Science + Technology

Astronomers Use Laser to Take Clearest Images of the Center of the Milky Way


UCLA astronomers andcolleagues have taken the first clear picture of the center of our Milky Waygalaxy, including the area surrounding the supermassiveblack hole, using a new laser virtual star at the W.M. Keck observatory in Hawaii.

"Everything ismuch clearer now," said Andrea Ghez, UCLA professorof physics and astronomy, who headed the research team. "We used a laser toimprove the telescope's vision — a spectacular breakthrough that will help us understand theblack hole's environment and physics. It's like getting Lasik surgery for theeyes, and willrevolutionize what we can do in astronomy."

Astronomers are used to working withimages that are blurred by the Earth's atmosphere. However, a laser virtualstar, launched from the Keck telescope, can be used to correct the atmosphere'sdistortions and clear up the picture. This new technology, called Laser Guide Star adaptive optics, will lead to important advances for thestudy of planets in our solar system and outside of our solar system, as well asgalaxies, black holes, and how the universe formed and evolved, Ghez said.

"We have workedfor years on techniques for 'beating the distortions in the atmosphere' andproducing high-resolution images," she said. "We are pleased to report the first Laser Guide Star adaptiveoptics observations of the center of our galaxy."

Ghez and her colleagues took "snapshots" ofthe center of the galaxy, targeting the supermassiveblack hole 26,000 light years away, at different wavelengths. This approach allowed them to study the infrared lightemanating from very hot material just outside the black hole's "event horizon,"aboutto be pulled through.

"Weare learning the conditionsof the infalling material and whether this plays arole in the growthof the supermassive black hole," Ghezsaid. "The infrared lightvaries dramatically from week to week, day to day and even within a singlehour."

The research,federally funded by the National Science Foundation, will be published Dec. 20 in the Astrophysical Journal Letters.

The researchwas conducted using the 10-meter Keck II Telescope, which is the world's first10-meter telescope with a laser on it. Laser Guide Star allows astronomers to"generate an artificial bright star" exactly where they want it, which revealsthe atmosphere's distortions.

Since 1995, Ghez has been using the W.M. Keck Observatory to study thegalactic center and the movement of 200 nearby stars.

Blackholes are collapsed stars so dense that nothing can escapetheir gravitational pull, not even light. Black holes cannot be seendirectly, but their influence on nearby stars is visible, and provides asignature, Ghez said. The supermassive black hole, with a mass more than 3 milliontimes that of our sun, is in the constellation of Sagittarius. Thegalactic center is located due south in the summer sky.

The black hole came intoexistence billions of years ago, perhaps as very massive stars collapsed at theend of their life cycles and coalesced into a single, supermassiveobject, Ghez said.

Co-authors onthe research include UCLA graduate students Seth Hornsteinand Jessica Lu; the adaptive optics team at W. M. Keck Observatory: David Le Mignant, Marcos Van Dam and Peter Wizinowich;Antonin Bouchez (formerlywith the W. M. Keck Observatory) and Keith Matthews at Caltech; Mark Morris, aUCLA professor of physics and astronomy; and Eric Becklin,a UCLA professor of physics and astronomy.

Ghez provides moreinformation, and images of the galactic center, at



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