On the Rayleigh–Taylor Instability of Radio Bubbles in Galaxy Clusters

We consider the Rayleigh–Taylor instability in the early evolution of the rarefied radio bubbles (cavities) observed in many cooling–flow clusters of galaxies. The top of a bubble becomes prone to the Rayleigh–Taylor instability as the bubble rises through the intra–cluster medium (ICM). We show that while the jet is powering the inflation, the deceleration of the bubble–ICM interface is able to reverse the Rayleigh–Taylor instability criterion. In addition, the inflation introduces a drag effect which increases substantially the instability growth time. The combined action of these two effects considerably delays the onset of the instability. Later on, when the magnitude of the deceleration drops or the jet fades, the Rayleigh–Taylor and the Kelvin–Helmholtz instabilities set in and eventually disrupt the bubble. We conclude that the initial deceleration and drag, albeit unable to prevent the disruption of a bubble, may significantly lengthen its lifetime, removing the need to invoke stabilising magnetic fields.