for National Geographic News
"Teenage" galaxies—believed to be the building blocks for larger galaxies such as our own Milky Way—have been found for the first time, scientists say.
Researchers discovered more than two dozen of the distant, faint objects—known as protogalaxies—while using one of the world's largest telescopes to peer backward to when the universe was only two billion years.
(Related: "'Rogue' Dwarf Shines New Light on Tiny Galaxies" [November 21, 2007].)
"We think these are the building blocks of typical galaxies," said Michael Rauch, an astronomer at the Observatories of the Carnegie Institution of Washington who was part of the discovery team.
"Small galaxies merge with each other to form bigger galaxies, and these merge to form things like our Milky Way, which is a relatively big galaxy," he said.
Fellow team member George Becker, also from the Carnegie observatories, added: "If you call them 'teenage,' that implies they grow into other things, which is probably true."
Scientists have long suspected that such galaxies existed, but until now they had never been observed.
The light from protogalaxies has been traveling for 85 percent of the universe's roughly 13-billion-year existence, meaning they are extremely faint and far away, experts point out.
The international team of scientists didn't start out looking for galaxies.
Instead they were searching for giant gas clouds believed to have existed early in the universe's development.
Specifically, the researchers were looking for clouds illuminated by ultraviolet light from bright, distant galactic cores known as quasars.
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