Type Ia supernovae are thought to be the result of a thermonuclear explosion in a white dwarf that is approaching the Chandrasekhar mass limit. The properties of the supernova explosion, including its energy, depends significantly on the way in which the thermonuclear runaway begins. Where in the white dwarf ignition takes place, and how many ignition points there are, are important unsolved questions. We discuss the challenges of modeling Type Ia supernova during the several hours before thermonuclear runaway using the FLASH code. In three-dimensional hydrodynamic codes, the pre-supernova white dwarf can exhibit ``ringing'' at the fundamental frequency of the star that is driven by numerical noise. These solutions manifest themselves as undamped velocity waves (the white dwarf "breathes in and out") that reach peak amplitudes of about 200 km s-1. We show the results of several methods aimed at reducing the amplitude of these undamped waves in FLASH. We also discuss some of our experiments in mapping spherically symmetric models, which suggest large scale convective motions of 50 km s-1 a few hours prior to ignition, onto a three-dimensional mesh. This work was supported in part by the DOE under the ASCI/Alliance program.
AAS/High Energy Astrophysics Division #7
- Pub Date:
- May 2003