  Recent Chandra and XMM-Newton observations of galaxy cluster cooling flows
have revealed X-ray emission voids of up to 30 kpc in size that have been
identified with buoyant, magnetized bubbles. Motivated by these observations,
we have investigated the behavior of rising bubbles in stratified atmospheres
using the FLASH adaptive-mesh simulation code. We present results from 2-D
simulations with and without the effects of magnetic fields, and with varying
bubble sizes and background stratifications. We find purely hydrodynamic
bubbles to be unstable; a dynamically important magnetic field is required to
maintain a bubble's integrity. This suggests that, even absent thermal
conduction, for bubbles to be persistent enough to be regularly observed, they
must be supported in large part by magnetic fields. Thermal conduction
unmitigated by magnetic fields can dissipate the bubbles even faster. We also
observe that the bubbles leave a tail as they rise; the structure of these
tails can indicate the history of the dynamics of the rising bubble.
