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Astronomers find 'red nugget' seeds that helped form galaxies

'Red nuggets' are compact galaxies packed with stars. They could represent the initial building blocks for some of the enormous elliptical galaxies astronomers see throughout the universe.

The spiral galaxy IC 2560 in the constellation of Antlia, more than 110 million light-years away from Earth, is shown here in an image from the NASA/ESA Hubble Space Telescope.

Hubble/European Space Agency/NASA/REUTERS

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Mining the archives of two major observatories, a team of astronomers has uncovered what could be a mother lode of "red nuggets" – a type of galaxy that could represent the initial building blocks for some of the enormous elliptical galaxies astronomers see throughout the universe.

Such ellipticals represent the final stages of galaxy evolution, where the vast collection of stars they contain are old and few if any new stars are forming. Some are thought to form through the mergers of large spiral galaxies such as the Milky Way.

But since the initial discovery of red nuggets, astronomers suggest that giant ellipticals also may form with red nuggets as the seeds that over time also grow through mergers with other galaxies.

Despite their small size, it's hard not to see why red nuggets can be so attractive, gravitationally speaking.

Red nuggets are compact galaxies. They can be as small as 10 percent of the Milky Way's size. But their small size belies the large number of stars they contain. The mass of all the stars a red nugget contains can run to more than 10 times the mass of all the stars in the Milky Way.

More important, current models of galaxy formation and evolution can't account for their existence, especially in the early universe, researchers say.

The team, led by Ivana Damjanov with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., has uncovered nine of these nuggets at distances of between 2 billion and 6 billion light-years from Earth.

Although observations of the distant universe with the Hubble Space Telescope had yielded hints that red nuggets were out there, they were hard to distinguish from older, redder stars. Their existence as galaxies was confirmed in 2005 by a team led by French astrophysicist Emanuelle Daddi.

After that, there was an avalanche of observations "finding them at all kinds of high red shifts," Dr. Damjanov says, referring to units of measure that can be converted to distance. In essence, the most distant of these objects were more than 10 billion light-years away, corresponding to a time when the universe was less than 4 billion years old.


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