Numerical simulation of mixing in supernova ejecta

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Observations of SN 1987A strongly suggest the occurrence of large scale mixing during the explosion. The most promising mechanism to mix the ejecta is the Rayleigh-Taylor(R-T)instability so that we have numerically follow a nonlinear growth of the R-T instability using a much more refined two-dimensional(2-D)axisymmetric hydrodynamic code than in our previous work. The growth of the R-T instability depends strongly on the amplitude of the initial perturbation. It is found that the instabilities grow considerably even if we perturb the velocity field by 1%. The HE/C+O interface is not so unstable while the instability is pronounced at the H/He interface. Eventually the core material(inside the carbon-oxygen layer)is mixed up to the layer having an expansion velocity of - 2000 km s^<-1> for a 5% random perturbation. At the same time, hydrogen is mixed down to the core having an expansion velocity of - 500 km s^<-1> for the 5% random perturbation. Heavy elements are preferentially concentrated into the high-density fingers and mushroom heads with a density contrast of - 5-6. These results are essentially the same as in our previous results obtained by a more diffusive hydrodynamic code. However, we have failed to mix ^<56>Ni into the envelope having an expansion velocity of 3000-4000 km s^<-1>. The R-T instability alone may not convey ^<56>Ni into the very surface layer.