Star birth, which transformed primordial gas into the countless starry galaxies of the present day universe, surged to high levels much earlier than astronomers had thought. Two teams of observers have looked into the early universe for the long-wavelength radiation that signals star formation in dusty young galaxies. In tomorrow's Nature, they report seeing galaxies rapidly spawning stars when the universe was less than a third of its present age.
Astronomers have been searching at great distances--which correspond to earlier times--to find the heyday of star birth. But interstellar dust is thick in star-forming regions, hiding the light of hot young stars and reradiating it in the infrared. Observations by infrared satellites have already revealed large numbers of star-forming galaxies as much as halfway back to the big bang. But for even older, more distant stars and galaxies, the expansion of the universe stretches the infrared radiation into the submillimeter waveband, a twilight region of the spectrum between infrared and radio.
Earlier this year, a U.K. team led by Michael Rowan-Robinson of London's Imperial College pointed a submillimeter telescope on Mauna Kea, Hawaii, at the Hubble Deep Field, the small patch of sky where the Hubble Space Telescope captured optical images of some of the most distant galaxies ever. Five of the brightest submillimeter sources they found match up with faint, old galaxies in the Hubble image, and four of the five date from when the universe was between a third and a fifth of its present age--up to 9 billion years ago. Their submillimeter brilliance indicates that these galaxies are spawning stars perhaps 100 times faster than our own galaxy, says team member James Dunlop of the University of Edinburgh. A U.S.-Japanese group has made other submillimeter images that support this picture of frenzied star birth in the early universe.
The observations are "a very exciting new development," says Max Pettini, an astrophysicist at Britain's Royal Greenwich Observatory. Star formation, he says, is "part and parcel of the broader question of how the universe evolved from the smooth conditions of the big bang into the galaxies we see today." However, Charles Steidel of the California Institute of Technology cautions that the distance and hence the age of these submillimeter sources is "somewhat ambiguous," because of the submillimeter camera's coarse resolution.