Generation of Seed Magnetic Field around First Stars: the Biermann Battery Effect

TL;DR

This study models magnetic field generation around first stars, highlighting the Biermann battery effect's significant role and its relative insensitivity to various physical parameters.

Contribution

It quantitatively demonstrates the Biermann battery effect's importance in magnetic field generation around first stars using radiation hydrodynamics simulations.

Findings

Magnetic fields of ~10^{-19}G to 10^{-17}G are generated at 100pc-1kpc scales mainly by the Biermann battery.

The results are robust against variations in source star mass and distance, unless extreme values are used.

The magnetic field strength is an order of magnitude larger than previous estimates that excluded the Biermann effect.

Abstract

We investigate generation processes of magnetic fields around first stars. Since the first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magnetic fields are generated by effects of radiation force as well as the Biermann battery effect. We have calculated the amplitude of magnetic field generated by the effects of radiation force around the first stars in the preceding paper, in which the Biermann battery effects are 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 the radiation hydrodynamics simulations. As a result, we find that the generated magnetic field strengths are ~ 10^{-19}G-10^{-17}G at ~ 100pc-1kpc scale mainly by the Biermann battery, which is an order of magnitude larger than the results of our previous study. We also find that this result is insensitive to various physical parameters including the mass of the source star, distance between the source and the dense clump, unless we take unlikely values of these parameters.