'Dark energy' expands, contracts universe: researchers

Wed Dec 17, 8:34 am ET

WASHINGTON (AFP) – Mysterious "dark energy" works simultaneously to expand the universe and shrink objects inside it, astronomers in the United States said Tuesday.

By studying how gravity competes with the expansion of galaxy clusters, scientists have found "a crucial independent test of dark energy," said the research compiled by scientists using NASA's Chandra X-ray Observatory.

"This result could be described as 'arrested development of the universe,'" said lead researcher Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in the northeastern state of Massachusetts.

"Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down."

Dark energy makes up about 70 percent of the universe, said the research to be published in the February 10 issue of Astrophysical Journal.

After years of research, scientists now believe that dark energy is "a form of repulsive gravity that dominates the universe, although they have no clear picture of what it actually is," the research report said.

"What this means for the future of this universe is that accelerated expansion will proceed forever but will probably not result in a Big Rip," said Vikhlinin.

"That is, nearby galaxies will eventually disappear from our sight, but the structures already formed by clusters of galaxies and our own galaxy will not be torn apart, not in the near future anyway."

The research differed from previous studies on supernovas, which are the explosive deaths of massive stars, and provided the "strongest evidence yet that dark energy is the cosmological constant," he said, similar to the energy of empty space.

"Or in other words, that 'nothing weighs something,'" said Vikhlinin.

The discovery of dark energy in 1998 sparked renewed interest in Albert Einstein's theory of cosmological constants, a modification of his theory of relativity which suggests a possible repulsive force in the universe.

Einstein hypothesized that a repulsive force in space could explain the universe's equilibrium with the force of gravity.

Without such a contrary force, gravity would cause the universe to implode, Einstein suggested.