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If quasars could talk: a telescope to help tell their stories

Infrared observatory, set to launch this Monday, may yield insights into universe.

After a four-month delay, the US is set to loft the last in a set of orbiting observatories that are revolutionizing humanity's understanding of the universe.

If all goes as planned, Monday morning, the National Aeronautics and Space Administration (NASA) will launch the one-ton Space Infrared Telescope Facility (SIRTF) from Florida's Kennedy Space Center. It's the final piece of NASA's Great Observatory series, which includes the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-Ray Observatory. [Editor's note: The original version of this article gave the wrong date for the planned launch of the one-ton Space Infrared Telescope Facility.]

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Operating at infrared wavelengths, the $1.19-billion observatory is expected to lift the veil of dense dust and gas that obscures the earliest birth throes of stars and planets. In addition, researchers say they'll track the evolution of galaxies from the universe's earliest epochs; study cold, dark clouds of dust and gas that breed stars and solar systems; and uncover the nature of the debris that orbits the sun beyond Pluto and is thought to be detritus left over from the solar system's formation.

SIRTF's greatest contribution, however, may come as its data are analyzed alongside results from the other observatories, covering different wavelengths of light.

"We gain an enormous amount by studying objects over a broad range of wavelengths," says Charles Beichman, chief scientist for astronomy and physics at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

For example, SIRTF will likely bring leaps in quasar knowledge, notes Belinda Wilkes, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Quasars "are the brightest sources in the universe and they're bright at many wavelengths," from radio waves through gamma rays. "But to get the full picture ... we need to look in the infrared - one of the biggest holes in our knowledge."

Quasars' brilliance is believed to be driven by supermassive black holes at the center of distant young galaxies. As matter falls into the black holes' gravitational grasp, it collides with other in-falling matter, radiating energy. But that region of collision, known as the accretion disk, is relatively tiny - and, when appearing edge-on to astronomers, is hard to spot in visible and ultraviolet wavelengths.

The region of highest infrared emission, however, is thought to originate in a doughnut-shaped structure of gas and dust from 10 to 100 light-years across, with the black hole at its center. So as astronomers study quasar populations, infrared data do more than reveal processes behind a quasar: The much larger size of these regions may tip them off to quasars they'd otherwise miss. "For the first time, we will be able to see quasars regardless of viewing angle," Dr. Wilkes says.

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Unlike Hubble, which has seen increasing competition from ground-based telescopes as technologies have cut down the "twinkle" induced by Earth's atmosphere, SIRTF's work can be done only from orbit. Even at night, Earth's atmosphere appears daylight-bright across most of the infrared wavelengths. The atmosphere has a few slim "windows" allowing a few wavelengths for infrared observations. But these do little more than tantalize astronomers.

Indeed, Earth and the moon are such "hot" infrared sources that SIRTF will orbit the sun instead. The observatory will trail Earth by an additional 9.3 million miles each year to ensure that its cooling system has as little competition as possible. The goal is to increase "mileage," stretching the mission from 2-1/2 years to five. That would allow for more overlapping observations with Hubble and Chandra - a confluence of data that astrophysicists crave.

Already, orbiting observatories "are forcing astronomers to rewrite the textbooks," says Stephen Maran, spokesman for the American Astronomical Society.

The Hubble Space Telescope has been key in refining estimates for the age of the universe, he says. It was also critical in discovering "dark energy," a force that seems to be accelerating the universe's expansion. The Compton Gamma-Ray Observatory caught the first glimpse of a cloud of antimatter near Milky Way's center. And Chandra found evidence for a black hole long thought to lie at the Milky Way's core.

But the series is rewriting more than textbooks, notes John Bahcall, a Princeton astrophysicist: It's changed astronomers' approach. "We now know that to understand nature we have to look in all the possible wavelengths. This has dissolved fences between branches of the subject and made all of us much broader in our thinking and in our techniques," he says.

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