
One stellar explosion can't get enough of the spotlight. After showing up five times in images taken by the Hubble Space Telescope, the bizarre "reappearing supernova" is now helping scientists solve one of astronomy's biggest mysteries: how fast the universe is expanding.
About 13.8 billion years ago, the universe as we know it was just a tiny point in space, containing all the matter in existence. Then, an explosion occurred: the Big Bang. That matter rushed outward — and continues to do so today, gaining speed all the time.