Figure 1
Figure 2
This 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. Globular clusters are compact bundles of old stars that date back
to the birth of our galaxy, 13 or so billion years ago. Astronomers use
these galactic "fossils" as tools for studying the age and formation of
the Milky Way.
Most clusters orbit around the center of the galaxy well above its
dust-enshrouded disc, or plane, while making brief, repeated passes
through the plane that each last about a million years. Spitzer, with
infrared eyes that can see into the dusty galactic plane, first spotted
the newfound cluster during its current pass. A visible-light image
(inset of Figure 1) shows only a dark patch of sky.
The red streak behind the core of the cluster is a dust cloud, which may
indicate the cluster's interaction with the Milky Way. Alternatively,
this cloud may lie coincidentally along Spitzer's line of sight.
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
constellation Aquila.
Astronomers believe that this cluster may be one of the last in our galaxy
to be uncovered.
This image composite was taken on April 21, 2004, by Spitzer's infrared
array camera. It is composed of images obtained at four wavelengths: 3.6
microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns
(red).
Galactic Fossil Found Behind Curtain of Dust
In Figure 2, the image mosaic shows the same patch of sky in various
wavelengths of light. While the visible-light image (left) shows a dark
sky speckled with stars, infrared images (middle and right), reveal a
never-before-seen bundle of stars, called a globular cluster. The left
panel is from the California Institute of Technology's Digitized Sky
Survey; the middle panel includes images from the NASA-funded Two Micron
All-Sky Survey and the University of Wyoming Infrared Observatory (circle
inset); and the right panel is from NASA's Spitzer Space Telescope.
The Two Micron All-Sky Survey false-color image was obtained using
near-infrared wavelengths ranging from 1.3 to 2.2 microns. The University
of Wyoming Observatory false-color image was captured on July 31, 2004,
at wavelengths ranging from 1.2 to 2.2 microns. The Spitzer false-color
image composite was taken on April 21, 2004, by its infrared array camera.
It is composed of images obtained at four mid-infrared wavelengths: 3.6
microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns
(red).
