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PHOTO CAPTION STScI-PR94-40
FOR RELEASE: October 17, 1994

TALE OF TWO CLUSTERS YIELDS SECRETS
OF STAR BIRTH IN THE EARLY UNIVERSE

This NASA Hubble Space Telescope (HST) image shows rich detail,
previously only seen in neighboring star birth regions, in a pair of
star clusters 166,000 light-years away in the Large Magellanic Cloud
(LMC), in the southern constellation Doradus. The field of view is
130 light-years across and was taken with the Wide Field Planetary
Camera 2.

HST's unique capabilities -- ultraviolet sensitivity, ability to see
faint stars, and high resolution -- have been utilized fully to identify
three separate populations in this concentration of nearly 10,000
stars down to the 25th magnitude (more that twice as many as
can be seen over the entire sky with the naked eye on a clear night
on Earth). The field of view is only 130 light-years across. Previous
observations with ground-based telescopes resolve less than 1,000
stars in the same region. About 60 percent of the stars belong to the
dominant yellow cluster called NGC 1850, which is estimated to be
50 million years old. A scattering of white stars in the image are
massive stars that are only about 4 million years old and represent
about 20 percent of the stars in the image. (The remainder are field
stars in the LMC.) Besides being much younger, the white stars are
much more loosely distributed than the yellow cluster. The
significant difference between the two cluster ages suggests
these are two separate star groups that lie along the same line
of sight. The younger, more open cluster probably lies 200
light-years beyond the older cluster. If it were in the foreground,
then dust contained in the white cluster would obscure stars in
the older yellow cluster.

To observe two well-defined star populations separated by such
a small gap of space is unusual. This juxtaposition suggests that
supernova explosions in the older cluster might have triggered the
birth of the younger cluster.

This color composite image is assembled from exposures taken in
ultraviolet, visible, and near-infrared light. Yellow stars correspond
to Main Sequence stars (like our Sun) with average surface temperatures
of 6000 Kelvin; red stars are cool giants and supergiants (3500 K); white
stars are hot young stars (25,000 K or more) that are bright in ultraviolet.


Credit: R. Gilmozzi, Space Telescope Science Institute/European Space
Agency; Shawn Ewald, JPL; and NASA