You might not spend much time pondering the source of cosmic rays. But they bombard our atmosphere constantly, and astronomers have long been curious about their source. Finally, this year they pinned it down: These most energetic particles known stream from hyperactive black holes. Knowing where they come from is a bit like knowing light comes from the sun — it allows you to study an object by observing its emanations. The discovery ushers in "the age of cosmic-ray astronomy," one researcher said.
