Where Do High-Energy Cosmic Rays Come From? A Star’s Last Gasp
For over a century, physicists have been flabbergasted by the existence of cosmic rays, which are charged particles—mostly protons—from outer space that bombard the Earth, thousands per square meter every second. Cosmic rays can reach our planet with speeds driven by over a peta-electron volt, or PeV, of energy. (That’s a quadrillion electron volts—a hundred times higher than what can be achieved with the LHC.) And though there’s no shortage of cosmic rays to study, scientists have mostly been in the dark about exactly what can push particles to such extreme speeds.
Earlier this month, a new paper in Physical Review Letters shed some light on this mystery. By combining data from NASA’s Fermi Gamma-ray Space Telescope with observations from nine other experiments, a team of five scientists has conclusively identified a supernova remnant as a source of PeV protons. Discovering these cosmic ray “factories”—called PeVatrons by the scientists who study them—will eventually help them characterize the environmental conditions that propel these particles and the role they play in the evolution of the cosmos.
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