Sharper vision for eyes on the sky

Telescopes on Earth see like ones in orbit

January 08, 2002|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

WASHINGTON - A powerful new telescope technology is allowing astronomers to produce celestial images from the ground that are as sharp as those snapped by the orbiting Hubble Space Telescope.

Called adaptive optics, the new technology cancels out distortions caused by turbulence in Earth's atmosphere by changing the shape of the telescope's flexible mirror more than 1,000 times per second.

With a growing number of big mountaintop telescopes now fitted with adaptive optics, scientists say, there should be an acceleration in the search for knowledge about the formation of planetary systems like ours and for evidence that life has evolved around other stars.

"Adaptive optics is starting to open the floodgates on this type of discovery," said Ray Jayawardhana, a research fellow at the University of California at Berkeley, who led one of two studies using adaptive optics presented yesterday at the annual meeting of the American Astronomical Society.

Jayawardhana used the Gemini North telescope in Hawaii, with its giant 8.1-meter mirror. He produced high-resolution images of a newborn star 900 light-years from Earth, circled by a dusty disk that might one day evolve into a family of planets.

A second team of astronomers, led by Michael Liu at the University of Hawaii, used the Gemini North and Keck telescopes in Hawaii to snap a picture of a "brown dwarf" orbiting deep in the glare of a star much like our sun, 58 light-years from Earth.

A brown dwarf is a kind of failed star - too big to be called a planet, but too small to ignite and become a real star. Liu discovered this one orbiting closer to its star than Uranus is to our sun - the smallest separation of a brown dwarf and its companion star ever photographed.

"I think these discoveries are both marvelous," said astronomer Alan Boss of the Carnegie Institute of Washington, who was not involved in either study. "But in many ways, they are just tantalizing us for what is to come."

Adaptive optics technology was developed for military spy missions. It was declassified more than a decade ago, but has only recently become available to astronomers at some of the largest observatories.

Atmosphere bends light

The new technology addresses an old problem. Atmospheric turbulence bends starlight, producing the "twinkle" visible to the naked eye but blurring astronomers' photos of the stars.

To get above the distortions, astronomers built their telescopes on mountaintops and later launched them into space.

Adaptive optics solves the problem by precisely measuring the distortion in starlight as it strikes the telescope mirror. Then the system cancels out that distortion by using scores of tiny pistons to make continuous changes in the shape of the telescope's flexible secondary mirror.

A big telescope like Gemini North has more than three times the light-gathering power of Hubble, with its 2.4-meter mirror.

But even with adaptive optics, scientists say, such telescopes will never fully replace orbiting observatories, which are never idled by clouds or sunrise, and can "see" portions of the light spectrum that can't penetrate the atmosphere.

With the adaptive optics system in the new Gemini North telescope, Jayawardhana was able to zoom in on what had been a blurred pair of stars in ground-based photography, revealing what was actually a rare quadruple star system about 900 light-years from Earth.

Gemini also showed that one of the previously invisible young stars - barely 2 million years old - was surrounded by a narrow disk of dust three times the breadth of our solar system at the orbit of Pluto.

Beginning of planets

It's the kind of dusty disk that is believed to have condensed by the influence of gravity to assemble the planets of our solar system 4.5 billion years ago.

The thin, dark band of dust, Jayawardhana said, "is actually evidence that the dust grains have started to grow."

"The first tentative step in planetary formation has already started, which is pretty neat," he said.

Jayawardhana said the adaptive optics technology is already powerful enough to allow ground-based telescopes to photograph a young Jupiter-size planet orbiting a star like our sun.

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