Is the Oort AValue a Universal Growth Rate Limit for Accretion Disk Shear Instabilities?
Abstract
A weakfield local MHD instability that is of importance to accretion disks is examined. The maximum growth rate of the instability is found to be not only independent of the magnetic field strength but independent of field geometry as well. In particular, all Keplerian disks are unstable in the presence of any weak poloidal field, with the ratio of the maximum growth rate to disk angular velocity given by 3/4. The maximum growth rate of any weak field configuration that is not purely toroidal is given by the local Oort Avalue of the disk. The behavior is studied by using a form of the dynamical Hill equations. It is conjectured that the Oort Avalue is an upper bound to the growth rate of any instability feeding upon the free energy of differential rotation.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 1992
 DOI:
 10.1086/171467
 Bibcode:
 1992ApJ...392..662B
 Keywords:

 Accretion Disks;
 Hill Method;
 Magnetic Field Configurations;
 Magnetohydrodynamic Stability;
 Computer Graphics;
 Oort Cloud;
 Astrophysics;
 ACCRETION;
 ACCRETION DISKS;
 INSTABILITIES;
 MAGNETOHYDRODYNAMICS: MHD