IceCube is a neutrino telescope, consisting of a layer of ice interlaced with photomultipliers more than 1,000 meters below the surface in the Antarctic. Neutrinos are very low mass, ghostly particles which seldom interact with matter. IceCube detects neutrinos by recording Cherenkov photons emitted from secondary leptons produced in very rare interactions of neutrinos with water molecules in the Antarctic’s glacial ice. IceCube began observations in December 2010. Most neutrinos IceCube is expected to see originate in the Sun or cosmic rays interacting with the Earth’s atmosphere.
The first two years of data have been reduced, and two very high energy neutrino events were found (although at a level of statistical significant is just below the point where they would be considered robust detections). These two events were whimsically named Bert and Ernie. The amazing part for me was the incredible energy of these neutrinos; 1.04 +/- 0.16 PeV and 1.14 +/- 0.17 PeV. That’s Peta eV, a thousand million million electron volts, or the mass equivalent of a million protons.
This energy level means that, as understood today, the neutrinos were unlikely to have originated near the Earth (or as an effect of the GZK cutoff for intergalactic cosmic rays). This is a tantalizing hint that we may have new astronomical neutrino sources out there! But with so few detections–I can’t really call them observations yet–it is hard to say anything with any degree of certainty. I’ve heard of some new results at lower energy which are reported to be statistically significant, but I don’t have any real info. Yet.
Neutrino astronomy is in its infancy, but already we are seeing hopeful signs of new physical phenomena just waiting to be explored.