TYPE Ia SUPERNOVAE: THE FLAME IS BORN

摘要

The nuclear runaway that culminates in the explosion of a nearly Chandrasekhar mass white dwarf as a Type Ia supernova begins as stable convective carbon burning. As the central temperature rises to approximately 7 x 10~8 K, mixing length theory fails as the convective cycle time becomes comparable to the nuclear burning time. Using a simple analytic model and a realistic presupernova star, we explore the evolution of burning blobs as they "float" in response to the buoyancy produced by nuclear burning. The more rapidly moving of these blobs accelerate to approximately 100 km s~(-1) and travel several hundred kilometers before nuclear reactions accelerate so rapidly that burning is completed in place. After burning to a temperature near 10~(10) K, the blobs become even more buoyant (Δp/p ～ 25%) and accelerate to a fraction of the sound speed. A negative heat capacity due to α-particle recombination assists here. Our calculations suggest different starting conditions than usually employed by those doing multidimensional calculations of these events. Moreover, velocities of burning regions of a fraction of the sound speed may not be too difficult to achieve.