ARCADE's mission was to search the sky for heat from the first generation of stars. Instead, it found a cosmic puzzle.


"The universe really threw us a curve," Kogut says. "Instead of the faint signal we hoped to find, here was this booming noise six times louder than anyone had predicted." Detailed analysis ruled out an origin from primordial stars or from known radio sources, including gas in the outermost halo of our own galaxy. The source of this cosmic radio background remains a mystery.