The Galactic Dynamo and Superbubbles

Russell M. Kulsrud

Published 2015-02-05Version 1

A novel idea is presented for removing mag- netic flux from the galactic disc in order to satisfy the boundary conditions of the alpha- omega dynamo. The idea involves making use of superbubbles that break out of the galactic disc. When this happens, their shells break up into many fragments, and from these fragments, spikes can arise that can move small pieces of the galactic flux lines in the superbubble shell and move them so high enough into the halo that they do not return. As a result the flux lines remaining in the disc are effectively cut into short pieces of finite length that, although weakly connected to the halo, have no tensile strength at their ends. They are thus free to randomly rotate until no net flux is left. In the first section, the boundary condition problem is discussed and then this solution is discussed.. In the second section the proper- ties of the superbubble that are necessary for the model are laid out. It is shown by a rough numerical estimate, that enough lines can be cut to resolve the dynamo problem. Lastly, conditions under which the spike instability exists are discussed.