Initiation of the detonation in the gravitationally confined detonation model of Type Ia supernovae

We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). In this model, ignition occurs at one or several off-center points, resulting in a burning bubble of hot ash that rises rapidly, breaks through the surface of the star, and collides at a point on the stellar surface opposite the breakout, producing a high-velocity inwardly directed flow. Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from the flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from 1D simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave pre-conditions the temperature in the fuel in such a way that the Zel’dovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of Department of Physics, The University of Chicago, Chicago, IL 60637 Joint Institute for Nuclear Astrophysics, The University of Chicago, Chicago, IL 60637 Max-Planck-Institute for Astrophysics, 85741 Garching, Germany The Center for Astrophysical Thermonuclear Flashes, The University of Chicago, Chicago, IL 60637 Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 Steward Observatory, The University of Arizona, Tucson, AZ 85719 Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637 Argonne National Laboratory, Argonne, IL 60439