ON AUGUST 24th 2001 the Parkes Observatory, in Australia, picked up an unusual signal. It was a burst of radio waves coming more or less from the direction of the Small Magellanic Cloud, a miniature galaxy that orbits the Milky Way. This burst was as brief as it was potent. It lasted less than 5 milliseconds but, during that period, shone with the power of 100m suns. It was, though, noticed by astronomers only in 2007, when they were poking around in Parkes's archived data. As far as they can tell, it has never been repeated.
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