Earth is under siege from outer space! In a way. We get peppered by speedy particles, called cosmic rays, all the time. Some come from the sun, some from supernovas and some via solar-style winds emanating from far-off massive stars. Anything that can accelerate a proton to nearly light speed does the trick.
But all cosmic rays are not created equal. The most energetic among them are single atomic nuclei that strike Earth's atmosphere with the energy of a well-thrown baseball. The source of these ultraenergetic cosmic rays is unclear. But, thanks to a new study, one of the leading candidates has probably been ruled out.
Gamma-ray bursts occur when a massive star collapses in on itself. It had been thought that these ultra-energetic bursts might produce super high-energy cosmic rays. But a giant Antarctic neutrino detector called IceCube has been looking for neutrinos that should accompany the high-energy cosmic rays from a gamma-ray burst. And it hasn't seen any, researchers announced in the journal Nature. [The IceCube Collaboration,"An absence of neutrinos associated with cosmic-ray acceleration in gamma-ray bursts"]
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There is another possibility: that flaring black holes are what's hurling cosmic baseballs our way. That idea is looking better now that gamma-ray bursts have been called out.
—John Matson
[The above text is a transcript of this podcast.]
[Scientific American is part of Nature Publishing Group.]
