After a five-year survey of 200,000 galaxies, astronomers believe they've confirmed that dark energy is driving our universe apart at an ever-accelerating rate.
Some scientists had suggested that it's gravity, not dark energy, that's pushing space apart, becoming repulsive rather than attractive at large distances.
But the new data, from NASA's space-based Galaxy Evolution Explorer and the Anglo-Australian Telescope on Siding Spring Mountain in Australia, supports the idea that dark energy works as a constant force, uniformly affecting the universe and propelling its expansion.
"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," says Chris Blake of the Swinburne University of Technology in Melbourne.
"The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time."
Dark energy is thought to make up about 74 percent of the universe. Dark matter accounts for 22 percent, with so-called normal matter only making up about four percent.
"Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the big bang, is speeding up," says Jon Morse, astrophysics division director at NASA headquarters.
"Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy."