Lowering detectors into the ice cap

The Antarctic Muon and Neutrino Detector Array (AMANDA) is the world's largest detector of the mysterious neutrino--and the first that can claim to be an astronomical instrument rather than a physics experiment. It trades sensitivity for the sheer size needed to catch a meaningful number of high-energy neutrinos from distant objects, which include many of the violent felons on astronomers' most wanted list: the swirling gas around black holes, the innards of stellar explosions, the decomposition of the unidentified matter that dominates our cosmos.

Inside the hole

So far the observatory, a $7-million collaboration among U.S., Belgian, Swedish and German universities, consists of 424 glass orbs, each the size of a basketball. They watch for the eerie blue glow indirectly emitted when neutrinos collide with atomic nuclei in the ice or underlying rock. The orbs point downward so that Earth will screen out extraneous particles. To deploy them, workers first used pressurized hot water to melt a column of ice half a meter across and 2,400 meters deep. Then they lowered in the orbs, strung on a cable like beads on a necklace, and let them freeze in place. Ultimately, scientists want 5,000 orbs on 80 cables throughout a cubic kilometer of ice.

It turns out that ice is a friendly place for neutrino detectors. At depth it is crystal-clear, so the orbs can spot flashes of light hundreds of meters away. AMANDA exemplifies a new breed of telescope that has redefined what it means to "see."