Last year British astronomers identified the most massive star ever seen: a behemoth weighing 265 times as much as our sun, so huge that it challenges astronomers’ models of how stars are born. Those models suggested that stars max out at 150 solar masses; anything more was thought to be too unstable to coalesce. But Paul Crowther of the University of Sheffield, examining images from the Very Large Telescope in Chile and the Hubble Space Telescope, identified four young stars (pdf) exceeding that mass in R136, a stellar cluster 165,000 light-years away. The new heavyweight, dubbed R136a1, shines as bright as 10 million suns.

Normal stars form when clumps of gas and dust collapse due to gravity, but Crowther says this is inadequate to explain R136a1. Possibly it beefed up by colliding and merging with other young stars in the cluster. As for the fate of these huge stars, he adds, “They could explode as spectacular supernovas and leave no remnants behind.”