In a first, an image shows a dying star exploded twice to become a supernova 

For the first time, astronomers have spotted a star that exploded not once, but twice. A new image of a roughly 300-year-old supernova provides visual evidence that some dying stars undergo a double explosion, researchers report July 2 in Nature Astronomy.

Supernovas usually mark the death of massive stars. But medium-sized ones, like the sun, can also go out with a bang. When midsize stars exhaust their hydrogen fuel, they shed everything but their core, leaving behind small inert objects called white dwarfs. These incredibly dense remnants are about the size of Earth with roughly the mass of the sun.