This image is from a large scale simulation of a type Ia supernova. A type Ia supernova is believed to be a small star called a white dwarf (a star about the size of the earth with the mass of about 1.4 times that of the sun) that detonates and releases a huge amount of energy. In the image,the blue contour is of density at 1x10^6 g/cm^3 which approximately represents the location of the surface of a white dwarf star and the orange contour is a variable that tracks an interface behind which is the ash left over from nuclear burning.
In this simulation, we start with a tiny spark slightly off center inside of the star. This spark will cause a nuclear flame to spread, burning nuclear fuel and forming a large, hot, buoyant bubble. This bubble quickly grows and rises. After a short period of time (about a second) the bubble bursts out of the surface of the star ejecting the burnt nuclear fuel (ash) flying into space.
The gravity at the surface to the star is very strong however so the ash, which is now moving very fast, gets confined to the surface of the star. This ash spews from the surface of the star like a fountain and since it's confined to the surface of star it very quickly spreads to cover the surface and will eventually collide with itself at the opposite point of where it broke out. We believe this violent collision will cause a detonation that will blow up the entire star. The image shows the simulation after the hot bubble has broken through the surface and the ash is spreading around the surface of the star.
George C. Jordan
ASC FLASH CENTER
University of Chicago