It started as an unremarkable flicker in the night sky. But closer observations revealed that astronomers had captured the largest cosmic explosion ever witnessed, an event thought to have been triggered by a giant cloud of gas being gobbled up by a supermassive black hole.
The flare-up, traced to 8bn light years away, is more than 10 times brighter than any known supernova and has so far lasted more than three years, making it the most energetic explosion on record.
