Modeling Sub-Chandrasekhar Type Ia Supernovae

The explosion of sub-Chandrasekhar-mass white dwarfs via the double detonation scenario is a potential explanation for Type Ia supernovae. In this scenario, a surface detonation in a helium layer initiates a detonation in the underlying carbon/oxygen core leading to an explosion of the whole star. To judge how well this theoretical model reproduces observations in comparison to other scenarios, detailed numerical simulations and the calculation of synthetic spectra and light curves are necessary. However, solving the reactive Euler equations for explosive nuclear burning in full star simulations is challenging because of the very wide range of scales that are involved: from the white dwarf radius of several thousand kilometers down to the carbon burning length scale that can be as small as 0.1 mm. Therefore, we use approximate schemes for nuclear burning in our hydrodynamic simulations that treat the detonations as reactive discontinuities, propagate them at the correct speed and release an approximately correct amount of energy behind the front. More accurate nucleosynthesis is determined afterwards in a post-processing step from the density and temperature trajectories of Lagrangian tracer particles that we passively advect with the flow in the hydrodynamic simulations. Here, we present details of our burning scheme and discuss simulation results.