Small-scale turbulent dynamo in astrophysical environments: nonlinear dynamo and dynamo in a partially ionized plasma

TL;DR

This paper reviews recent advances in understanding small-scale turbulent dynamo processes in astrophysical environments, focusing on nonlinear regimes and partially ionized plasmas, with analytical and numerical insights and astrophysical applications.

Contribution

It introduces new theories for the nonlinear dynamo in partially ionized plasmas and presents numerical simulations validating these theories, highlighting the role of reconnection diffusion and ion-neutral interactions.

Findings

Reconnection diffusion significantly influences magnetic field amplification.

Ion-neutral coupling affects dynamo efficiency and magnetic structures.

Numerical simulations support analytical predictions of dynamo behavior.

Abstract

Small-scale turbulent dynamo is responsible for the amplification of magnetic fields on scales smaller than the driving scale of turbulence in diverse astrophysical media. Most earlier dynamo theories concern the kinematic regime and small-scale magnetic field amplification. Here we review our recent progress in developing the theories for the nonlinear dynamo and the dynamo regime in a partially ionized plasma. The importance of reconnection diffusion of magnetic fields is identified for both the nonlinear dynamo and magnetic field amplification during gravitational contraction. For the dynamo in a partially ionized plasma, the coupling state between neutrals and ions and the ion-neutral collisional damping can significantly affect the dynamo behavior and the resulting magnetic field structure. We present both our analytical predictions and numerical tests with a two-fluid dynamo simulation on the dynamo features in this regime. In addition, to illustrate the astrophysical implications, we discuss several examples for the applications of the dynamo theory to studying magnetic field evolution in both preshock and postshock regions of supernova remnants, in weakly magnetized molecular clouds, during the (primordial) star formation, and during the first galaxy formation.