Bullets of the Cosmos The origin of cosmic rays is a 90-year-old mystery. Most of these high energy nuclei are thought to be hurled at us by supernova shock fronts, perhaps from collisions with dust grains. Future measurements of the abundances of trace elements in cosmic rays can determine the nature of their sources and the time between the elements creation and acceleration. The distribution of cosmic-ray energies is remarkable in that it is almost a constant power law over at least 13 decades in energy. A small steepening, or “knee,” in the power law near 10^15 eV is thought to represent the limit to energies achievable by supernova shock acceleration. A mission designed to measure the composition of these cosmic rays will explore their connection to supernovae by identifying these high energy nuclei. At higher energies, the mystery deepens. In fact, we have detected cosmic rays up to about 10^20 eV, where individual atomic particles have the energy of a well-hit baseball! About the only conceivable sources for these particles are galactic nuclei, giant extraga lactic double radio sources, or the mysterious sources that give rise to gamma-ray bursts.
Posted on: Sun, 26 Jan 2014 09:48:30 +0000
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