|Newfound Star Cluster May Be Final Milky Way 'Fossil'||
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 our Milky Way galaxy, 13 or so billion
years ago. They are sprinkled around the center of the galaxy
like seeds in a pumpkin. Astronomers use clusters as tools for
studying the Milky Way's age and formation.
Image above: On the left, a visible-light image shows a dark sky speckled with stars. On the right, in the same patch of sky, a false-color image taken by NASA's Spitzer Space Telescope shows a globular cluster previously hidden in the dusty plane of our Milky Way galaxy. + Click for larger image.
Image coutesy: NASA/JPL-Caltech/University of Wyoming/2MASS/DSS.
New infrared images from NASA's Spitzer Space Telescope and the
University of Wyoming Infrared Observatory reveal a never-
before-seen globular cluster within the dusty confines of the
Milky Way. The findings will be reported in an upcoming issue
of the Astronomical Journal.
"It's like finding a long-lost cousin," said Dr. Chip
Kobulnicky, a professor of physics and astronomy at the
University of Wyoming, Laramie, and lead author of the report.
"We thought all the galaxy's globular clusters had already been
"I couldn't believe what I was seeing," said Andrew Monson, a
graduate student at the University of Wyoming, who first
spotted the cluster. "I certainly wasn't expecting to find such
The newfound 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 our galaxy, having formed about
10 to 13 billion years ago. They contain several hundred
thousand stars, most of which are older and less massive than
Monson first noticed the 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 our 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 Dr. Michael Werner of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., 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 the University of Wyoming Infrared
Observatory helped set the distance of the new cluster at about
9,000 light-years from Earth - closer than most clusters --
and set the mass at the equivalent of 300,000 Suns. The
cluster's apparent size, as viewed from Earth, is comparable to
a grain of rice held at arm's length. It is located in the
The research team consists of astronomers from the University
of Wisconsin, Madison; Boston University, Boston, Mass.; the
University of Maryland, College Park, Md.; the University of
Minnesota, Twin Cities; the Space Science Institute, Boulder,
Colo.; 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 Dr. Ed
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
NASA's Jet Propulsion Laboratory
University of Wyoming, Laramie, Wyo.