Neutrinos put cosmic ray theory on ice

21 June 2012

The IceCube telescope buried beneath the South Pole has failed to detect any high energy neutrinos accompanying exploding fireballs in space, undermining a leading theory of how cosmic rays are born (Nature 484:351,2012).

IceCube, a detector made up of 5,160 optical sensors embedded up to 2.5km deep in the Antarctic ice, searched for evidence of neutrinos emitted from 300 fireballs, known as gamma ray bursts (GRBs), observed between May 2008 and April 2010. In Nature the team behind the experiments report that the search did not find a single neutrino, a result that challenges the idea that cosmic rays originate from GRBs. The finding is likely to focus attention on the other prime candidate for creating cosmic rays: the massive black holes found at the centre of active galaxies.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man made particle accelerators. Understanding their origins would provide crucial insights into the most energetic phenomena in the Universe.

Professor Subir Sarkar, who is a member of IceCube, said: "Although this is a negative result it illustrates that cosmic neutrino detection has come of age – IceCube has achieved the necessary sensitivity to neutrino fluxes expected from likely sources of cosmic rays. It should not be long now before we find the real sources."

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