  TALE OF TWO CLUSTERS YIELDS SECRETS 
  OF STAR BIRTH IN THE EARLY UNIVERSE
  PHOTO CAPTION  STScI-PR94-40
  FOR RELEASE: October 17, 1994

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 NGC1850, 
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 


ORIGINAL FILE NAME: NGC1850 (NASA SPACELINK)
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