The Small-Scale Dynamo and Non-Ideal MHD in Primordial Star Formation

TL;DR

This paper investigates how turbulence during primordial star formation amplifies magnetic fields via the small-scale dynamo, considering non-ideal MHD effects, and explores their potential impact on early cosmic structure formation.

Contribution

It applies Kazantsev theory with detailed chemistry and non-ideal MHD effects to model magnetic field amplification in primordial halos, highlighting the rapid saturation of magnetic fields.

Findings

Magnetic fields can be amplified efficiently during primordial halo formation.

Saturation of magnetic fields occurs within a small density range for various turbulence types.

Generated magnetic fields may influence early star and galaxy formation processes.

Abstract

We study the amplification of magnetic fields during the formation of primordial halos. The turbulence generated by gravitational infall motions during the formation of the first stars and galaxies can amplify magnetic fields very efficiently and on short timescales up to dynamically significant values. Using the Kazantsev theory, which describes the so-called small-scale dynamo - a magnetohydrodynamical process converting kinetic energy from turbulence into magnetic energy - we can then calculate the growth rate of the small-scale magnetic field. Our calculations are based on a detailed chemical network and we include non-ideal magnetohydrodynamical effects such as ambipolar diffusion and Ohmic dissipation. We follow the evolution of the magnetic field up to larger scales until saturation occurs on the Jeans scale. Assuming a weak magnetic seed field generated by the Biermann battery process, both Burgers and Kolmogorov turbulence lead to saturation within a rather small density range. Such fields are likely to become relevant after the formation of a protostellar disk and, thus, could influence the formation of the first stars and galaxies in the Universe.