By Conor Sharkey

A Strabane man is among four Cambridge University astronomers who have shared the most important award in cosmology for their role in discovering that the universe's expansion is speeding up.

Dr Richard McMahon, Dr Mike Irwin and Dr Nic Walton from the Institute of Astronomy, and Dr Nelson Nunes from the Department of Applied Mathematics and Theoretical Physics, have all been named as winners of the 2007 Gruber Cosmology Prize.

All the Cambridge researchers were in one of the two teams that made the Dark Energy discovery at around the same time in 1998. This mysterious force, which astronomers still do not fully understand, is accelerating the expansion of the universe and accounts for 75 percent of the mass-energy density within it.

A little under a decade ago, the idea that the universe was somehow expanding at an increasing speed was an outlandish notion that academics found it difficult to accept. Existing theories suggested that it would either expand then contract, or expand forever, slowing over the millennia.

Evidence that both of these theories might be flawed was, however, growing at the same time. Two teams, led by Dr Saul Perlmutter and Dr Brian Schmidt, set out to resolve the matter once and for all.

Racing neck and neck, they examined exploding stars which are visible from the earth despite being billions of light years away and billions of years old. This allowed them to measure the speed at which distant objects in space are travelling away from us, as well as how far away they are.

data correct

To their surprise, and independently of one another, each team discovered that the fate of the universe is just to keep expanding, faster and faster. Initially neither group accepted their findings and spent time trying to find out where they had made an error. But the data was correct – it was the accepted model of the universe that was wrong.

"We worked for almost ten years trying to measure how much the universe was slowing down due to gravity," Dr McMahon said. "We were very shocked to find the opposite of what we expected and that the universe was accelerating as it expanded.

"This acceleration of the universe appears to have started around ten billion years ago and is caused by kinetic energy that is released as the universe expands. Ten years on, our results are widely accepted and this energy is called Dark Energy. It makes up 75% of the total mass-energy of the universe but is almost undetectable. The earth contains just one hundredth of a gram of Dark Energy."

The Gruber Cosmology Prize honours a leading cosmologist, astronomer, astrophysicist or scientific philosopher for theoretical, analytical or conceptual discoveries leading to fundamental advances in the field. A previous Cambridge recipient is Professor Martin Rees, who won the prize in 2001 for his work in unravelling the complexities of the universe.

Both teams were presented with the prize at a recent private ceremony in Trinity College at the University of Cambridge. The university's Institute of Astronomy also hosted a public lecture given by the two team leaders, Drs Perlmutter and Schmidt, about how the discovery was made, and what its implications are for the future of the Universe.