Numerical Simulations of a Shock Interacting with Multiple Magnetized Clouds

TL;DR

This study uses 2D MHD simulations to analyze how shocks interact with multiple magnetized clouds, revealing complex behaviors influenced by magnetic fields and cloud positioning, relevant to astrophysical phenomena like supernova remnants.

Contribution

First detailed 2D MHD simulations of shock interactions with multiple magnetized clouds, exploring effects of cloud positioning and magnetic field orientation on cloud dynamics.

Findings

Clouds are stretched or confined along magnetic field lines.

Upstream clouds can accelerate past downstream clouds.

Cloud interactions affect compression cycles and plasma beta values.

Abstract

We present 2D adiabatic magnetohydrodynamic (MHD) simulations of a shock interacting with groups of two or three cylindrical clouds. We study how the presence of a nearby cloud influences the dynamics of this interaction, and explore the resulting differences and similarities in the evolution of each cloud. The understanding gained from this small-scale study will help to interpret the behaviour of systems with many 10's or 100's of clouds. We observe a wide variety of behaviour in the interactions studied, which is dependent on the initial positions of the clouds and the orientation and strength of the magnetic field. We find: i) some clouds are stretched along their field-lines, whereas others are confined by their field-lines; ii) upstream clouds may accelerate past downstream clouds (though magnetic tension can prevent this); iii) clouds may also change their relative positions transverse to the direction of shock propagation as they "slingshot" past each other; iv) downstream clouds may be offered some protection from the oncoming flow as a result of being in the lee of an upstream cloud; v) the cycle of cloud compression and re-expansion is generally weaker when there are nearby neighbouring clouds; vi) the plasma $\beta$ in cloud material can vary rapidly as clouds collide with one another, but low values of $\beta$ are always transitory. This work is relevant to studies of multi-phase regions, where fast, low-density gas interacts with dense clouds, such as in circumstellar bubbles, supernova remnants, superbubbles and galactic winds.