A Long, Hard Look at the Early Universe

By Phil Berardelli
ScienceNOW Daily News
28 November 2007

Astronomers have finally spotted the small and young galaxies that represent the building blocks of full-sized galaxies such as the Milky Way. The findings represent the first examples of what could become a plentiful source of astronomical data about the formation of the universe.

Galaxies don't spring into existence full-sized overnight. In an early era of the universe, tiny versions of the Milky Way coalesced out of gigantic clouds of hydrogen gas that permeated the cosmos. Over the course of a billion or so years, these budding galaxies began merging, with half a dozen or more of them needed to form galaxies the size of our own. At least, that's what the theorists calculated. The problem is that, because they are so faint, such small galaxies have been extremely difficult to detect. The search has been "a hard game," says astronomer J. Christopher Mihos of Case Western Reserve University in Cleveland, Ohio.

What was needed, it turns out, was patience and a great set of instruments. Astronomers from the University of Cambridge in the U.K. and from the Observatories of the Carnegie Institution of Washington in Pasadena, California, focused two of the world's biggest telescopes on the same tiny patch of sky, near the constellation Aquarius, for a total of 92 hours--practically an eternity of observational time. Voil%26agrave;! By capturing spectra of hydrogen gas clouds, backlit by stars within the galaxies and 10 times fainter than anything seen before, the researchers identified 27 protogalaxies from a time when the universe was only 2 billion years old--and at a distance from Earth of 22 billion light-years. As the team will report in the 1 March 2008 issue of The Astrophysical Journal, the chemical signature of the objects' dim light confirms their existence and very young age.

Now that they know that they can find such objects, co-author and Carnegie astronomer Michael Rauch says he and his colleagues will try to learn more about protogalaxies by observing other swaths of the sky. "The beauty is that these new galaxies are so numerous that you can stare anywhere in the sky and find some of these objects, even in a very small field," he says. Before this study, astronomers had assumed that they could detect only the brightest distant galaxies from ground-based telescopes, Rauch notes. That was "the tip of the iceberg," he says. "Now we have dived deep enough to see the bulk of the iceberg itself."

Astronomer Mark Voit of Michigan State University in East Lansing agrees. "People have been searching for objects like these for a long time without success," he says. "It really does open a new window on the process of galaxy formation."