Image: three galaxies
NASA/ESA/Caryl Gronwall, Penn State
Three tiny galaxies about 12 billion light-years from Earth, as imaged by the Hubble Space Telescope's Advanced Camera for Surveys. Astronomers think several such galaxies bunched together to form the Milky Way billions of years ago.
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updated 1/8/2008 3:44:18 PM ET 2008-01-08T20:44:18

Astronomers have spotted small galaxies near the beginning of time that resemble ancestors of our own galactic home.

The tiny galaxies are about one-tenth to one-twentieth the size of the Milky Way and have 40 times fewer stars. Light from the ancient clusters was emitted about 2 billion years after the Big Bang, the theoretical beginning to the universe that occurred about 13.7 billion years ago. So the galaxies are seen as they existed in a very young universe.

The galaxies are not the most distant seen by the Hubble Space Telescope, but astronomers consider them to be the best evidence of precursors to larger, spiral structures such as the Milky Way.

"Finding these objects and discovering that they are a step in the evolution of our galaxy is akin to finding a key fossil in the path of human evolution," said Eric Gawiser, an astronomer at the Rutgers School of Arts and Sciences.

Gawiser and Caryl Gronwall, an astrophysicist at Pennsylvania State University, detailed their findings today at the American Astronomical Society (AAS) annual meeting in Austin, Texas.

"They come in a variety of shapes — round, oblong and even somewhat linear — and we are starting to make precise measurements of their sizes," Gronwall said of the spiral galaxies, which are made mostly of hot, bright stars that emit a unique "Lyman alpha" signature of ultraviolet light.

Statistical analyses and computer simulations of how galaxies bump into one another led Gronwall and Gawiser to conclude that galaxies with strong Lyman alpha signatures are the ancestors of spiral galaxies.

"We knew by our understanding of cosmological theory that spiral galaxies had to evolve from low-mass galaxies such as these," Gawiser said. "The challenge was to actually find them. We'd seen other early universe galaxies, but they were bigger and destined to evolve into elliptical galaxies, not spirals."

Nigel Sharp, a program officer at the National Science Foundation's Division of Astronomical Sciences who was not involved in the work, said Gronwall and Gawiser used Hubble and other observatories to extract an important finding.

"This team has come the closest yet to finding young galaxies that resemble our own Milky Way in its infancy," Sharp said.

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