![An artist's illustration of the two supermassive black holes.](https://cdn.mos.cms.futurecdn.net/ULuEivH6M6LDvqcUYSNUAk-320-80.jpg)
Astronomers find heaviest black hole pair in the universe, and they've been trapped in an endless duel for 3 billion years
Two supermassive black holes spotted circling inside a remote 'fossil' galaxy are the heaviest, and the closest, black hole binary ever found.