Non-Gaussian Magnetic Structures in the Small-Scale Turbulent Dynamo

TL;DR

This study uses 3D turbulence simulations to analyze the complex, non-Gaussian magnetic structures produced by the small-scale turbulent dynamo across different Mach numbers, revealing morphological differences between growth stages.

Contribution

It provides a quantitative framework for understanding magnetic field morphology evolution and the impact of turbulence compressibility on magnetic structures.

Findings

Magnetic fields significantly deviate from Gaussian randomness.

Magnetic structures are less curved and more interconnected in the saturated stage.

Morphological differences decrease with increasing compressibility.

Abstract

The small-scale turbulent dynamo is a key mechanism for amplifying galactic magnetic fields, yet the resulting field morphology remains poorly understood. Using 3D driven turbulence simulations across a range of compressibilities, characterised by Mach number, and Minkowski functionals, we quantitatively investigate the morphology of magnetic fields generated by the small-scale turbulent dynamo in both the exponentially growing kinematic stage and the statistically steady saturated stage. In both stages and across all Mach numbers, we find that the magnetic field departs significantly from a Gaussian random field. Magnetic structures are statistically less curved and more interconnected in the saturated stage than in the kinematic stage, with these morphological differences decreasing as compressibility increases. Our work provides a quantitative description of how density fluctuations in turbulence and the back-reaction of amplified magnetic fields via the Lorentz force together shape complex, non-Gaussian magnetic structures, and offers a valuable framework for comparing simulations with both analytical models and polarisation observations.