Numerical simulation of mixing in supernova ejecta

对SN 1987 A的观测强烈地暗示了在爆炸过程中发生了大规模的混合。最有前途的机制，混合喷出物是瑞利-泰勒（R-T）不稳定性，使我们有数值遵循的R-T不稳定性的非线性增长，使用更精细的二维（2-D）轴对称流体动力学代码比我们以前的工作。R-T不稳定性的增长强烈地依赖于初始扰动的幅度。结果表明，即使对速度场作1%的扰动，不稳定性也会显著增加。HE/C+O界面不稳定，H/He界面不稳定。最终，核心材料（在碳-氧层内部）混合到具有5%随机扰动的~ 2000 km/s的膨胀速度的层<-1>。同时，氢向下混合到核心，对于5%的随机扰动，其膨胀速度为~ 500 km/<-1>s。重元素优先富集在高密度指状体和蘑菇头中，密度对比度为-5-6。这些结果基本上是相同的，在我们以前的结果得到了一个更扩散的流体动力学代码。然而，我们未能将^ Ni混入<56>膨胀速度为3000-4000 km/s^的包层中<-1>。R-T不稳定性本身可能不会将^ Ni输送<56>到最表层。

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.