NONLINEAR GROWTH OF RAYLEIGH-TAYLOR INSTABILITIES AND MIXING IN SN-1987A

Optical, X-ray, and gamma-ray light curves of SN 1987A and broad emission lines of heavy elements strongly suggest the occurrence of large-scale mixing during the explosion. Using a two-dimensional hydrodynamic code, we have numerically demonstrated a nonlinear growth of the Rayleigh-Taylor (R-T) instability in the ejecta of SN 1987A, which confirmed the linear stability analysis of Ebisuzaki, Shigeyama, and Nomoto and the two-dimensional hydrodynamical simulation of Arnett, Fryxell, and Müller 1989. After the blast shock breaks out of the helium core (∼100 s after the explosion), a strong reverse shock forms behind the hydrogen/ helium (H/He) interface and the R-T instability begins to largely grow at the H/He interface. Mushroom-like structures appear ∼2000 s after the explosion. Eventually the core material (inside the carbon-oxygen layer) is mixed up to the layer having an expansion velocity of ∼2200 km s-1 if the initial perturbation is as large as 5%. At the same time, hydrogen is mixed down to the core having an expansion velocity of ∼800 km s-1. The core material is concentrated into the high-density fingers with a density contrast of a factor of 5-6. Thus, the mixing due to the R-T instabilities can reproduce most of the observational indication of mixing in SN 1987A.