Experts Try to ‘De-Twinkle’ Stars to Help Astronomers

It may seem unromantic to stamp out the twinkling of the stars, but astronomer Samuel Durrance doesn’t think so.

“In order to study them, about their mysteries, we have to be able to see them better,” Durrance said. “We’re trying to see their true beauty.”

Durrance leads a Johns Hopkins University team working on adaptive optics technology, which uses mirrors, sensors and computers to reduce the atmospheric distortion that makes stars seem to dance. “Much like lying at the bottom of a pool and looking at an object being dangled above you the water distorts the image of what you see quite severely. . . . The twinkling is not an aspect of the stars but an aspect of the atmosphere.”

Scientists at other institutions are developing similar instruments. By making it easier to examine material around stars, they may bring astronomers closer to an elusive goal--discovering planets outside our solar system.

Scientists theorize that material left after a star has formed falls into a stable orbit around it and coalesces over millions of years into planets.

The Johns Hopkins instrument won’t allow astronomers to directly see possible planets but could let them measure changes in the brightness around a star, possible evidence of planets, said researcher Mark Clampin.

The instrument, an adaptive optics coronagraph, uses two mirrors, sensors and a high-speed computer to manipulate light waves entering a telescope. One mirror is a thin membrane whose contours can be changed as often as 100 times a second to compensate for the motion of a star’s image. The other, called a flat mirror, wobbles 100 times a second to eliminate the distortion of light rays as they strike the telescope lens.

Only the flat mirror was tested during observations in May of Beta Pictoris, a star 312 trillion miles away, at an observatory in Las Campanas, Chile. The entire system is expected to be ready in about two years.

A complete system already is in use at the National Optical Astronomy Observatories in Tucson. Astronomer Larry Goad said it is one of two started in anticipation of the next generation of ground-based telescopes.

The new telescopes, which will be about eight meters in diameter instead of the customary two to five meters, will need help correcting distortions in the larger amount of light they can gather.

Devices Experimental

Goad said adaptive optics devices are considered experimental at this point because nobody except their creators can figure out how to operate them.

Astronomers at UC Berkeley also have an experimental system in the works. And a related development at the University of Illinois is the invention of laser-generated artificial stars. An artificial star can provide the “guide star” scientists need to calibrate adaptive optics equipment properly, electrical engineer Chet Gardner said.

Artificial stars, formed with a yellow-orange laser beam that illuminates a spot in a layer of sodium particles about 60 miles high, can compensate for the usual lack of a bright object in the sky near the object under study.

“In order to do this de-twinkling, one needs a very bright object or a reference point that is very bright . . . so you can deform the mirror to correct the distortion,” Gardner said. “This star works just as well as an actual star that may be millions of miles away.”

The Hopkins instrument was designed in part to get a better look at an unusual disk around Beta Pictoris, which was detected several years ago by its infrared emissions, Clampin said. It is too soon to know what the observations in Chile will yield. Images of the Beta Pictoris disk, containing matter that could be planets or material that will form planets, are being enhanced.

“It’s hard to predict revolutions,” Durrance said. “It’s certainly going to have an impact, and I think it will have a major impact when we can eliminate the effects of the distortion.”