In 2010, observers reported the most massive stars ever seen, exceeding what many astronomers thought was a ceiling around 150 times the mass of our sun. The most flagrant violator had about twice the legal limit. The heavyweight champs resided 160,000 light-years from Earth in Radcliffe 136 (far right image above), a dense star cluster within the Large Magellanic Cloud, the brightest galaxy that revolves around our own. Now, as astronomers will report in Monthly Notices of the Royal Astronomical Society, they have simulated the evolution of this star cluster, finding that a stellar heavyweight can arise when two massive stars born orbiting each other merge into a single behemoth due to the frequent juggling of other stars in such a dense environment. The idea is plausible, because massive stars usually have partners, but observers need to test the claim by measuring how fast the record-breaking stars spin. If they're really the product of stellar mergers, they should spin fast: As two stars merge, the angular momentum of their orbital motion spins up the single merged star so that it whirls rapidly.
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