Magnetic fields and differential rotation in stars

Abstract

In a star with a magnetic field that is not symmetric about the rotation axis, non-uniform rotation in the electrically conducting stellar material shears the field and generates magnetic torques. This leads to a competition between the efforts of the magnetic stresses to remove non-uniformities in angular velocity, and those of the velocity field to bury and destroy magnetic flux. Illustrative calculations are presented for a compressible model in an idealized two-dimensional geometry. They show how, with values of diffusion coefficients appropriate to a radiative envelope, the Lorentz stresses can rapidly establish a state of approximately uniform rotation for relatively modest fields strenghts