Non-spherical core-collapse supernovae: evolution towards homologous expansion^*

We study the hydrodynamic evolution of a non-spherical core-collapse supernova in multidimensions. We begin our study from the moment of shock revival and continue for the first week after the explosion when the expansion of the supernova ejecta becomes homologous. We observe the growth and interaction of Richtmyer–Meshkov, Rayleigh–Taylor and Kelvin–Helmholtz instabilities resulting in an extensive mixing of the heavy elements throughout the ejecta.

We obtain a series of models at progressively higher resolution and provide a preliminary discussion of numerical convergence. Unlike in previous studies, our computations are performed in a single domain. Periodic mesh mapping (Couch et al 2009 Astrophys. J. 696 953–70 and Kifonidis et al 2006 Astron. Astrophys. 453 661–78) is avoided. This is made possible by employing an adaptive mesh refinement strategy in which the computational workload (defined as the product of the total number of computational cells and the length of the time step) is monitored and, if necessary, limited.

Our results are in overall good agreement with the simulations reported by Kifonidis et al (2006 Astron. Astrophys. 453 661–78). We demonstrate, however, that the amount of mixing and the kinematic properties of radioactive species (i.e. ⁵⁶Ni) are extremely anisotropic. In particular, we find that the model displays a strong tendency to expand laterally away from the equatorial plane towards the poles. Although this tendency is usually attributed to numerical artefacts characteristic of computations with assumed symmetry (axis effect), the observed behaviour can be largely explained by the structure of the neutrino-driven explosion model. Future studies are needed to establish to what degree the morphology of a young supernova remnant can be used to probe early stages of the explosion especially in situations when the standing accretion shock instability is at work within the first second after core bounce.