Three American physicists walked away with the Nobel Prize in physics on Tuesday for discovering that our universe's expansion is accelerating.

Saul Perlmutter, 52, of UC Berkeley and Lawrence Berkeley National Laboratory; Brian Schmidt, 44, of Australian National University in Weston Creek, Australia; and Adam Riess, 41, of Johns Hopkins University and the Space Telescope Science Institute in Baltimore are sharing the prize this year for finding that the universe is moving faster and faster outward.

Half of the $1.5-million that's awarded will go to Perlmutter and the other half will be shared by Riess and Schmidt.

It feels like when my children were born, Schmidt told the BBC about the win. I feel weak at the knees, very excited and somewhat amazed by the situation. It's been a pretty exciting last half hour.

Scientists believe this movement is a result of the mysterious dark energy that fills about 70 percent of the universe. The trio studied Type 1a supernovae and found that distant objects appear to move faster.

Perlmutter, 52, is the leader of the Supernova Cosmology Project, which in 1998 found that galaxies are now retreating from one another faster than they were billions of years ago.

Riess and Schmidt were a part of a different team taking measurements of supernovae billions of light years away from the Earth in order to measure the acceleration of the universe. Perlmutter's team was working on the same problem. The two teams had to locate the most distant supernovae in order to gather information on the expansion of the universe and possibly its future.

What will be the final destiny of the universe? the Royal Swedish Academy of Sciences said in announcing the prize winners. Probably it will end in ice, if we are to believe this year's Nobel laureates in physics. They have studied several dozen exploding stars, called supernovae, and discovered that the universe is expanding at an ever-accelerating rate. The discovery came as a complete surprise even to the laureates themselves.

Riess told Adam Smith, editorial director of Nobel Media, in an interview that the competition lent a sense of urgency to the work.

Riess said when he found out that Perlmutter and his team was seeing similar results as his team were finding they he knew they were on to something.

It went from 'Oh, this is a terrible mistake' to 'Oh, my God, this might be the right answer!' Riess told Smith.  So, it was very exciting.

Nobel Prizes has been handed out since 1901. The will of wealthy a Swedish scientist Alfred Nobel, who invented dynamite, established the award for pioneering achievements in medicine, physics, chemistry, literature and peace.