Generation of a seed magnetic field around first stars: The Biermann battery effect

Abstract

We investigate the generation processes of magnetic fields around first stars. Since first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magnetic fields are generated by the effects of radiation force, as well as the Biermann battery effect. We calculated the amplitude of the magnetic field generated by the effects of radiation force around the first stars in a preceding paper but the Biermann battery effects were not taken into account. In this paper, we calculate the generation of magnetic fields by the Biermann battery effect as well as the effects of radiation force, utilizing radiation hydrodynamics simulations. As a result, we find that the generated magnetic field strengths are ∼10-19 G - 10-17 G at ∼100 pc-1 kpc scale, an order of magnitude larger than the results of our previous study mainly as a result of the Biermann battery effect. We also find that this result is insensitive to various physical parameters including the mass of the source star and the distance between the source and the dense clump, unless we take unlikely values of these parameters. © 2011. The American Astronomical Society. All rights reserved.