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HubbleSite Hubble Helps Solve Mystery of Ultra-Compact, Burned-Out Galaxies


Space Telescope Science

A certain class of massive galaxies in the early universe lived fast and died young. By "died" astronomers mean that the galaxies had completed building stars just 3 billion years after the big bang. By contrast, our 12-billion-year-old Milky Way galaxy continues making stars today. When star formation stops, the aging stellar population looks redder in the star-forming galaxies that are more bluish. The nickname for the essentially "burned-out" galaxies is "red and dead."

By combining the power of Hubble with infrared space-based telescopes and ground-based telescopes, astronomers have now solved a decade-long mystery as to how compact elliptical-shaped galaxies existed when the universe was so young. These "red and dead" galaxies have now been linked directly to an earlier population of dusty starburst galaxies. These objects voraciously used up available gas for star formation very quickly. Then they grew slowly through merging as the star formation in them was quenched, and they eventually became giant elliptical galaxies.

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