The star cluster R136 is already home to the largest known star in the universe, a giant more than 250 times the mass of the sun. Now, astronomers observing the cluster in ultraviolet light using the Hubble Space Telescope have found a total of nine stars with masses of more than 100 suns, the largest collection of very massive stars found to date. This pack of heavyweights—located in the Tarantula Nebula (shown above with R136 right of center) some 170,000 light-years from Earth—burns bright and fast, collectively outshining the sun 30 million times and ejecting every month material equivalent to the mass of Earth. But how they form is a mystery—the current theory of star formation cannot explain how such behemoths could come together from the collapse of a cloud of gas and dust. It has been suggested that they grow through the merger of pairs of binary stars but, as the team explains today in the Monthly Notices of the Royal Astronomical Society, current understanding of binary mergers cannot explain this number of giants in close proximity. The team plans to continue observing R136 with Hubble in visible light, searching for binaries that could merge to produce such massive stars.