Animations of the decay of a poloidal magnetic field in non-rotating and rotating star The animations below show the strength of the radial component of the magnetic field on the surface of a star, as measured in simulations. (The x- and y-axes correspond to longitude and latitude.) Left, the non-rotating case, and right, the star is rotating such that the rotation velocity is ten times the magnetic (Alfven) velocity. It is clear that the rotation does somehow restrict the growth of the instability, although the magnetic energy is still lost relatively quickly. Therefore, it does seem very likely that a stable field in a rotating star will need to be of a mixed poloidal-toroidal form.


Below are two more animations of the same two simulations. Click on the pictures to see the animations. The blue sphere represents the star and the lines represent the field lines, with yellow meaning strong magnetic field and red meaning weak. In the non-rotating case on the left, we start with an equilibrium (the movement visible in the animation is just sound waves) and after some time, the instability becomes visible in the equatorial region, quickly spreading to the rest of the star. At the end of the simulation, the original field has been almost completely destroyed. In the rotating case, on the right, we see that the growth of the instability is restricted in the non-linear phase and that the overall dipole field decays more slowly.


Please let me know if you have any problems downloading these two animations.

Back to research interests
Back to main page