| 
Credit: Leigh Jenkins, Ann Hornschemeier   
(Goddard   
Space Flight Center)   
et al.,   
JPL-Caltech, SDSS, NASA
Explanation:
In visible   
light images, over a thousand galaxies are seen to   
lie within a volume about 20 million light-years across in   
the rich Coma Galaxy Cluster.   
   
But infrared images of the Coma Cluster have now been used   
to add thousands more to the Coma's galaxy count in the form   
of previously   
undiscovered dwarf galaxies.   
   
This composite combines infrared   
Spitzer Space Telescope image data   
(red and green) with visible light Sloan Sky Survey data (blue)   
for the central part of the cluster.   
   
Over 1 degree wide, the field is   
dominated by two giant   
elliptical galaxies in blue.   
   
Still, many of the small green smudges (see magnified inset)   
are identified as dwarf galaxies,   
roughly comparable to the   
Small Magellanic Cloud.   
   
Dwarf galaxies are thought to form   
first, providing building blocks for larger galaxies.   
   
The well-studied,   
friendly,   
Coma Cluster   
is 320 million light-years away.    
   
JPL-Caltech, SDSS, NASA
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Based on Astronomy Picture
Of the Day
Publications with keywords: galaxy cluster - dwarf galaxy
Publications with words: galaxy cluster - dwarf galaxy
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