Three-dimensional Structure of Incomplete Carbon–Oxygen Detonations in Type Ia Supernovae

Abstract Carbon–oxygen (CO) detonation with reactions terminating either after burning of 12 C in the leading 12 C + 12 C reaction or after burning of 12 C and 16 O to Si-group elements may occur in the low-density outer layers of exploding white dwarfs and be responsible for the production of intermediate-mass elements observed in the outer layers of Type Ia supernovae. Basic one-dimensional properties of CO-detonations have been summarized in our previous work. This paper presents the results of two- and three-dimensional numerical simulations of low-density CO-detonations and discusses their multidimensional stability, cellular structure, and propagation through a constant low-density background. We find three-dimensional CO detonations to be strikingly different from their one-dimensional and two-dimensional counterparts. Three-dimensional detonations are significantly more robust and capable of propagating without decay compared to highly unstable and marginal one- and two-dimensional detonations. The detonation cell size and whether burning of 12 C in a three-dimensional detonation wave is followed by the subsequent 16 O burning are sensitive to both the background density and the initial 12 C to 16 O mass ratio. We also discuss the possible implications for understanding the observed early-time bumps in light curves.