Icy observatory launches neutrino hunt.

Locked in crystal-clear ice more than a kilometer below the South Pole's surface, an array of glass bulbs the size of bowling balls watches for telltale flashes of blue light.

The photomultiplier tubes--422 of them so far--are the eyes of the Antarctic Muon and Neutrino Detector Array (AMANDA), an instrument whose mission is to detect elusive subatomic particles known as neutrinos arriving from space (SN: 10/5/91, p. 219).

"The news is that, after 30 to 40 years of people dreaming about a large neutrino telescope, it finally exists, and it works, and it can be expanded to a kilometer cube," says Francis Halzen of the University of Wisconsin-Madison. He came up with the idea of the ice-bound telescope a dozen years ago.

When neutrinos strike the nuclei of atoms in ice, they can spawn muons and other particles, which emit light as they speed through the frozen mass. Since the 1960s, neutrino detectors consisting of underground tanks of liquid surrounded by photomultiplier tubes have observed tracks of neutrinos from the atmosphere and sun. These tanks can't detect the rare, high-energy neutrinos that the ice may capture.

AMANDA's cylindrical array of tubes already exceeds 120 meters in diameter and 400 meters in depth, dwarfing other neutrino detectors, and tubes are still being added. Because of its large volume, scientists expect AMANDA to detect significant numbers of the high-energy neutrinos that theorists suspect are generated by cosmic sources, such as black holes.

On March 3, the University of Wisconsin reported that--after 7 years in construction, including a year of tuning and testing--the $7 million telescope has begun its hunting.