Magnetized Gas Clouds can Survive Acceleration by a Hot Wind

TL;DR

This study uses 3D magnetohydrodynamic simulations to show that magnetic fields help gas clouds survive acceleration by hot winds, explaining observed cool gas in galactic environments and predicting orbital deviations for the G2 cloud.

Contribution

It demonstrates how internal magnetic fields in gas clouds suppress disruption and enhance drag forces, providing new insights into cloud survival in hot astrophysical winds.

Findings

Magnetic fields suppress cloud disruption and mixing.

Magnetic fields increase drag force on clouds.

Predicted orbital deviation for the G2 cloud in the galactic center.

Abstract

We present three-dimensional magnetohydrodynamic simulations of magnetized gas clouds accelerated by hot winds. We initialize gas clouds with tangled internal magnetic fields and show that this field suppresses the disruption of the cloud: rather than mixing into the hot wind as found in hydrodynamic simulations, cloud fragments end up co-moving and in pressure equilibrium with their surroundings. We also show that a magnetic field in the hot wind enhances the drag force on the cloud by a factor ~(1+v_A^2/v_wind^2)$, where v_A is the Alfven speed in the wind and v_wind measures the relative speed between the cloud and the wind. We apply this result to gas clouds in several astrophysical contexts, including galaxy clusters, galactic winds, the Galactic center, and the outskirts of the Galactic halo. Our results can explain the prevalence of cool gas in galactic winds and galactic halos and how such cool gas survives in spite of its interaction with hot wind/halo gas. We also predict that drag forces can lead to a deviation from Keplerian orbits for the G2 cloud in the galactic center.