Scientists find more evidence for dark energy

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 five 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, Dr. Vikhlinin said, is the “unmistakable signature” of an antigravitational 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.