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Stars Untwinkled

Earth's atmosphere makes for a dancing, distorted image, and that's a problem for astronomers. Enter the art of adaptive optics.


Since the days of Galileo, astronomers have been plagued by one consistent drawback: the Earth's atmosphere. Starlight can travel undisturbed through empty space for hundreds of light-years. But in the last few nanoseconds before it hits Earth and its telescopes, the light gets distorted by swirling winds and air currents.

"It gives you a very fuzzy, dancing image," said Fred Chaffee, who directs the world's largest telescope, the Keck, and has long been frustrated by the inability of the powerful machine to create sharper images. "The reason stars twinkle is because of the atmosphere."

Now, four centuries after Galileo lifted his handmade "spyglasses" toward the moons of Jupiter, astronomers have a high-tech fix for their earthbound telescopes. Adaptive optics systems look at guide stars to measure atmospheric distortions. The system then uses those measurements to change the shape of a mirror that can be bent up to a thousand times per second to correct for the rapid fluctuations of the atmosphere.

"It's like putting eyeglasses on a telescope," said Andrea Ghez, a UCLA astronomer who is using adaptive optics to probe a supermassive black hole that appears to reside at the center of the Milky Way.

Los Angeles Times Tuesday January 29, 2002 Home Edition Main News Part A Page 2 A2 Desk 1 inches; 21 words Type of Material: Correction
Graphic credit--The graphic appearing on the Science File page in Section A on Monday was missing the credit line. The graphic was by Leslie Carlson.
Los Angeles Times Friday February 8, 2002 Home Edition Main News Part A Page 2 A2 Desk 2 inches; 38 words Type of Material: Correction
Keck telescope mirror--A story about adaptive optics in Section A on Jan. 28 incorrectly referred to astronomer Jerry Nelson as the designer of the Keck telescope's 30-meter mirror. Nelson is working on a 30-meter mirror, but the mirror he designed for Keck is 10 meters.
Los Angeles Times Friday March 22, 2002 Home Edition Main News Part A Page 2 A2 Desk 1 inches; 30 words Type of Material: Correction
Laser photo--A photograph of the Keck Observatory laser that ran in editions of Jan. 28 was credited incorrectly. The photo should have been credited to John McDonald and the Canada-France-Hawaii Telescope Corp.

Ghez's work requires measuring the stars rotating around the edge of the black hole. "You just can't see the stars without adaptive optics," she said. "And if you can't see the stars, you can't do the work."

The idea to correct telescopes was first proposed by California astronomer Horace Babcock in the 1950s. The military developed some of the technology in its "Star Wars" program and declassified it in 1991. High-speed computing, the development of glass mirrors so thin they can be easily deformed and a lot of hard work in recent years have made it a reality.

"It's actually very hard to do," said Jerry Nelson, the designer of Keck's 30-meter mirror and the director of the Center for Adaptive Optics, a National Science Foundation center based at UC Santa Cruz. "It's a very sophisticated procedure."

The first adaptive optics systems have been in place on some of the world's biggest telescopes, including Keck and Gemini on Mauna Kea, Hawaii, for less than two years. Already, the system has produced impressive results, including several highlighted this month when astronomers gathered for their annual meeting in Washington, D.C.

UC Berkeley astronomer Imke de Pater has been using adaptive optics to look at objects closer to home--the planets in our solar system. Adaptive optics has been able to focus images of Neptune to such an extent that the images are as good or better than those taken by spacecraft flying by the planet, she said.

She has been able to make out storms in Neptune's atmosphere, suggesting mysterious activity on a body that was previously seen as something of a planetary dud.

Another victory for adaptive optics came in 1999, when astronomers turned Keck toward Io, one of the moons of Jupiter, because the night was too cloudy to observe more distant objects. They happened to catch a volcano in the act of erupting. In an image unblurred by adaptive optics, the volcano was a large, bright blip on the edge of the moon.

Ray Jayawardhana, a research fellow at UC Berkeley, is trying to understand the details of how planets form from the dusty disks that surround young stars. Using adaptive optics on the 8.2-meter Gemini telescope, he led a team that captured an image of a protoplanetary disk circling an extremely young star. The image was so detailed, the team could infer the shape of the disk and the size of dust particles within it--particles that could one day grow into planets like Earth.

Astronomers are now racing to capture an image of a Jupiter-sized planet circling a young star. Jupiter-like planets have been detected indirectly by other astronomers, but no images have been captured because current telescopes had not been able to discern the dimmer planets from the bright stars they orbit. "It's possible now only because of adaptive optics on large telescopes," Jayawardhana said.

Space telescopes such as Hubble avoid the vagaries of the atmosphere by orbiting above it, but they are costly to build and maintain and therefore much smaller than telescopes on the ground, limiting their use for tasks such as planet hunting.

A UCLA team used adaptive optics to probe some of the most distant reaches of the universe in a hunt for young galaxies that could help explain how galaxies evolve. Because adaptive optics systems require a guide star to correct fluctuations in the atmosphere, the team could probe only areas of the sky that were near relatively bright stars.

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