Buried deep in the pristine Antarctic ice lie 5,160 basketball-sized detectors that look for flashes of blue light.
This radiation signals that a high-energy particle has interacted with an atom of the ice and given off some energy in the process. Scientists built the underground cubic kilometer IceCube detector to find a specific type of particle called a neutrino. This particle has no electric charge, is nearly massless, and interacts extremely weakly with matter. (In fact, billions of them are zooming through you as you read this story.)
Astronomers have detected neutrinos from the Sun and from Supernova 1987A when a massive star exploded. Now, the IceCube team reports in the November 22 issue of Science that it has found 28 high-energy neutrinos during a two-year all-sky search. The newly discovered particles have energies at least a million times that of the SN 1987A neutrinos.
At most, 11 of the 28 detected signals could result from background events or atmospheric neutrinos — those created as high-energy particles called cosmic rays collide with atoms and molecules in Earth’s atmosphere and create secondary particles. However, the researchers say the neutrinos don’t have the characteristics of atmospheric ones.
They looked in the data for evidence of multiple neutrinos originating from a specific location on the sky or arriving at a similar time but were unable to trace the 28 neutrinos to specific sources. Most of the detected signals correspond to locations on the Southern Hemisphere sky.
Scientists can calculate the energies of the incoming neutrinos from the light the detectors register. The 28 particles discussed in the Science study had energies ranging from 30 trillion electron volts (TeV) to 1,141 TeV; visible light has energy between 1.5 and 3 electron volts. The data also include the two highestenergy neutrinos ever observed. — L. K.
Source: Astronomy March 2014
