Flames in type Ia supernova: deflagration-detonation transition in oxygen-burning flame

The flame in a Type Ia supernova is a conglomerate structure that, depending on density, may involve separate regions of carbon, oxygen, and silicon burning, all propagating in a self-similar, subsonic front. The separation between these three burning regions increases as the density declines until eventually, below about 2×107 g cm−3, only carbon burning remains active, the other two burning phases having “frozen out” on stellar scales. Between 2 and 3×107 g cm−3, however, there remains an energetic oxygen-burning region that trails the carbon burning by an amount that is sensitive to the turbulence intensity. As the carbon flame makes a transition to the distributed regime (Karlovitz number � 10), the characteristic separation between the carbon- and oxygen-burning regions increases dramatically, from a fraction of a meter to many kilometers. The oxygen-rich mixture between the two flames is created at a nearly constant temperature, and turbulence helps to maintain islands of well-mixed isothermal fuel as the temperature increases. The delayed burning of these regions can be supersonic and could initiate a detonation.