Long-Term Evolution of Magnetized Bubbles in Galaxy Clusters

An unsolved problem in active galactic nuclei (AGN) feedback on clusters is how to account for the the morphology and stability of buoyant bubbles and their interactions with the ambient intracluster medium (ICM). Appreciable magnetic energy has been observed in both cluster and radio lobe plasmas. We have performed nonlinear ideal magnetohydrodynamic simulations of the long term evolution of a magnetized low-density ``bubble'' plasma formed by a radio galaxy in a stratified cluster medium. It is found that about 3.5\% of the initial magnetic energy remains in the bubble after $\sim 8 \times 10^{9}$~years, and the initial magnetic bubble expansion is adiabatic. The bubble can survive for at least $8\times 10^9$~years due to the stabilizing effect of the bubble magnetic field on Rayleigh-Taylor and Kelvin-Holmholtz instabilities, possibly accounting for ``ghost cavities" as observed in Perseus-A. A filament structure spanning about 500~kpc is formed along the path of bubble motion. The mean value of the magnetic field inside this structure is $\sim 0.88$~$\mu$G at $\sim8\times10^9$~years. Finally, the initial bubble momentum and rotation have limited influence on the long term evolution of the bubble.