Thu, Dec 18, 2008 - Page 7 News List

While the universe expands, growth of objects gets stunted


The same mystery force that is speeding up the expansion of the universe is also stunting the growth of the objects inside it, astronomers said on Tuesday.

After bulking up rapidly in the first 10 billion years of cosmic time, clusters of galaxies, the cloudlike swarms that are the largest conglomerations of matter in the universe, have grown anemically or not at all during the last 5 billion years, like sullen teenagers who suddenly refuse to eat.

“This result could be explained as arrested development of the universe,” said Alexey Vikhlinin of the Harvard-Smithsonian Center for Astrophysics, who led a multinational team using NASA’s Chandra X-ray Observatory to weigh galaxy clusters from far across space. The group reported the results in a telephone news conference on Tuesday and in two papers that will appear in The Astrophysical Journal.

This stifling of growth, Vikhlinin said, is the “unmistakable signature” of an anti-gravitational force that astronomers have labeled dark energy. It was discovered 10 years ago by astronomers who were using exploding stars called supernovas as distance markers to chart the expansion of the universe. They found that instead of slowing down because of cosmic gravity, as common sense would suggest, the expansion of the universe was actually speeding up, with galaxies zooming apart faster and faster.

Vikhlinin’s results dovetail eerily with the supernova results. Clusters grow by gravity, according to cosmological theory, starting as small dimples in the heat and fizz of the Big Bang and then drawing in surrounding material over the eons. Dark energy would work against gravity and try to push the matter falling in back out, stalling growth.

Together with earlier observations, Vikhlinin said, the new data strengthen the suspicion — but do not prove — that dark energy is a weird anti-gravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a “blunder” almost a century ago. If that is true, the universe is fated to empty itself out eventually, and all but the Milky Way’s closest neighbors will eventually be out of sight.

Other astronomers hailed the work as a new avenue in the investigation of what is happening and will happen to the cosmos.

“To date, only one technique — supernova — has detected dark energy without folding in other observations,” said Michael Turner of the University of Chicago.

The fact that two methods have given similar results for dark energy is a triumph of Einstein’s general theory of relativity, the last word on gravity for the last century, astronomers said.

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