Supernova interaction. Computer model of matter density variations around a star (red) ten minutes after its companion star exploded as a supernova. The exploding companion star is out of frame at top. Density is colour-coded from red (high) to dark blue (low). Ejected matter from the exploding star forms complex vortices, shock fronts and eddies as it interacts with this star. This system is a type 1a supernova. These occur in binary star systems in which the exploding star is a white dwarf. The small, dense dwarf accretes gas from its neighbour until nuclear reactions begin, ulti- mately causing the dwarf's explosive destruction.