News FocusAstronomy

What's the Source of the Most Energetic Cosmic Rays?

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Science  01 Jun 2012:
Vol. 336, Issue 6085, pp. 1096-1097
DOI: 10.1126/science.336.6085.1096

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Astrophysicists know that 89% of cosmic rays are simple protons, or hydrogen nuclei. Most of the rest are helium nuclei with a smattering of heavier nuclei, electrons, and antimatter. Astrophysicists think most of the lower-energy particles—up to 1010 eV—come from the sun and that those from 1010 eV up to 1015 or even 1018 eV come from elsewhere in our galaxy. Because cosmic rays with even higher energies seem to come equally from all parts of the sky rather than bunching in the plane of our galaxy, they probably originate outside the Milky Way. Data taken from detectors in the past few years have provided some clues to their origin but, as yet, no smoking gun.