The Age Evolution of the Radio Morphology of Supernova Remnants

TL;DR

This study analyzes how supernova remnants' radio morphologies evolve with age, revealing that older remnants tend to be more elongated and asymmetric due to interactions with a turbulent interstellar medium.

Contribution

It provides the first large-scale observational evidence linking SNR asymmetry growth to age and environmental inhomogeneities, supporting hydrodynamical models.

Findings

Older SNRs are more elliptical and asymmetric.

Asymmetry increases with SNR size and age.

Results support models of SNR expansion in turbulent ISM.

Abstract

Recent hydrodynamical models of supernova remnants (SNRs) demonstrate that their evolution depends heavily on the inhomogeneities of the surrounding medium. As SNRs expand, their morphologies are influenced by the non-uniform and turbulent structure of their environments, as reflected in their radio continuum emission. In this paper, we measure the asymmetries of 96 SNRs in radio continuum images from three surveys of the Galactic plane and compare these results to the SNRs' radii, which we use as a proxy for their age. We find that larger (older) SNRs are more elliptical/elongated and more mirror asymmetric than smaller (younger) SNRs, though the latter vary in their degrees of asymmetry. This result suggests that SNR shells become more asymmetric as they sweep up the interstellar medium (ISM), as predicted in hydrodynamical models of SNRs expanding in a multi-phase or turbulent ISM.