No beginning in sight for star formation.

It kept going and going and going....

As far back in time as astronomers can observe, the cosmos was churning out stars at a prodigious rate, a new study reveals.

Scientists believe that as they peer ever deeper into space and farther back in time, they will eventually come upon the epoch when star formation was not yet in full bloom. However, "we haven't found that place yet," says Charles C. Steidel of the California Institute of Technology in Pasadena. "The universe was remarkably consistent [in making stars] for a fairly large amount of cosmic time."

As far back as 12 billion years ago, when the universe was perhaps 16 percent of its current age, the cosmos was producing stars at a rate about 10 times higher than it does today, Steidel says. The prolific star formation lasted until about 7 billion years ago. Steidel presented his team's findings Jan. 30 at a cosmology workshop in Chicago.

Moreover, an analysis by another team suggests that the cosmos was making stars just as rapidly when it was even younger, about 9 percent of its current age. Piero Madau of the Space Telescope Science Institute (STScI) in Baltimore and his colleagues report their results on the Internet (http://xxx.lanl.gov/abs/ astro-ph/9809058).

The findings contradict a previous report from a team led by Madau and including Steidel. It counted faint, faraway galaxies in the tiny patch of sky called the Hubble Deep Field, which was scrutinized by the Hubble Space Telescope. The team compared this number with a tally of closer galaxies observed by ground-based telescopes. The scientists calculated that star formation reached its zenith when the cosmos was roughly half its current age and was considerably less at earlier times.

Steidel's team has now used ground-based telescopes to search a region 200 times the area of the patch of sky viewed by Hubble. The researchers were surprised to find that star formation remained constant throughout the observable early cosmic history. The findings may only apply to relatively bright galaxies since the telescopes Steidel used could not observe galaxies as faint as those as seen by Hubble.

The researchers now assert that the Hubble Deep Field is simply too small a sample of sky to provide an accurate assessment of star formation. Previous observations by Steidel's team have revealed that massive galaxies in the early universe bunched together tightly (SN: 2/7/98, p. 92). The Hubble field happens to be a region where few galaxies cluster, Steidel suggests.

In a study supporting that assertion, Stefano Casertano and Henry C. Ferguson of STScI and their collaborators counted the number of faraway galaxies in another patch of sky viewed by Hubble. They reported last month in Austin, Texas, at a meeting of the American Astronomical Society that they had found a star-formation rate comparable to Steidel's and about double that found in the original Hubble Deep Field.