Video: Stellar cataclysm
The protons that constantly smack into Earth’s atmosphere at near the speed of light get their huge energies from exploding stars. At least that’s what physicists and astronomers had long suspected, but direct evidence for the idea has been difficult to come by – until now.
Cosmic rays are any charged particles arriving at Earth from space. Nearly all of them are protons, and some have been accelerated to speeds higher than any achieved by a particle accelerator on Earth. Although we have known about cosmic rays since 1912, their origins have remained a puzzle.