Microscopic and Macroscopic Modeling of Thermonuclear Burning Fronts

Abstract

Observational constraints as, for instance, the amount of intermediate mass elements needed to fit SN Ia spectra, in combination with numerical nucleosynthesis calculations imply that if these events are to be explained by thermonuclear explosions of Chandrasekhar mass C+0-white dwarfs, the explosions begin in the subsonic deflagration mode as opposed to supersonic detonations (Woosley 1990). In deflagrations, thin sheets of burning material (“flames”) propagate by means of electronic thermal conduction (Timmes & Woosley 1992). On scales larger than a few centimeters the flame is subject to various instabilities that deform its surface, making the macroscopic properties of the wrinkled burning front (the so-called “turbulent flame brush”) more complex than, or even independent of, its laminar propagation characteristics (Woosley 1990, Livne 1993, Khokhlov 1993, 1994, 1995, Niemeyer & Hillebrandt 1995a, b). According to our current knowledge, the turbulent deflagration phase can in principle terminate in three different ways: First, the released energy may be sufficient to unbind the star and produce an explosion which could be compared with SN Ia events. Alternatively, it was suggested that the flame brush makes a transition to a “delayed detonation” after the density has decreased to some 10⁷ g cm^-3 (Khokhlov 1991a, b, Woosley 1994). And, finally, if too little carbon is burned to unbind the star before the flame reaches densities below 10⁷ g cm^-3m.