Keck Finding: Did Stars Predate Galaxies?

Article excerpt

In astronomy, one maxim has always seemed to hold true: Stars reside in galaxies.

But new observations with the world's largest optical telescope suggest that the first generation of stars formed more than a billion years before galaxies.

Antoinette Songaila and her colleagues base this tentative conclusion on a study of heavy elements--atoms heavier than helium--in gas clouds that fill the space between galaxies several billion light-years from Earth. The team, from the University of Hawaii in Honolulu, finds that the clouds aren't pristine reservoirs of hydrogen and helium, the main elements forged in the Big Bang.

Instead, the clouds, observed as they appeared when the cosmos was less than one-third its current age, are contaminated with highly ionized carbon, an element that could only have been created inside stars.

The clouds appear too wispy to be fledgling galaxies. Unlike denser hydrogen clouds, which rank as prime candidates for galaxies in the making, these clouds do not seem to cluster together. In addition, most of the clouds the group studied had roughly the same abundance of carbon, regardless of their inferred density. This argues that the carbon represents a pollutant from some outside source.

These lines of evidence suggest, but do not prove, that the carbon came from a generation of stars that predated the clouds and the formation of galaxies, Songaila says.

"Scientists have long suspected that there might have been an early generation of stars that formed prior to the period of galaxy formation," says Lennox L. Cowie, who collaborated with Songaila. "Our observations could be the first evidence for this population."

Songaila, Cowie, Tae-Sun Kim, and Esther M. Hu report their work in the April Astronomical Journal.

The team used the 10-meter Keck Telescope atop Hawaii's Mauna Kea to measure the abundance of carbon in vast, low-density clouds of hydrogen. Like foreground trees silhouetted by a distant searchlight, these clouds make their presence known by absorbing light from a bright background quasar, forming a thicket of absorption lines known as the Lyman-alpha forest.

The team found that in the clouds, up to one atom in a million was ionized carbon. …