We've spotted the shock wave from an invisible explosion in space

It started with a bang – at least, it must have. Astronomers have spotted a weird radio signal from space that appears to be the shock wave from an enormous explosion, but we never saw the explosion itself.

Casey Law at the University of California Berkeley and his colleagues were comparing two maps of radio wave sources in the sky when they noticed something strange: an object that had been one of the brightest on a map generated in 1993 had faded by a…