Efficient highly-subsonic turbulent dynamo and growth of primordial magnetic fields

TL;DR

This study investigates how turbulent dynamo processes amplify magnetic fields in highly subsonic regimes, revealing increased efficiency at lower Mach numbers and implications for primordial magnetic field strengths in the early Universe.

Contribution

First analysis of magnetic field amplification by turbulent dynamo in highly subsonic conditions, with predictions for primordial magnetic field strengths.

Findings

Dynamo saturation efficiency increases as Mach number decreases.

Magnetic fields can reach >10^{-16} G on 0.1 pc scales.

Fields compatible with intergalactic magnetic field limits.

Abstract

We present the first study on the amplification of magnetic fields by the turbulent dynamo in the highly subsonic regime, with Mach numbers ranging from $10^{-3}$ to $0.4$. We find that for the lower Mach numbers the saturation efficiency of the dynamo, $(E_{\mathrm{mag}}/E_{\mathrm{kin}})_{\mathrm{sat}}$, increases as the Mach number decreases. Even in the case when injection of energy is purely through longitudinal forcing modes, $(E_{\mathrm{mag}}/E_{\mathrm{kin}})_{\mathrm{sat}}$ $\gtrsim 10^{-2}$ at a Mach number of $10^{-3}$. We apply our results to magnetic field amplification in the early Universe and predict that a turbulent dynamo can amplify primordial magnetic fields to $\gtrsim$ $10^{-16}$ Gauss on scales up to 0.1 pc and $\gtrsim$ $10^{-13}$ Gauss on scales up to 100 pc. This produces fields compatible with lower limits of the intergalactic magnetic field inferred from blazar $\gamma$-ray observations.