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NASA/Chandra/Palomar Obs.
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A compact group of galaxies known as Stephan's Quintet was nearly demoted to a quartet recently, but as you'll soon learn, its status has remained intact.
This unusual photo of the group combines X-ray and optical observations into one image to better illustrate the dynamics of the system. Blue areas represent X-ray observations of gas heated by shock to about 10.8 million degrees Fahrenheit (6 million Celsius).
The heat is produced by the rapid motion of a spiral galaxy that is intruding on the system (it's labeled B in the wider-field optical image at the bottom right -- you'll need to enlarge the image to see the labels). As galaxies move through the hot gas and are affected by the gravity of each other, cool gas is stripped out of them. This deprives the galaxies of raw material needed to form new stars.
The group is about 280 million light-years from Earth.
When the image was released earlier this month, astronomers said the galaxy marked F is actually in the foreground, closer to Earth and not part of the quintet, as previously thought. Galaxy C, however, has now been found to be in the group, so it is still a quintet.
The spiral galaxies will probably become elliptical galaxies in a few billion years. The X-ray data was gathered by NASA's Chandra X-ray Observatory. The optical image was provided by the Palomar Observatory and the Digitized Sky Survey.
-- Robert Roy Britt
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