Cosmic convergence

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Science  31 Jul 2015:
Vol. 349, Issue 6247, pp. 465-467
DOI: 10.1126/science.349.6247.465

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A year and half ago, physicists working with the massive IceCube particle detector—a 3D array of 5160 light sensors buried kilometers deep in ice at the South Pole—spotted ghostly subatomic particles called neutrinos from beyond our galaxy. The discovery is Nobel-caliber stuff, some physicists say, as, except for a burp from a nearby supernova explosion in 1987, neutrinos from the far reaches of the cosmos had eluded capture. However, IceCube saw only about a dozen cosmic neutrinos per year, a rate at which the $279 million detector might never see enough of them to work as advertised: as a neutrino telescope with which to view the heavens in a whole new way. But as the data continue to come in, researchers are optimistic that a big enough detector should be able study the sky through neutrinos. IceCube researchers are pushing to expand the array, and other researchers have developed approaches that they say could be cheaper and more efficient. More important, a convergence of observations suggests that cosmic neutrinos spring from the same astrophysical sources as other particles from space: highly energetic photons called gamma rays, and mysterious ultra-high energy cosmic rays—protons and heavier atomic nuclei that reach energies a million times higher than humans have achieved with particle accelerators. If so, physicists have only one mystery to solve.