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.
Cosmic rays have proved an enduring mystery because their interactions obscure their origins. Being charged particles, they “feel” the push and pull of magnetic fields in space. As a result, they travel across the galaxy in long, looping paths that make it impossible for detectors on Earth to trace where they’ve come from.
The speed at which the particles travel suggests that they must come from some violent, high-energy source. Researchers have long suspected supernova remnants but had no way of proving it.