# Where do high-energy neutrinos come from?

Last week the IceCube South Pole Neutrino Observatory published a press release reporting the possible discovery of two neutrinos with energies of over 1 PeV.

Would anyone here be willing to help me understand the significance of this announcement? Although it was reported in the press that these neutrinos originated from outside our galaxy, the original press release seemed to say that this might possibly be the first sighting of 'astrophysical' neutrinos. Are there other observations of extragalactic neutrinos? Are there any conjectures as to processes which might generate? How would a neutrino even be accelerated if it is unaffected by magnetic fields?

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"How would a neutrino even be accelerated if it is unaffected by magnetic fields?" 1 PeV is way beyond the electroweak unification scale. From the Dermer paper arxiv.org/abs/astro-ph/0611191v1 , it looks like the main process is high-energy scattering of gamma rays with protons. High-energy pions are produced, which then decay into stuff including neutrinos. – Ben Crowell Apr 30 '13 at 19:52

Possible extragalactical sources for high energy neutrinos is still an open question. There are several candidates, look at this paper on arXiv. By the way, astrophysical neutrinos have been already detected more than 20 year ago by Kamiokande in Japan. They came from supernova SN 1987A, and helped to set an upper bound (of about $10\ \text{eV}$) on the sum of the masses of the three neutrino species. This neutrino source was in fact extragalactical (from the Large Magellanic Cloud).