Image: ROBERT MORSE
The Antarctic Muon and Neutrino Detector Array (AMANDA) at the South Pole is no ordinary telescope. For one thing, its 677 detectorsarrayed in a cylinder 120 meters in diameterare buried more than one-and-a-half kilometers beneath the snow (right). And instead of looking up, they point down, straight through the center of the Earth. But according to results published in today's issue of Nature, AMANDA's odd configuration works like a charm: the telescope has now made its first sighting of elusive astronomical objects known as high-energy neutrinos.
"We have proven the technique," says Francis Halzen, a professor at the University of Wisconsin-Madison and lead author of the new paper. "We have a unique probe with a sensitivity well beyond other experiments, and the neutrinos we've seen are of a higher energy than has been seen before." The neutrinos AMANDA spotted this time around came from cosmic rays crashing into Earth's surfacewhich are not scientifically the most interesting. The fact that the instrument detected them, however, gives scientists hope of tracing other neutrinos to more exotic, distant and violent events in the universe, including exploding stars and active galactic nuclei.
AMANDAs secret is that it points down, using Earth to filter out everything but high-energy neutrinos. Unlike other forms of radiation, beams of invisible, uncharged and nearly massless neutrinos can pass through stars, planets, magnetic fields and other obstacles undeterred. They are also the only high-energy particles that can convey information from the outer edges of the universe, says Principal Investigator Robert Morse at UW-Madison. "This is our coming-out party," he says of the latest results. "Now we start the process of discovery."