Astronomers find new evidence of 'dark energy'

WASHINGTON — Scientists reported Tuesday they had found new evidence of a "dark energy" that is pushing the universe apart — and could someday rip up the galaxies and even the atoms we're all made of.

The new evidence also agrees with previous suggestions that the mysterious repulsive force is causing the expansion of the universe to accelerate, rather than slow down, they said.

"It's as if you threw an apple into the air and, instead of slowing down and falling back, it begins to accelerate upwards," said Andy Fabian, an astrophysicist from Cambridge University in England.

The new evidence of the existence of "dark energy" comes from studies of 26 distant clusters of galaxies by the Chandra X-ray Observatory, Fabian and other scientists said in a briefing at National Aeronautics and Space Administration headquarters.

The studies also allowed astronomers and astrophysicists who study Chandra data to calculate the amount of "dark energy" in the universe.

They concluded that ordinary matter — the stuff we see — accounts for about 4 percent of the universe. Dark matter, a different type of stuff that cannot be perceived directly, even if a light is shined on it, makes up about 21 percent of everything, and dark energy accounts for the remaining 75 percent, scientists said.

The Chandra observations agree with earlier conclusions that beginning about 6 billion years ago, the expansion of the universe began to pick up speed.

That was not what scientists had expected for nearly 70 years.

Rather, after astronomer Edwin Hubble's 1929 discovery that the universe is expanding, they have believed that as momentum from the "Big Bang" decreased under gravity's resistance, the expansion would slow down.

Some believed that it would eventually stop, and the galaxies would fall back to a central point in a "Big Crunch."

Instead, dark energy is apparently causing them to move apart faster and faster, astronomers now say.

The observations agree with the concept of a "cosmological constant," first proposed by Albert Einstein — who later discarded it — as a force that countered the attractive force of gravity.

However, if the "dark energy" force is not constant but is actually growing stronger, then in 30 billion years or so it could cause everything in the universe to come apart in what cosmologists have started to call "the Big Rip."