sciencehabit (1205606) writes "For the past century, physicists have puzzled over cosmic rays, particles (mostly protons) that hurtle through space at high speed and seem to come from all directions equally. What's the source of these galactic projectiles? And how do they come to be traveling so fast? Today, an international team announced a major step toward answering those questions: conclusive evidence that at least some of the cosmic rays come from supernova remnants—expanding shells of matter from exploded stars—that are acting as natural particle accelerators."
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