12 January 2002
Astronomers have taken the first sharp pictures of downtown Milky Way the center of our home galaxy. From our place in the galactic suburbs 26,000 light years away, they find a surprisingly chaotic, roiling panorama of star birth and death, producing superheated gas clouds whose source has long been a mystery. The research suggests that the churning that occurs there affects us way out here.
At millions of degrees, the center of the Milky Way might be a nice place to visit by telescope, but you wouldn't want to go there.
A telescope visit is just what University of Massachusetts astronomers took. They went on a virtual tour of the region with the U.S. space agency's orbiting Chandra X-ray Observatory. To their surprise, they discovered what a busy metropolis it is.
"We have made the highest resolution, most detailed image of the galactic center," says team member Cornelia Lang, speaking at the American Astronomical Society conference in Washington. Ms. Lang notes that the Milky Way's center appears blurry to optical telescopes on the ground because of intervening dust, gas, and star glare.
But x-rays penetrate all this, and the Chandra Observatory was designed to be powerful enough to bring distant x-ray sources into focus. "So the previous images were very low resolution and didn't give us any clue as to what the nature of the x-ray emission was in the galactic center," she says. "Our image for the first time shows distinct components of x-ray emission. We've seen 1,000 point sources. Previously, there were only 20 x-ray point sources known."
The color of these sources suggests they are a large collection of star remnants, dying stars known as white dwarfs; collapsed stars called neutron stars; and black holes, which are denser collapsed stars with gravity so strong that even light cannot escape.
Pervasive among these bodies is a brighter, but diffuse hot x-ray gas arising from the recent formation of massive stars.
University of Massachusetts astronomer Daniel Wang says the picture portrays an intensely active region of star birth and death, a busier area of star transition than where we are nearer the edge of the Milky Way. "There are tons of massive stars forming in the galaxy center," he says.
At the University of Cologne in Germany, astrophysicist Andreas Eckart says the images are interesting not only for what they say about our Milky Way, but also what they may imply about the millions of galactic centers much further away. "Galactic nuclei are of great importance because those are the most distant objects that we actually can investigate if we talk about the evolution of our universe," he says. "The nucleus of our own galaxy is the one that is closest to us and probably all the physical processes that we are able to study there also apply to other nuclei."
The new Chandra observatory map shows that the hot gas at the Milky Way's center seems to be escaping to the galaxy's edges, like steam from a teakettle. This stellar wind contains carbon, iron, and all the other elements forged within stars from which we, the planets, and other celestial objects are made. Therefore, this outflow is apparently is a distribution mechanism to enrich the rest of the galaxy, including our solar system.
Daniel Wang calls it a galactic ecosystem. "So what happens in one part of the galaxy, especially the center of our galaxy, might influence the rest of the galaxy," he says.
The Chandra Observatory Mr. Wang's team used for its work was launched from a U.S. space shuttle in 1993. It is named in honor of the late Indian-American Nobel Prize winner Subrahmanyan Chandrasekhar of the University of Chicago.