Contact: Andy Freeberg
DOE/SLAC National Accelerator Laboratory
Caption: In order to understand the origin and acceleration of cosmic ray protons, researchers used data from the Fermi Gamma-ray Space Telescope and targeted W44 and IC 443, two supernova remnants thousands of light years away. Both turned out to be strong sources of gamma rays, but not at energies below what neutral pion decay would produce -- the observational proof scientists had been looking for.
Credit: NASA/DOE/Fermi LAT Collaboration
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Related news release: Proof: Cosmic rays come from exploding stars