Preparing for an Explosion: Hydrodynamic Instabilities and Turbulence in Presupernovae

Both observations and direct numerical simulations are discordant with predictions of conventional stellar evolution codes for the latest stages of a massive star's life prior to core collapse. We suggest that the problem lies in the treatment of turbulent convection in these codes, which ignores finite amplitude fluctuations in velocity and temperature, and their nonlinear interaction with nuclear burning. The hydrodynamic instabilities that may arise prompt us to discuss a number of far-reaching implications for the fates of massive stars. In particular, we explore connections to enhanced presupernova mass loss, unsteady nuclear burning and consequent eruptions, swelling of the stellar radius that may trigger violent interactions with a companion star, and potential modifications to the core structure that could dramatically impact calculations of the core-collapse mechanism itself. These modifications may be of fundamental importance to the interpretation of measured isotopic anomalies in meteorites, changing the predictions of both mixing and detailed nucleosynthesis, and of young core-collapse supernova remnants. They may also make possible the development of an early warning system for the detection of impending core collapse.