Faint "Teenage" Galaxies Found in Early Universe

Richard A. Lovett
for National Geographic News

November 29, 2007

"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.

Accidental Find

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.

Ultraviolet light excites hydrogen atoms in the gas clouds, causing them to emit a characteristic wavelength of red light called the Lyman alpha wavelength, which Rauch compared to "a flagpole that sticks out from the spectrum."

The research involved repeatedly aiming the 26-foot (8-meter) Very Large Telescope in Chile at the same tiny patch of sky for the equivalent of nearly two weeks' worth of night observing—about 92 total hours of observation.

But instead of gas clouds, the researchers ended up detecting 27 faint galaxies, all shining at the same wavelength because of ultraviolet light emitted during the process of star formation.

"Whenever the conditions were right, the on-site astronomers in Chile would take data for us, over a three-year period," Rauch said. "It's probably the deepest [longest-duration] spectra in the history of astronomy."

The research will be published in the March issue of the Astrophysical Journal.

Boots on the Ground

According to the Carnegie Institution, the new objects are ten times fainter than any galaxies before seen from the ground.

That's a triumph for ground-based astronomy, which has been surpassed in many people's eyes by orbiting observatories such as NASA's Hubble Space Telescope.

Hubble and its kin can't make extended spectroscopic observations of the same small area. (Read more on the debate between ground- and space-based telescopes).

The next generation of terrestrial telescopes are expected to keep pace with the newest orbiting telescopes, raising hopes for further discoveries.

"They're highly complementary approaches," Rauch said.

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