THE record for the most massive star ever measured goes to not one star but two. The size of the binary pair is important because it helps astronomers understand the early universe.
In April Gregor Rauw of the University of Li猫ge in Belgium and colleagues suggested that WR 20a in the constellation Carina could be two giant stars orbiting each other. Twins would explain an otherwise puzzling spectrum of light from the system.
Now Alceste Bonanos and colleagues at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, say that Rauw is right and that the stars are the most massive ever measured. They analysed the variation in brightness of WR 20a for 17 nights using the 1.3-metre Warsaw telescope at Las Campanas Observatory in La Serena, Chile, and say the system is made up of two stars, each of 80 solar masses. The previous record for giant stars was about 60 solar masses.
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Finding and weighing giant stars accurately has become a major preoccupation for astronomers. Radiation from short-lived giants up to 300 times the mass of our sun, or from the black holes that formed when they exploded, might explain an epoch in the early universe called reionisation, when gas that had cooled after the big bang was mysteriously reheated again around 200 million years later. Finding these giants today helps astronomers fine tune their understanding of how early stars might have formed.