Mystery of cosmic rays' origin solved at last

摘要

The protons that smack into Earth's atmosphere at near the speed of light get their energies from exploding stars. At least that's the theory, but direct evidence has been hard to come by-until now. Discovered in 1912, cosmic rays are high-energy charged particles arriving at Earth from space. Nearly all are protons, and some reach speeds higher than any achieved in particle accelerators. But their origins are a puzzle.