Physical and numerical instabilities of radiatively cooling shocks in turbulent magnetized media

Abstract

ABSTRACT We consider the influence of a fluctuating magnetic field on to the structure formation and instabilities of radiatively cooling blast waves. The study is based on an example of optically thin post-adiabatic supernova remnants (SNRs) in the homogeneous interstellar medium. By means of analytic estimations and full-scale multidimensional simulations, we investigate the roles of thermal, hydrodynamic (corrugation, pulsational, convective, Rayleigh–Taylor, linear and non-linear Vishniac) and numerical instabilities (‘carbuncle’ and grid-forced effects). It is found that of primary importance is the interplay of the thermal instability with quasi-regular and random components of the interstellar field. Bending fluctuations caused by the latter can be strongly amplified by non-linear Vishniac instability in the SNR regions where the regular component is almost normal to the shock. The instabilities driven by counter-directional pressure and density gradients are limited mostly to very narrow post-shock cooling layers, transient perturbations of the same short scales, and rather weakly magnetized environments. Some of these results can also be applied to radiative shocks separating optically thick media from thin or semitransparent ones. Several recommendations and requirements on numerical simulation techniques are formulated.