Pictures of a distant supernova remnant show two concentric rings, providing clear evidence that exploding white dwarf stars go boom twice in the blink of an eye

An explosion captured in a new image could help astronomers to better understand the "standard candles" at the center of a major cosmological mystery.

There's widespread agreement that type Ia supernovae are the explosions of white dwarf stars. Normally, these stars are composed primarily of moderately heavy elements like carbon and oxygen, and lack the mass to trigger additional fusion.