Neutrinos shed light on cosmic rays

Thanks to the coordinated work of about 20 laboratories, physicists suspect a blazar, a black hole at a center of a very active galaxy, to be the source of extra-galactic neutrinos. The purpose of the IceCube laboratory, set on the Amundsen-Scott base near the South pole is to detect neutrinos indirectly. In fact the result of the interaction of a neutrino with an atom of ice can be detected. On 22 september 2017, IceCube detected a muon which is the signature of a muon neutrino, the energy and the direction of the initial neutrino were inferred from the data collected by some of the 5160 detectors composing the IceCube installation (covering a volume of 1 km³ of ice). Neutrino's energy was about 290 TeV and such energy hints at an extra-galactic origin. At the moment of the detection an automatic message was sent to other observatories to point their instrument to the direction of the neutrino. The Fermi satellite was the first to detect a very active gamma source, a blazar 4 billion light-years away from earth. It is very likely that this blazar is also the source of this very high energy neutrino. (A.C.)