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The Webfooted Astronomer - July 1999

 

Cerro Paranal's VLTs Revolutionize Observational Astronomy

by Laurie Goering, Chicago Tribune

From this mountaintop deep in the red Atacama desert at Cerro Paranal, Chile, Venus and Mars glow in a night sky thick with a billion stars of the Milky Way. The really impressive view of the heavens, however, is inside the bunker-like control room that processes images from VLT1, the first of the mountain's array of four giant telescopes.

On the computer screen, a brilliant white galaxy, shaped exactly like a sombrero with a gold rim of stars, appears in perfect detail. Another yellow-centered galaxy, some 100 million light years away, swirls with long reaching arms of blue stars, one arm fractured by the passing of another galaxy. What thrills astronomers, however, are the fainter celestial objects on the screen, indistinct circles of red light. These are galaxies 14 billion light years away, so far the fringes of the universe that they have never been seen before.

With one of the new VLTs—Very Large Telescopes—at Cerro Paranal, astronomers can find thousands of such objects in a night. When all four telescopes are linked together, using interferometry, researchers will be able to look 10,000 times further into the universe than ever before possible.

"This telescope will change astronomy as a science," says Jason Spyromilio, a Greek supernova researcher and one of the staff astronomers at Cerro Panal. "It's the most amazing thing I've every used." Already, using just one of the telescopes, scientists have found strong evidence that the universe will continue expanding.

With the four telescopes working together—two are now online—they will be able to peer for the first time into the mouth of black holes. The will be able to distinctly see planets in other solar systems and to spot the first stars and galaxies ever born in the universe.

"We want to see the first stars shining," says Massimo Tarenghi, the Italian director of the observatory. "This will be a totally new domain."

The telescopes, the largest in the world and the first of their design, are a $700-million project of the European Southern Observatory, a coalition of eight European nations who also run a smaller observatory in the Chilean desert, near La Serena.

Each has an 8.2-meter diameter ceramic mirror, about as thick as the length of a dollar bill, coated with a thin polish of aluminum. The use of ceramics is a breakthrough, as an equivalent traditional glass mirror would weigh 115 tons and be a yard thick, impossible to move. These mirrors, however, move with precision measured in microns thanks to a supporting bed of 150-computer driven pistons. The whole 500-ton telescope floats on a hydrostatically charged layer of oil. Without gears or ball bearings to create friction, a single person can start the giant telescope rotating with just a push.

"The difficulty is to stop it," jokes Marco Quattri, the telescope's Italian designer. The instrument "will be the standard in its class for the next 20 years," he says.

Just as impressive as the telescope, however, is the concrete and steel tunnel that links them. When all four big telescopes and three smaller auxiliary telescopes are operating—the whole network will be completed by 2003—it will be possible to point them all at the same object and simultaneously beam the light rays into the tunnel. There, mirrors will reflect the images and combine them into a single beam of light, turning the four 8.2-meter telescopes into the equivalent of one 200-meter scope. The system also will use adaptive optics to correct for atmospheric distortion.

Chile's northern Atacama desert, a barren rocky landscape that could be the surface of Mars is one of the best places on Earth to stare at the stars. It is dark—Antofagasta, the nearest city, lies 75 miles away and even the white construction trailers that serve as a temporary home for Cerro Paranal's staff are hidden tight against the base of the mountain, out of view of the telescopes. Eventually researchers plan to build a permanent living complex entirely underground, complete with hotel, swimming pool, and domed gardens.

The flattened peak of the mountain--its top shaved off to ground the telescopes on bedrock--lies just seven miles from the Pacific Ocean, to take advantage of the smooth layers of air rising from the sea. A near-permanent high pressure system and the Andean and coastal mountain ranges on either side of the Atacama holds clouds below the 8500-foot summit and stops rain. In this driest desert on Earth, less than half an inch of rain falls every 10 years. The desert's only equivalent in astronomical desirability is Mount Kea, a 13,000-foot peak in Hawaii, the favored viewing site for the northern hemisphere sky.

Both locations have been at the heart of a revolution in astronomy in recent years that has seen the building of a new generation of huge high-tech telescopes, such as Caltech's Keck and Japan's Subaru in Hawaii, and the Carnegie Institute’s twin Magellan instruments in Chile's desert. Now, scientists are for the first time talking of instruments as large as 100 meters. "It's mind boggling, overwhelming," says Rober Gilmozzi, and astronomer at Cerro Paranal, who is already working on the European Observatories next project, OWL, or Overwhelmingly Large Telescope, a 100-meter instrument that will stand half as tall as the Eiffel Tower and cost $1 billion.

For now, the VLTs on Cerro Paranal are a revolution in themselves, the most powerful telescope array on earth even with just two of four instruments operating. The first telescope opened April 1 for outside scientific studies and 800 researchers are already clamoring for time.

As the sun sets at Cerro Paranal and a cold wind whips across the mountaintop, the doors of VLT1 glide slowly open, their polished silver reflecting the brilliant orange sunset and the blue shadows settling over the desrt. Silently the telescope glides into position for its first observation of the night, a distant cloud of red gas emitted by a supernova.

© Chicago Tribune. Reprinted by permission.

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