1992/10/30 by Ethan T. Vishniac, Vishniac, Ethan T.
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9210006
20 pages
arxiv created 1992/10/30 · arxiv updated 2009/12/01
The galactic magnetic field is commonly supposed to be due to a dynamo acting on some large scale seed field. A major difficulty with this idea is that estimates of reasonable seed field strengths tend to be quite low, on the order of ∼10-20 gauss. Here we examine the contribution due to the flux entrained in winds from protostars formed in the first dynamo e-folding time of a galaxy's existence. Using a minimal estimate of a protostellar magnetic field we find that if each protostar ejects a single current ring, sufficient to maintain flux freezing in the wind, than the large scale average dipole field from all such current rings will be at least 5 orders of magnitude larger than previous seed field estimates. Allowing for a reasonable amount of magnetic activity in protostars during an extended period of mass loss increases this to a dipole seed field of ∼10-12 gauss. For the purposes of producing a seed field it is irrelevant whether or not this initial injection of flux takes place in a newly formed galactic disk, or in star forming proto-galactic clouds. The compression of this dipole field into a thin disk will lead to a large scale Br∼ 10-10.5 gauss. Initially, field strengths on smaller scales will be larger, but nowhere near current levels.