Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21732201s&link_type=abstract
American Astronomical Society, AAS Meeting #217, #322.01; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astrophysics
Scientific paper
The most promising candidate for angular momentum transport in accretion disks is magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI). Most numerical simulations of MRI-driven turbulence are performed in the local, unstratified approximation: a small, co-rotating patch of accretion disk is evolved and the vertical component of gravity is ignored. Recently, these simulations have shown that turbulence levels increase with the ratio of the gas shear viscosity to Ohmic resistivity, i.e., the magnetic Prandtl number. Here, I present a series of local simulations that include vertical gravity in order to further investigate the Prandtl number effect in a more astrophysically relevant context. These calculations show that for moderate resistivities, the MRI saturation level exhibits a very strong temporal variability; the turbulence episodically transitions between "high" and "low" states on timescales of 100 local orbits. This behavior is directly linked to a dynamo mechanism present in vertically stratified local simulations and may have relevance for accretion variability in partially ionized disks, such as dwarf novae and protoplanetary disks.
Beckwith Kris
Hawley John F.
Simon Jacob B.
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