When people hear “supernova” they usually think of a star that runs out of fuel. Without the engine of nuclear fusion to heat it, the star collapses under its own weight, which triggers a huge explosion. This is a “core-collapse supernova,” one of the most energetic events in the universe. The result is usually a neutron star or a black hole. However, there’s another type of supernova, one in which a star whose nuclear fires long ago petered out is reignited, causing a catastrophic explosion. This is the type Ia supernova. We start our story with the type of