It's one surprise after another. The detection of gravitational waves announced earlier this year sent ripples through the world of physics. The signal was thought to come from two gigantic black holes merging into one, but now a group says it could have come from something even more exotic - a gravastar. No one is disputing the first detection of gravitational waves. The Laser Interferometer Gravitational-Wave Observatory (LIGO) team announced in February that it had seen these ripples in space-time predicted by Albert Einstein's theory of relativity (see page 33). "We're not trying to say LIGO was wrong," says Paolo Pani of the Sapienza University of Rome, Italy. But Pani and his colleagues say the signal might not have come from a black hole merger.
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