The COBE universe: portrait at 300,000.

The COBE universe: Portrait at 300,000

Now there's not place left for anomalies to hide. After operating for five months, two instruments aboard the Cosmic Background Explorer (COBE) spacecraft have completed maps showing the distribution of microwave and infrared radiation across the whole sky. Like the preliminary results reported last January (SN: 1/20/90, p.36), the latest measurements of the radiation left over from the Big Bang reveal no distortions that suggest the universe had anything other than a remarkably uniform, smooth beginning.

"We've looked everywhere, and the sky is very smooth," says Charles L. Bennett of the NASA Goddard Space Flight Center in Greenbelt, Md. "This is what the universe looked like only 300,000 years after the Big Bang." Bennett and other members of the COBE team reported their findings at this week's American Physical Society meeting in Washington, D.C.

The mot prominent features visible in the new sky maps are two broad regions or loes -- one slightly warmer than the average sky temperature and the other slightly cooler -- at diametrically opposite corners of each map. New analyses of COBE data clearly demonstrate that these features result from Doppler shifts in wavelength caused by the motion of the solar system relative to the microwave background.

That result goes a long way toward settling a long-standing question as to whether this so-called dipole effect represents the remnant of some kind of structure or density fluctuation present in the early universe, or is simply the result of solar-system and galactic motion. "We've never really understood whether or no that dipole we see in the sky is due to our velocity . . . or is intrinsic in the background radiation," says David T. Wilkinson of Princeton (N.J.) University. "This shows it's no intrinsic. That's an important result."

The finding also provides additional confirmation that the solar system, the Milky Way and its galactic neighbors are all moving at a significant velocity toward an apparent concentration of mass -- a velocity above and beyond that resulting from the expansion of the universe.

Subtracting from the sky map the observed dipole effect and the band of microwave emission from the Milky Way leaves a startling uniformity. "We see nothing," Bennett says. "That suggests, in some sense, a very simple cosmology." Whatever turbulence occurred in the universe's early days after the Big Bang must have been minimal.

The team is now trying to identify possible sources of error in the measurements. "We have a big job ahead of us in that we're looking for deviations from a very simple picture," says Goddard's Michael G. Hauser. "We have to understand our instruements very well. We have to understand aht the sky is doing, and that job is still largely before us."

COBE itself continues to collect data. "It's an astonishingly successful instrument," Wilkinson says. "Very little has gone wrong." The only major problem surfaced when one of the spacecraft's gyroscopes failed early in the mission.