The Disk Accretion Rate for Dynamo-generated Turbulence

Abstract

Dynamo-generated turbulence is simulated in a modified shearing box approximation that removes scale invariance and allows finite accretion rates for a given distance from the central object. The effective Shakura-Sunyaev viscosity parameter, ff SS , is estimated in three different ways using the resulting mass accretion rate, the heating rate, and the horizontal components of the Maxwell and Reynolds stress tensors. The results are still resolution dependent: doubling the resolution leads to 1.4-1.6 times larger values for the viscosity parameter. For 63 \\Theta 127 \\Theta 64 meshpoints we find that ff SS = 0:007. Subject headings: accretion: accretion disks -- hydrodynamics -- MHD -- turbulence -- 3 -- 1. Introduction Over the last few years it has become clear that a strong candidate for the origin of turbulence in accretion disks is the magnetic shear instability, often called the BalbusHawley (1991) instability. In its original form, the instability arises in the presence of a ve...