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How to turn a continent into a telescope

By Peter N. SpottsStaff writer of The Christian Science Monitor / March 11, 2004



HONOLULU

Ever since Galileo turned "telescopio" into a household word, tiny packets of light have helped inquisitive people unlock the mysteries of the universe. From radio frequencies to visible light to gamma rays, these photons have led to one stunning discovery after another.

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Nearly 400 years later, Peter Gorham is hoping to use far more ephemeral cosmic particles to delve into the most violent processes of the universe - a task in which photons are of little help. And to do it, the University of Hawaii physicist and his colleagues have embarked on a unique project to turn an entire continent - the Antarctic ice sheet - into the world's largest telescope.

Call it astronomy beyond light. Instead of relying on common photons, researchers are turning to elusive neutrinos to unlock secrets about the universe. These particles have virtually no mass and carry no electrical charge, so they rarely interact with other matter.

Such qualities make neutrinos extremely useful in detecting objects beyond the energy limits of today's astronomy. Besides helping researchers understand some of the most violent processes since the Big Bang, neutrinos could shed light on the mysteries of very high-energy cosmic rays and test theories about the formation of the universe.

"We've got this entire regime of astrophysics that we cannot explore by traditional astronomy. How are we going to get there?" asks Dr. Gorham. "Neutrinos are the obvious choice."

But the same qualities that make neutrinos so valuable also make them terribly difficult to detect. That's why astronomers are trying to fashion such huge "telescopes." At least four other high-energy neutrino projects are in various stages of planning, where neutrino detectors are lowered into Antarctic ice or submerged in the Mediterranean Sea.

Indeed, "the field is exploding," notes John Bahcall, an astrophysicist with the Institute for Advanced Study in Princeton, N.J.

Although neutrino astronomy has been practiced for decades, the main target of observation was the sun. But in 1987 astronomers detected neutrinos in a massive stellar explosion in the Large Magellanic Cloud. That single event not only breathed new energy into supernova research, it also raised hopes that, with the right detectors, other neutrino sources outside the Milky Way could be detected and studied.

The choice to focus on neutrinos is dictated by the peculiarities of high-energy physics. On a human scale, the energy regime Gorham and his colleagues want to probe represents a small percentage of a Curt Schilling fastball. It smacks a mitt and generates a little heat. The dynamics change when that level of energy is imparted to a subatomic particle.

If such a turbocharged particle collides with the nucleus of a particle, "you'll blow the nucleus to smithereens," Gorham says. For photon-based astronomers, this presents a problem.

When a turbocharged photon hits another photon, both vanish and form electrons and positrons. Such collisions - and disappearances - are inevitable because the universe is awash in very low-energy photons. These particles make up the afterglow of the Big Bang, known as the cosmic microwave background. In practical terms, that means astronomers can't use very high-energy photons to study the processes that Gorham and others are investigating.

Zipping by photons

Neutrinos, however, so rarely interact with any kind of matter that they zip right by the low-energy photons. And their electrically neutral nature prevents magnetic fields from deflecting or accelerating them. So neutrinos can preserve their original energy content - critical to determining their source.

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