On a clear night, a broad band of stars sweeps across the sky, backed by the faint, milky glow of even more stars. This is the Milky Way and on a midsummer eve the very center of it can be picked out within the Sagittarius constellation. But even on the clearest night, the earth's atmosphere obscures the true brilliance of our galaxy and astronomers have long struggled with images blurred by its mix of gases and turbulence. Now researchers have used a new laser-generated star to obtain the clearest pictures yet of the Milky Way's center.
Astronomer Andrea Ghez of the University of California, Los Angeles, and her colleagues used the 10-meter Keck 2 telescope in Hawaii, which has a laser attached to it, to observe our galaxy. The skywatchers employed the 14-watt laser to generate a fake star. By continuously imaging this false star along with the real ones, they could correct any fuzziness or other distortions introduced by the earth's atmosphere. "We used a laser to improve the telescope's vision," Ghez explains. "It's like getting LASIK surgery for the eyes, and will revolutionize what we can do in astronomy."
Ghez trained the telescope on the very center of the Milky Way in July 2004, taking pictures with an infrared camera of the supermassive black hole thought to lie there. The clarity provided by the laser allowed her team to distinguish between nearby stars and the infrared emanations of some mysterious, very hot material. This fuzzy warmth from the galactic center has puzzled scientists for 30 years and clearer observation of it has led Ghez and her collaborators to conclude that it is most likely superheated interstellar dust on the verge of falling into the black hole in the paper presenting their findings in the current issue of Astrophysical Journal Letters. "We are learning the conditions of the infalling material and whether this plays a role in the growth of the supermassive black hole," Ghez says. "The infrared light varies dramatically from week to week, day to day and even within a single hour."
The variations in such emissions could arise from particular events that generate stronger flares, the researchers speculate. Whatever the case, the false star should help guide further observation of the riddle at the center of our galaxy. "We have worked for years on techniques for beating the distortions in the atmosphere," Ghez notes. "We are pleased to report the first laser guide star adaptive optics observations of the center of our galaxy."