A bizarre telescope of sorts buried deep beneath the antarctic ice has mapped the first flight paths of energetic neutrino particles bombarding Earth from space. The Antarctic Muon and Neutrino Detector Array (AMANDA) consists of several kilometer-long strands of glass detectors the size of bowling balls. So far it hasn't identified a source for cosmic neutrinos, but astronomers believe the project and its successors will soon capture particles from some of the most exotic powerhouses in the universe.
Extragalactic neutrinos come from elementary particles that collided shortly after the big bang or crashed into each other while orbiting massive objects like black holes. Neutrinos interact with other material so rarely that they pass like ghosts through almost any machine built to catch them. Vast underground water tanks occasionally catch sight of a relatively low-energy neutrino streaming out from the sun, but these "telescopes" can't gather enough neutrinos from distant objects to do much research on them, and such detectors often can't tell what direction the neutrino came from.
But AMANDA can. Instead of looking up at the sky like a normal telescope, the AMANDA detector looks down. Its 500-meter by 120-meter array of 677 detectors in glass globes dangle like love beads from electrical cables 1.5 kilometers down into South Pole ice. The earth filters out every form of radiation except the neutrinos. A few collide with ice molecules, creating a shower of light called Cerenkov radiation. The detector globes sparkle like synchronized Christmas lights as the narrow Cerenkov beam successively illuminates each globe along its path. By reversing the pattern, astronomers can trace the neutrino back to its origins. AMANDA has registered 188 neutrino-like "events" so far, but researchers can't yet confirm that any came from an extragalactic object rather than a closer source, such as cosmic rays colliding with particles in Earth's atmosphere. "But we are going to turn up the sensitivity and hope we run into a discovery," says astrophysicist Francis Halzen of the University of Wisconsin, Madison.
For now astronomers are just happy that AMANDA works as planned. They expect the big discoveries to come when AMANDA is expanded into ICECUBE, a kilometer-square array of 4800 detectors. "AMANDA is much like the Model T Ford, a great breakthrough, a great initial success," says astrophysicist John Bahcall of the Institute for Advanced Study in Princeton, New Jersey. "But we won't be satisfied until we have ICECUBE, the Cadillac of neutrino telescopes."
The AMANDA site