Dust glow hints at wave of early star birth.

For every star that glitters, many more lie behind a veil of dust.

Observing the universe at submillimeter wavelengths, where the glow from star-warmed dust is brightest, astronomers have found evidence that at early times in the universe, stars were born at a rate five times higher than visible-light studies have indicated. The images hint that the vast majority of stars in the cosmos were born well before the cosmos had reached half its current age.

"To some astronomers, it's a nightmare; to others, it's just what they expected," says James Dunlop of the University of Edinburgh in Scotland, a member of one of the two teams reporting their work in the July 16 NATURE. A rapid, early burst of star formation "could put a tight constraint on theories of galaxy formation," says Douglas Scott of the University of British Columbia in Vancouver in an accompanying commentary.

Early birth of stars and galaxies is consistent with certain theories of galaxy formation, says cosmologist Jeremiah P. Ostriker of Princeton University. These models assume that most of the matter in the cosmos is composed of invisible, slow-moving material known as cold dark matter and that this material has too low a density to keep the cosmos from expanding forever.

The two teams used a new high-resolution camera on the James Clerk Maxwell Telescope atop Hawaii's Mauna Kea. Amy J. Barger of the University of Hawaii in Honolulu and her colleagues pointed the telescope at two small, seemingly blank regions of the sky, while Dunlop and his collaborators examined the Hubble Deep Field, a patch of sky that has been studied extensively in visible light.

A submillimeter telescope is well suited for detecting dust in distant galaxies. The dust tends to quench visible and ultraviolet light emitted by stars and reradiate it in the far infrared. The expansion of the universe shifts the far-infrared radiation from distant galaxies to longer, submillimeter wavelengths.

Maps of the far-infrared background glow had already demonstrated that visible-light images drastically underestimate the amount of star formation (SN: 1/10/98, p. 20). The new observations reveal the dust in individual galaxies that creates some of the glow.

The researchers strongly suspect, based on the emissions recorded at two submillimeter wavelengths, that at least four of the seven galaxies they collectively identified are extremely distant, hailing from a time when the universe was no older than one-third its current age. Mark Dickinson of the Space Telescope Science Institute and the Johns Hopkins University, both in Baltimore, notes that to establish that the cosmos formed most of its stars when it was just a few billion years old, astronomers must directly measure how far away the galaxies reside.