SEATTLE - The most distant star cluster astronomers have ever
observed has been found behind one of the nearest clusters to Earth.
While using the Hubble Space Telescope to
study NGC 6397, a star cluster located only 8,500 light-years away, researchers
spotted a background elliptical galaxy whose light peeked through the nearby
cluster [image].
The distant galaxy contains
several hundred globular star clusters, each probably containing hundreds of
thousands of stars. The newfound galaxy
does not have a name yet.
"Often in these deep
images, one finds many distant galaxies, most of which will never have
names," said study team member Jason Kalirai, a postdoctoral fellow at the
University of California, Santa Cruz.
Kalirai and his colleague,
Harvey Richer of the University of British Columbia in Canada, followed up on
the Hubble images by analyzing the light signature of the distant clusters
using the Gemini South Telescope in Chile.
By measuring how much light
from the distant galaxy has been stretched during its journey across the
universe, a phenomenon called "redshift,"
the researchers determined that it was located about a billion light-years away,
making the star clusters in the galaxy some of the most distant ever studied.
"The largest
substantial population--say more than 100--of star clusters in any other galaxy
is located about 10 times closer than this object," Kalirai told SPACE.com.
The star clusters are so
far away, in fact, that they are about 10 million times dimmer than a single
giant star in NGC 6397. The findings were detailed here today at the 209th
meeting of the American Astronomical Society.
Clues about our own
galaxy
According to some theories,
globular star clusters are thought to provide the bulk needed to form elliptical
galaxies. The newly spied star clusters will provide scientists with a way to
test those theories.
"The
clusters can shed light on the evolution and formation of galaxies,"
Kalirai said. For example, astronomers can infer the ages and metal contents of
the stars in the clusters based on their colors. Combining this information
with the clusters' locations can tell astronomers when certain parts of the
galaxy formed.
"For
spiral galaxies like the Milky Way,
the globular clusters directly tell us when the halo
formed and, since this is the first component to form, when the galaxy itself
formed," Kalirai said in an e-mail interview.
The distant
galaxy could also provide a baseline for studying the evolution of clusters
in our own Milky Way.
"This
galaxy is far enough at a distance of 1 billion light-years that the light from
these clusters has taken a billion years to reach us," Kalirai explained.
"So, if all of these systems are old, then we are essentially probing
younger cousins of our own globular population."
Editor's
Note: All
week, SPACE.com is providing complete
coverage of the 209th meeting of the American Astronomical Society.
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