UW ASTRONOMERS DISCOVER STAR CLUSTER

Oct. 12, 2004 -- New infrared images from NASA's Spitzer Space Telescope and the University of Wyoming Infrared Observatory (WIRO) have revealed a never-before-seen globular cluster within the dusty confines of the Milky Way. The findings will be reported in a forthcoming issue of the Astronomical Journal.

Just when astronomers thought they might have dug up the last of our galaxy's "fossils," they've discovered a new one in the galactic equivalent of our own backyard.

Called globular clusters, these ancient bundles of stars date back to the birth of the Milky Way, 13 or so billion years ago.

"It's like finding a long lost cousin," said Chip Kobulnicky, a professor in the UW Department of Physics and Astronomy and lead author of the new paper. "We thought all the galaxy's globular clusters had already been found."

"I couldn't believe what I was seeing," said Andrew Monson, a graduate student at UW who first spotted the cluster. "I certainly wasn't expecting to find such a cluster."

The new cluster is one of about 150 known to orbit the center of the Milky Way. These tightly-packed knots of stars are among the oldest objects in the galaxy. They contain several hundred thousand stars, most of which are older and less massive than our sun. Astronomers use clusters as laboratories for studying the age and formation of our galaxy.

Monson first noticed the new cluster while scanning data from the Spitzer Space Telescope's Galactic Legacy Infrared Mid-Plane Survey Extraordinaire -- a survey to find objects hidden within the dusty mid-plane of the galaxy. He then searched archival data for a match and found only one undocumented image of the cluster from a previous NASA-funded infrared survey of the sky, called the Two Micron All-Sky Survey. "The cluster was there in the data but nobody had found it," said Monson.

"This discovery demonstrates why Spitzer is so powerful -- it can see objects that are completely hidden in visible light," said Michael Werner, project scientist for Spitzer. "This is particularly relevant to the study of the plane of our galaxy, where dust blocks most visible light."

Follow-up observations with WIRO helped set the distance of the new cluster at about 9,000 light-years from Earth -- close as far as clusters go -- and the mass at the equivalent of 300,000 suns. Monson says the cluster's apparent size, if viewed from Earth, is comparable to a grain of rice held at arm's length. It is located in the constellation Aquila.

The research team includes astronomers from the University of Wisconsin, Madison; Boston University, Boston, Mass.; the University of Maryland, College Park; the University of Minnesota, Twin Cities; and the Spitzer Science Center, Pasadena, Calif. The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire is managed by the University of Wisconsin and led by Ed Churchwell.

The Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology. JPL is a division of Caltech. Spitzer's infrared array camera, which captured the new cluster, was built by NASA Goddard Space Flight Center, Greenbelt, Md. The camera's development was led by Giovanni Fazio of Harvard-Smithsonian Center for Astrophysics.

Additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu. Additional information about the University of Wyoming Infrared Observatory is available at http://physics.uwyo.edu/~mpierce/WIRO/.