Dynamics in Numerical Simulations
Author | : Kenneth B. Henisey |
Publisher | : |
Total Pages | : 70 |
Release | : 2011 |
Genre | : |
ISBN | : 9781267020055 |
Download Black Hole Accretion Dynamics in Numerical Simulations Book in PDF, Epub and Kindle
Light curves from accreting black hole systems exhibit variability which has neither been conclusively explained by analytic models nor seen in numerical simulations of these flows. Until recently, these computational studies have uniformly assumed alignment between the angular momenta of a black hole and its accretion disk. In contrast, observational data suggests that these tilted configurations may exist in real astrophysical systems and theoretical work indicates that tilt is accompanied by disk eccentricity and warp capable of exciting trapped diskoseismological modes. This dissertation analyzes the spatial and temporal behavior of fluid in fully three-dimensional, general relativistic, magnetohydrodynamical simulations, the first of their kind, of both tilted and untilted black hole accretion flows. We uncover characteristically greater variability in tilted simulations at frequencies similar to those predicted by the formalism of trapped modes, but ultimately conclude that its spatial structure is inconsistent with a modal interpretation. We find instead that over-dense clumps orbiting on roughly Keplerian trajectories appear generically in our global simulations independent of tilt and that these blobs give rise to acoustic wakes inside and outside of their corotation radius. Our three dimensional analysis of the flow yields two additional results. First, we confirm the strongly asymmetric nature of the tilted configuration by further describing two previously identified standing shock structures in the background flow; second, we show that these shocks effectively amplify the blob-wake variability and thus explain the increased variability observed in our tilted datasets. Our identification of clumps, wakes, and wake-shock interactions in these tilted, fully general relativistic, magnetohydrodynamical simulations will certainly be relevant to those models which incorporate tilt as a way to explain the observed variability in black hole accretion flow.