Turbulence and Magnetic Field Amplification in Supernova Remnants: Interactions Between A Strong Shock Wave and Multi-Phase Interstellar Medium

TL;DR

This study uses MHD simulations to show how strong shock waves in the interstellar medium can generate turbulence and amplify magnetic fields up to milligauss levels, explaining observed features in supernova remnants.

Contribution

It demonstrates that shock interactions with a two-phase interstellar medium naturally lead to magnetic field amplification and turbulence, aligning with recent observations of supernova remnants.

Findings

Magnetic fields can be amplified to ~1 mG in shock-compressed shells.

Turbulent regions with strong magnetic fields are spatially localized (~0.05 pc).

Simulated magnetic structures resemble observed X-ray hot spots in supernova remnants.

Abstract

We examine MHD simulations of the propagation of a strong shock wave through the interstellar two-phase medium composed of small-scale cloudlets and diffuse warm neutral medium in two-dimensional geometry. The pre-shock two-phase medium is provided as a natural consequence of the thermal instability that is expected to be ubiquitous in the interstellar medium. We show that the shock-compressed shell becomes turbulent owing to the preshock density inhomogeneity and magnetic field amplification takes place in the shell. The maximum field strength is determined by the condition that plasma beta ~ 1, which gives the field strength on the order of 1 mG in the case of shock velocity ~ 1,000 km/s. The strongly magnetized region shows filamentary and knot-like structures in two-dimensional simulations. The spatial scale of the regions with magnetic field of 1 mG in our simulation is roughly 0.05 pc which is comparable to the spatial scale of the X-ray hot spots recently discovered in supernova remnants where the magnetic field strength is indicated to be amplified up to the order of 1 mG. This result may also suggest that the turbulent region with locally strong magnetic field is expected to be spread out in the region with frequent supernova explosions, such as in the Galactic center and starburst galaxies.