The universe expanded rapidly an instant after the Big Bang, physicists studying data from a NASA space probe say.

NASA's Wilkinson Microwave Anisotropy Probe or WMAP spacecraft is looking at the afterglow of energy from the Big Bang, believed to have occurred about 13.7 billion years ago, to help researchers understand how the universe formed.

"We report today the most precise measurements of our infant universe," said Charles Bennett, principal investigator for the NASA mission.

The infant universe with warm spots in red and cooler spots in blue. The white bars show direction of the oldest light. (Courtesy: NASA)

"We have new evidence that the universe suddenly grew from sub-microscopic to astronomical size in less than the blink of an eye," Bennett told a telephone news conference.

The event happened in less than a trillionth of a second, according to the researchers, who analyzed variations in the brightness of microwave radiation, or cosmic microwave background, to find the evidence.

The findings also help explain how planets and stars eventually formed.

In 2003, researchers used WMAP to unveil the universe's baby photo, which pinned down the age of the universe.

The latest data confirms the age, but changes estimates of when stars first formed to 400 million years after the Big Bang.

WMAP's mission is scheduled to continue through September 2009.