The small-scale turbulent dynamo in smoothed particle magnetohydrodynamics

TL;DR

This study uses advanced smoothed particle magnetohydrodynamics simulations to investigate the small-scale dynamo process in supersonic turbulence, relevant to star formation, demonstrating magnetic field amplification and agreement with grid-based methods.

Contribution

It introduces a new divergence cleaning algorithm and numerical techniques for SPMHD, enabling accurate simulation of magnetic field amplification in turbulent astrophysical environments.

Findings

Magnetic energy grows over 10 orders of magnitude to saturation.

Results agree well with grid-based simulation methods.

New divergence cleaning method achieves machine-precision divergence-free magnetic fields.

Abstract

Supersonic turbulence is believed to be at the heart of star formation. We have performed smoothed particle magnetohydrodynamics (SPMHD) simulations of the small-scale dynamo amplification of magnetic fields in supersonic turbulence. The calculations use isothermal gas driven at rms velocity of Mach 10 so that conditions are representative of star-forming molecular clouds in the Milky Way. The growth of magnetic energy is followed for 10 orders in magnitude until it reaches saturation, a few percent of the kinetic energy. The results of our dynamo calculations are compared with results from grid-based methods, finding excellent agreement on their statistics and their qualitative behaviour. The simulations utilise the latest algorithmic developments we have developed, in particular, a new divergence cleaning approach to maintain the solenoidal constraint on the magnetic field and a method to reduce the numerical dissipation of the magnetic shock capturing scheme. We demonstrate that our divergence cleaning method may be used to achieve $\nabla \cdot {\bf B}=0$ to machine precision, albeit at significant computational expense.