More than one way to explode a star

There are two ways to light a cosmic candle. One technique calls for two white dwarf stars; another positions a white dwarf near a larger stellar companion. Both combinations produce type 1a supernovas (pictured here), massive stellar explosions that act as “standard candles” for gauging astronomical distances. Type 1a supernovas are triggered when white dwarfs gain weight, igniting a runaway thermonuclear reaction that destroys the dwarf, producing a fireball of predictable brightness. For a long time, astronomers disagreed over what sorts of ingredients were needed to make the white dwarf go boom.  Now, an international team of astronomers studying 23 recent type 1a fireballs reports that there are two recipes: the same ones astronomers have been arguing over for years. In both, the doomed dwarf leeches material from a companion — from either a second dwarf, producing a supernova with no surrounding gas, or from a larger star, generating a more powerful explosion and a gas cloud, the team reports in an upcoming issue of the Astrophysical Journal. In January, another team published evidence that a white dwarf–white dwarf merger produced a type 1a supernova. Understanding precisely how these type 1a explosions are generated will help refine cosmic distance measurements, helpful information for gauging the accelerating expansion of the universe.