In a type "Ia" supernova, a white dwarf star explodes after it gains matter from a companion star in the same binary star system. One of the leading theories is that the supernova happens when two white dwarf stars merge. But a competing theory says that the companion could be a normal or giant star that survives the explosion, although not without some damage.
Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star and how it triggers the explosion have remained elusive for decades. The supernova, named iPTF14atg, is located 300 million light years away in the galaxy IC831.