Rayleigh-Taylor instability and mixing in SN 1987A

We investigate the stability of the supernova ejecta against the Rayleigh-Taylor instability for the realistic model SN 1987A. A linear analysis indicates that the layers around the composition interface between the hydrogen-rich and helium zones and that between the helium and metal zones become Rayleigh-Taylor unstable. In these layers, the pressure increases outward because of deceleration due to the reverse shock which forms when the blast shock hits the massive hydrogen-rich envelope. On the contrary, the density steeply decreases outward because of the preexisting nuclear burning shell. Then the layers undergo the Rayleigh-Taylor instability because of the opposite signs of the pressure and density gradients. The estimated growth rate is larger than the expansion rate of the supernova. The Rayleigh-Taylor instability near the composition interface is likely to induce the mixing which has been strongly suggested from observations of SN 1987A.