Dynamics and stability of magnetized AGN-blown bubbles in clusters of galaxies

TL;DR

This study uses MHD simulations to show that magnetized AGN-blown bubbles in galaxy clusters are stabilized against instabilities, explaining their observed long-term coherence and potential role in cluster heating.

Contribution

The paper demonstrates that large-scale magnetic fields stabilize AGN bubbles, allowing them to remain coherent and effectively heat cluster cores, which is a new insight into their dynamics.

Findings

Magnetic fields stabilize bubbles against fluid instabilities.

Bubbles remain coherent over long timescales in simulations.

Bubbles dissipate energy efficiently, aiding cluster heating.

Abstract

We perform MHD simulations of AGN-blown bubbles in the Intercluster Medium (ICM) containing large-scale coherent magnetic fields. We assume that bubbles, created by the intermittent jets from Active Galactic Nuclei, quickly relax to the Woltjer-Taylor spheromak-like state, with internal plasma beta-parameter $\sim 1$. We demonstrate that such bubbles rising through hydrostatically-stratified atmosphere are magnetically stabilized against fluid interface instabilities, remaining coherent for a long time. Typical velocity is $ v /c_s \sim \sqrt{R/H} \leq 1 $ ($c_s$ is sound speed, $R$ is the bubble size, $H$ is the scale height). Current-driven instabilities (internal kinks) lead to bubble's tilting, but develop on long time scales, and remain unimportant, leading to minor modifications of the internal structure. Our results explain apparent long-term stability of ICM cavities. Subsonically rising stable bubbles dissipate in their wake approximately the energy initially injected by the jet, and may efficiently reheat the clusters cores in a ``gentle'' way.