Long Term Evolution of Magnetized Bubbles in Galaxy Clusters

We have performed nonlinear ideal MHD 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 8 billion years, and the initial magnetic bubble expansion is adiabatic. The bubble can survive for at least 8 billion 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 0.88 micro Gauss at 8 billion years. Finally, the initial bubble momentum and rotation have limited influence on the long term evolution of the bubble.