Effect of liquid density on the Rayleigh-Taylor instability of sonoluminescing bubbles

Rayleigh-Taylor instability of a radially oscillating gas bubble immersed in water is numerically studied. The model includes density changes in both gas within the bubble and liquid around its wall. The radial dynamics is described by Gilmore equation, which is coupled with the van der Waals (gas) and Tait (liquid) equations of state for simulating density variations. Shape instability is analyzed by the classical Hill's equation, which describes the time evolution of the distortion amplitude. During the last moments of collapse, a sudden rise in gas and liquid densities is predicted; this exerts a stabilizing effect on the Rayleigh-Taylor instability. An instability borderline set by a new overwhelming criterion is in good agreement with an experimental boundary.