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On the Origin of the Galactic Magnetic Field | | Ethan T. Vishniac
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30 Oct 1992 | | Subject: | astro-ph | | Abstract: | 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 $sim10^{-20}$ 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 $sim10^{-12}$ 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 $B_rsim 10^{-10.5}$ gauss. Initially, field strengths on smaller scales will be larger, but nowhere near current levels. | | Source: | arXiv, astro-ph/9210006 | | Services: | Forum | Review | PDF | Favorites | |
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