Dark energy limits galaxy clusters' size

ByABC News
December 16, 2008, 5:48 PM

— -- Clusters of galaxies, the vast islands of stars filling outer space, are limited in their growth by the mysterious force known as dark energy, NASA scientists said Tuesday.

The Chandra X-ray Observatory spacecraft looked at "super-clusters" of galaxies within 7 billion light-years of Earth. (One light-year is about 5.9 trillion miles.) Its findings indicate that dark energy, the anti-gravity force that permeates the universe, began heavily dampening the growth of galaxy clusters about 5.5 billion years ago and hasn't let up.

"This may well be called 'arrested development' of the universe," says research leader Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass.

The Chandra findings also suggest that our own Milky Way galaxy and its neighbors will enjoy a solitary retirement tens of billions of years from now, torn from view of the cosmos by dark energy.

In 1998, astronomers detected dark energy in the accelerating retreat of the exploding stars called supernovas. Scientists believe that showed dark energy is pulling galaxies away from one another.

The Chandra study, scheduled for publication in The Astrophysical Journal, shows that dark energy limits galaxy super-clusters to about 10 clusters, each one containing thousands of galaxies.

Our own Milky Way and its neighbor, Andromeda, will never merge with other galaxies. "We will never lose Andromeda," says Vikhlinin. "Galaxies farther away will move from our sight."