Australian National University astronomer Brian Schmidt has been named a joint winner of the 2011 Nobel physics prize for his research into supernovae.

The prize was awarded "for the discovery of the accelerating expansion of the universe through observations of distant supernovae", the Nobel Committee for Physics at the Royal Swedish Academy of Sciences said.

Sorry, this audio has expired Professor Brian Schmidt talks to AM

Forty-four-year-old Professor Schmidt said winning the prize "sort of feels like when my children were born".

"I'm kind of weak in the knees and ... almost speechless at this point," he told AM.

"It's pretty unexpected and so very big news and I guess I'm still just trying to get my head around it.

"I had no inclination. I was actually in Stockholm back in August and have several friends who are members of the Swedish Academy and had no inkling whatsoever."

Half of the 10 million Swedish krona ($1.5 million) prize money went to US citizen Saul Perlmutter, and the other half to Professor Schmidt and US scientist Adam Riess.

"They have studied several dozen exploding stars, called supernovae, and discovered that the universe is expanding at an ever-accelerating rate," the Nobel committee said.

"The discovery came as a complete surprise, even to the laureates themselves."

Professor Schmidt said at first, the discovery seemed too crazy to be true.

"We ended up telling the world we have this crazy result, the universe is speeding up," Professor Schmidt said.

"It seemed too crazy to be right and I think we were a little scared."

'Thank you Australia'

Sorry, this video has expired Australian shares physics Nobel Prize

Professor Schmidt, a joint US-Australian citizen, said he may not have become a Nobel winner if he had not met his Australian wife at Harvard and come to live in the country 17 years ago.

"For me, I think being in Australia was probably, you know, absolutely essential for being part of this," he said.

"I came here at the age of 27 and was able, and was backed with the resources and just the status, to run an international team.

"And you know that's a uniquely Australian thing. So I guess for me I think if I had stayed in the US this might not have happened.

"So I guess I am very grateful to ANU and Australia in general for all the support I got here as a very young person."

Professor Schmidt said one of the reasons he was so readily willing to come to Australia was the opportunity to work at Mount Stromlo, which he described as "one of the great astronomical institutions in the world".

A father of two teenage sons, Professor Schmidt said when he was officially informed that he had won the prize, "The Nobel Prize guy said 'It was nice to have someone young'."

Asked whether he was young enough to win it again, Professor Schmidt said: "I think once in a lifetime is enough."

Infinite mysteries

ANU vice-chancellor, Professor Ian Young, says the Nobel Prize winning work has helped to unveil a universe that, to a large extent, was unknown to science.

"He has shown that what we see in the skies is but a tiny fraction of what is really out there. Brian reminds us of the infinite mysteries yet to be understood," he said.

The breakthrough came in 1998, when one research team headed by Professor Perlmutter and another led by Professor Schmidt and accompanied by Professor Riess reached the same astounding conclusion that the expansion of the universe was rapidly accelerating.

"If the expansion continues to speed up, the universe will end in ice," the Nobel jury said.

The jury added that their discovery had changed mankind's understanding of the universe.

Scientists have known since the 1920s that the universe is expanding, as a result of the Big Bang some 14 billion years ago.

But the discovery that this process is accelerating - and not slowing as many thought - rocked the research community.

The acceleration is thought to be driven by dark energy, although cosmologists have little idea what that is.

They estimate that dark energy - a kind of inverse gravity, repelling matter that comes close to it - accounts for around three-quarters of the universe.

By looking at a certain type of supernova, the astronomers discovered a benchmark for the movement of light.

Their work confirms a theory first proposed by Albert Einstein, which he dubbed the cosmological constant.

The trio will receive their prize at a formal ceremony in Stockholm on December 10, the anniversary of prize founder Alfred Nobel's death in 1896.

ABC/AFP/Reuters