Older star cluster found lurking near stellar nursery

Probing the plane of the Milky Way with a powerful orbiting telescope, scientists have found an elderly cluster of stars lurking surprisingly close to the plane of our galaxy, where such old star clusters are extremely rare.

“It’s like finding a fish out of water,” says Ed Churchwell, professor of astronomy who, with a team of scientists from UW–Madison, the University of Wyoming, Boston University, the Space Science Institute in Boulder, Colo., and the Spitzer Science Center discovered this rare cluster of stars with the aid of NASA’s Spitzer Space Telescope.

“We found something that’s not where it’s supposed to be,” he says.

Churchwell is the leader of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire, or GLIMPSE. The project is using the Spitzer Space Telescope to map the Milky Way in infrared light. Spitzer is one of the space-based telescopes that make up NASA’s Great Observatories program, which also includes the Hubble Space Telescope and the Chandra X-ray Telescope.

Among the oldest artifacts in the galaxy, globular clusters – very dense bundles of several hundred thousand stars – help to explain the life cycle of stars. The new finding will help scientists refine their ideas on how these very old clusters orbit the center of the Milky Way.

Researchers at the University of Wyoming-Laramie discovered the cluster while poring over data from the GLIMPSE project. The bright cluster of stars, fortuitously, is now passing through the plane of the Milky Way.

The cluster is new to astronomers, Churchwell says, because it is obscured by vast clouds of interstellar dust.

Unlike telescopes that gather light in visible wavelengths, the Spitzer Space Telescope explores the galaxy using infrared wavelengths, which are mostly unaffected by the dust particles that permeate interstellar space and absorb visible and ultraviolet light. Using optical wavelengths of light to look at the galaxy, says Churchwell, “is like looking at a scene through soot-covered glass. With Spitzer, you’ve wiped all that soot away, and you can see a lot more of what’s going on.”

GLIMPSE uses infrared light from Spitzer to create a more comprehensive picture of our pinwheel-shaped galaxy, especially the structure of the inner part as seen from Earth, which lies about 25,000 light years away. It also looks at the rate and dynamic qualities of star formation, the lifeblood of the galaxy.

“I’m expecting a lot of new discoveries to come out of the GLIMPSE survey,” Churchwell says.