Spectra and Variability of Black Hole Accretion Disk Models Built on Magnetorotational Turbulence

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

AST-0707624 Blaes Accretion disk theory has been undergoing a slow but steady revolution ever since the discovery that turbulence driven by the magnetorotational instability (MRI) is likely to be responsible for outward angular momentum transport. Thanks in large part to simulations of MRI turbulence, scientists are for the first time getting a handle on the true vertical structure of accretion disks, free of ad hoc assumptions. This project will analyze new simulations with radiation pressure much larger than gas pressure. This radiation pressure-dominated regime is the most uncertain and at the same time the most important for understanding the innermost regions of luminous accretion disks around black holes. The study will also rebuild spectral models of accretion disks, applicable to both stellar mass black hole X-ray binaries and supermassive black holes in quasars and active galactic nuclei. The techniques include Monte Carlo methods to handle radiative transfer. In further activity, the group will analyze local and global MRI simulations, perform analytic calculations of linear modes and nonlinear driving and damping, and simulate linear instabilities in magnetically dominated configurations. The end result will be a complete understanding of the true vertical structure of accretion disks around black holes in all regimes, from the gas pressure dominated outer regions to the radiation pressure dominated inner regions. The spectral models will be fully predictive for the first time, as they are based on physics and not ad hoc assumptions. This research will lead to a deep understanding of the expected variability of MRI flow structures based on combining analytic and quasi-analytic linear mode theory and local and global simulations. The project will be the main vehicle for the theses of two graduate students, one concentrating on numerical simulations, and the other focused mainly on analytic calculations and numerical spectral modeling. The researchers will also continue to engage the public in exciting developments in black hole astrophysics, using movies and images from numerical simulations as well as music-based ideas to explain black hole X-ray variability.