Chandra unlocking mystery of 'dark energy'
X-ray measurements indicate universe could expand forever
(CNN) -- The Chandra Space Telescope has gathered further evidence the universe is expanding at an accelerating rate, scientists at NASA and Britain's Institute of Astronomy announced Tuesday. The finding sheds new light on a force known as "dark energy."
"Dark energy is perhaps the biggest mystery in physics," said Steve Allen at the Institute of Astronomy in Cambridge, England.
According to scientists, dark energy is the force that fills the space between galaxies and drives them apart.
"The universe really is accelerating," Allen said. "By using Chandra to study galaxy clusters, we have obtained strong new evidence for dark energy and clear and direct confirmation that the expansion of our universe is accelerating."
The Chandra telescope took X-ray measurements from 26 clusters of galaxies ranging from 1 billion to 8 billion light years from Earth. Chandra's probe of dark energy relies on the X-ray observations to study the hot gas in galaxy clusters.
By using Chandra's data to figure out the ratio of hot gas to dark matter, astronomers determined how far away the clusters were and at what point in time they were viewing them, NASA's Web site says.
They concluded the clusters were farther away than expected, indicating an accelerated state of expansion.
According to scientists, these recent discoveries offer further evidence that the universe turned from decelerating expansion to accelerating 6 billion years ago when the mysterious force of dark energy took over and out-powered gravity, the force slowing the universe expansion down.
Scientists place the cosmos at 12 billion to 15 billion years old.
Based on the Chandra data, scientists believe the density of dark energy appears to be fairly constant, or at least increasing at a rate where the universe will continue to expand forever.
In 1929, Edwin Hubble first suggested that the universe was expanding. But Hubble and conventional astronomy for the next 70 years said the expansion was decelerating because of the force of gravity.
In 2001, based on a Hubble Space Telescope observation of a supernova, or exploding star, 10 billion light years away, NASA scientists believed they had evidence to support the theory that the universe is expanding at an accelerating rate. But NASA needed more evidence to back up the findings.
The Chandra Space Telescope orbits the Earth every 64 hours at altitudes ranging from approximately 10,000 miles to 82,000 miles, about one-third the distance to the moon.
It was launched in 1999 and is one of the "great observatories," along with space telescopes Hubble, Spitzer and Compton (de-orbited in 2000).
CNN's Dave Santucci contributed to this report.