Type Ia Supernova A white dwarf with a giant companion can gain mass from its companion As it gains mass, gravity increases – it shrinks When it reaches Chandrasekhar mass it collapses, catastrophically Temperature increases drastically Fusion begins again in the core The entire star explodes, all at once Star is super bright – as bright as an entire galaxy We can see them most of the way across the universe All type Ia supernovae have nearly identical precursors They should blow up almost exactly the same way They should have almost uniform luminosity For reasons that aren't well understood, they are not Some are more efficient than others Amount of time they take to get bright seems to predict luminosity