BRIDGEPORT, WV (S-M) - NASA's Galaxy Evolution Explorer has imaged galaxies which appear to be in a middle stage of evolution between young spiral galaxies and older elliptical galaxies.


"Whether one kind of galaxy can develop into another has long been an important question," said Senior Editor Glen Ward. "What these new images show are galaxies which are in between the young, blue spiral galaxies and older, more reddish ellipticals. These images show that spirals do develop into ellipticals, often through collisions with other galaxies. This strongly supports the view that galaxy development follows a predictable path which begins with hot young blue stars in a spiral and ends with old red stars in an eliptical configuration."


"Our data confirm that all galaxies begin life forming stars," said Chris Martin, the principal investigator for the Galaxy Evolution Explorer. "Then through a combination of mergers, fuel exhaustion and perhaps suppression by black holes, the galaxies eventually stop producing stars."


Scientists are still researching precisely what causes galaxies to age and turn red. "Somehow, the galaxies seem to run out of star-forming materials," said Ward. "Then after a few billion years, the stars in the galaxies age and we see them as older red galaxies."


Since scientists don't have billions of years to watch individual galaxies, they had to scan thousands of galaxies to observe them at various stages of evolution. "The nurture theory of galaxy evolution predicted that there would be galaxies in transition," said Martin. "Finding these galaxies required ultraviolet light, because they really stand out at this wavelength. And because they are rare, we had to look at many. The Galaxy Evolution Explorer allowed us to do this."

Copyright 2007 Starry Mirror and Glen Ward

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NGC1291, a so-called teenage galaxy.  (NASA)