Gamma-ray detection in space only for the swift

If the race goes to the swift, then Neil Gehrels's spacecraft has the look of a winner in the beat-the-clock race to observe the most powerful explosions the universe can serve up - gamma-ray bursts.

On Monday, the National Aeronautics and Space Administration gave its final nod to Dr. Gehrels' project, which is scheduled for launch in 2003.

Named for a bird that flies for years at a time rarely landing on the ground, the SWIFT spacecraft is designed to automatically detect and locate the bursts, then train a pair of on-board, European-donated telescopes on them in roughly one minute.

With one telescope covering x-rays and the other ultraviolet light, the craft will be able to track a good portion of a burst's evolution almost from the time it detonates.

SWIFT also will be able to pin down a burst's location with much greater precision than anything else, allowing other space-and ground-based instruments to follow the explosion's evolution as its light shifts into the visible and infrared range. And the craft's gamma-ray detectors are designed to spot bursts over a much broader range of the gamma-ray spectrum, which should greatly increase the number researchers will be able to study, Gehrels says.

First discovered some 30 years ago by satellites designed to detect nuclear explosions on Earth, gamma-ray bursts have captured the imaginations of astrophysicists worldwide.

Awed by the vast amounts of energy these explosions release, scientists want to learn how they happen and perhaps use them to trace the history of star formation in the early universe. "These are mindboggling explosions," says Gehrels, an astrophysicist at the Goddard Space Flight Center and the lead investigator on the mission. "It's as though you've converted the rest mass of the sun into gamma-rays in a few seconds."

From 1991 to 1999, NASA's Compton Gamma Ray Observatory detected some 2,000 bursts spread randomly around the sky. But the craft's instruments lacked the ability to truly pinpoint their location. In 1996, the European Space Agency launched its BeppoSAX spacecraft, which carried gamma-ray and x-ray instruments.

As a result, it not only could detect bursts, but nail down their positions accurately enough so other telescopes could watch as well. BeppoSAX's observations stunned researchers, because they helped establish that these events were happening at distances half way to the edge of the universe, not within our galaxy, as some previously thought.

Information from SWIFT will allow astrophysicists to test ideas about why these explosions occur. The leading candidate, Gehrels says, holds that gamma-ray bursts are triggered when the outward pressure from a supermassive star's radiation can't withstand the inward tug of the star's gravity. In an instant, the superstar collapses into a black hole, releasing energy as an intense burst of gamma rays.

(c) Copyright 2001. The Christian Science Publishing Society

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