Mystery of cosmic-ray origins deepens

BBC : The origin of the highest-energy cosmic rays—charged subatomic particles that streak to Earth from outer space—may be one of the longest-standing questions in astrophysics. Only two sources were thought possible, supermassive black holes or gamma-ray bursts (GRBs). Now researchers at the IceCube neutrino telescope, who published their findings yesterday in Nature, say that GRBs are not the sole source of the high-energy cosmic rays. Computer models had predicted that GRBs would generate a stream of neutrinos, among other particles. However, over a period of two years when some 300 GRBs were recorded by NASA’s Swift spacecraft and other observatories, IceCube scientists did not detect the levels of neutrinos that GRBs should produce. IceCube is searching for neutrinos from active galactic nuclei, but the results so far have been inconclusive.