Radiation/MHD Simulations of Accretion
Abstract
Radiation is a critical constituent of the dynamics of accretion into deep gravitational potentials both because cooling losses define the matter's equation of state and because, in many circumstances, radiation forces dominate the matter's internal structure. Previous studies of these effects have been restricted to cases of special symmetry by the limitations of their algorithms for computing radiation transfer. We have developed new algorithms for combining accurate solution of the time-dependent 3-d radiation transfer problem with intrinsically conservative time-advance of the 3-d MHD dynamical equations. We propose to implement these methods in numerical simulation codes suitable for studying astrophysical accretion and then apply them to several major problems in accretion physics. First, earlier work has suggested that radiation-dominated disks may be subject to inflow instabilities; our new techniques will be able to test whether these fluctuations actually grow, and if so, what ultimate state the accretion disk reaches. Our results will have direct implications for both the emitted spectra and fluctuation power spectra of a wide range of accreting objects. Second, we will explore how realistic equations of state affect the global structure and emitted spectra of accretion disks. Third, we will explore the dynamics of mass accretion at such a large rate that, if light were generated with the usual relativistic efficiency, the luminosity would exceed the Eddington limit and outward radiation forces would overwhelm gravity. All previous discussions of this problem have rested on phenomenological scaling arguments and rough approximations; ours will be the first to examine it on the basis of genuine physical mechanisms evaluated quantitatively. We aim to clarify the nature of super-Eddington accretion in objects ranging from Galactic black hole binaries to extragalactic Ultra-Luminous X-ray sources to AGN. These issues affect at a fundamental level how black holes grow and emit light from their immediate environs, so our results will have direct and deep consequences for our understanding of both their evolution and their observational properties. Because black holes are the observing targets of numerous NASA astrophysics missions, we expect our work to yield important advances in the interpretation of their data.
- Publication:
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NASA ATP Proposal
- Pub Date:
- 2010
- Bibcode:
- 2010atp..prop...27K