A Galaxy Far, Far, Far Away

Redder is better, as far as astrophysicists interested in the early evolution of the universe are concerned. The more the light from a celestial object is shifted toward the red end of the spectrum, the farther and older it is. Now astronomers claim to have found the most redshifted galaxy yet: It's more than 13 billion years old and hails from an era when the earliest galaxies were forming. The new discovery helps scientists figure out exactly how and when galaxies first came to be.

About 400,000 years after the big bang, the universe was a hot cloud of neutral hydrogen gas. One billion years later, that gas had burned away, ionized by bright light from stars and galaxies. Somewhere in between, those stars had to ignite and the galaxies had to coalesce. Although scientists have theories about how and when this happened, they had few hard data. That all changed in the past few years thanks, in part, to a phenomenon known as gravitational lensing. The immense mass of clusters of galaxies acts like a telescope, bending and focusing light, allowing scientists to spot much more distant objects.

Such a lens helped a team of astronomers find the most ancient galaxy yet. Using the Very Large Telescope in Chile, they scanned the region of a well-known cluster of galaxies, Abell 1835, as they report in an upcoming issue of Astronomy & Astrophysics. Its lensing effect revealed faint and distant galaxies. Among the venerable crowd, one seems to have a "redshift" of 10--a measure of how fast the galaxy is moving and how far away it is--beating the previous record holder, at a redshift of 7. According to team member Daniel Schaerer, an astronomer at the Observatory of Geneva, the image shows an extremely small galaxy when the universe was a mere 460 million years old. "It's quite typical of the properties you would expect a galaxy to have at this redshift.” At that time, he says, most theorists envision small galaxies forming that will eventually merge to form bigger ones.

Although California Institute of Technology astronomer Richard Ellis is skeptical as to whether this galaxy is truly as far away as claimed, he says that there's no doubt that a current spate of high-redshift galaxies are shedding important light on the nature of the early universe. "They're giving us new information on how the earliest objects in the universe formed," he says. "The overall idea is that these objects began to evolve, building up from small to big, and this is borne out by these observations."

Related sites
Background information about the evolution of the universe
The Very Large Telescope

Posted in Space