US researchers say they have spotted evidence that a split-second after the Big Bang, the newly formed universe ballooned out at a pace so astonishing that it left behind ripples in the fabric of the cosmos.

If confirmed, experts said, the discovery would be a major advance in the understanding of the early universe. Although many scientists already believed that an initial, extremely rapid growth spurt happened, they have long sought the evidence cited in the new study.

Researchers reported Monday that they found it by peering into the faint light that remains from the Big Bang of nearly 14 billion years ago.

The discovery "gives us a window on the universe at the very beginning," when it was far less than one-trillionth of a second old, said theoretical physicist Lawrence Krauss of Arizona State University, who was not involved in the work.

"It's just amazing," he said. "You can see back to the beginning of time."

Right after the Big Bang, the universe was a hot soup of particles. It took about 380,000 years to cool enough for the particles to form atoms, then stars and galaxies. Billions of years later, planets formed from gas and dust that were orbiting stars. The universe has continued to spread out since then.

Krauss said he thinks the new results could rank among the greatest discoveries in astrophysics over the last 25 years, such as the Nobel prize-winning discovery that the universe's expansion is accelerating.

The results were announced by a collaboration that included researchers from the Harvard-Smithsonian Center for Astrophysics, the University of Minnesota, Stanford University, the California Institute of Technology and NASA's Jet Propulsion Laboratory. The team plans to submit its results to a scientific journal this week, said its leader, John Kovac of Harvard.

To conduct their research, astronomers scanned about 2 percent of the sky for three years with a telescope at the South Pole, where the air is exceptionally dry.

They were looking for a specific pattern in light waves within the faint microwave glow left over from the Big Bang.

The pattern has long been considered evidence of rapid growth, known as inflation.