Can deflagration-detonation transitions occur in type Ia supernovae?

The mechanism for a deflagration-detonation transition (DDT) by turbulent p reconditioning, which has previously been used to explain the possible occu rrence of delayed detonations in Type Ia supernova explosions, is argued he re to be conceptually inconsistent. It relies crucially on diffusive heat l osses of the burned material on macroscopic scales. Regardless of the ampli tude of the turbulent velocity fluctuations, the typical gradient scale for the temperature fluctuations is shown to be of the order of the laminar fl ame width or smaller rather than the homogeneity scale required for DDT, wh ich is larger by more than a factor of 1000. Furthermore, thermonuclear fla mes cannot be fully quenched in regions that are much larger than the lamin ar flame width as a consequence of their simple "chemistry." Possible alter native explosion scenarios are briefly discussed.