Astronomers say the Universe is accelerating.  They say the rapid expansion appears to be caused by the mysterious black space surrounding planets and stars.

The observation that the Universe is ever expanding is at odds with the accepted notion that gravity will eventually slow the expansion of the Universe, which was believed to be created by the Big Bang some 13 billion years ago. 

A team of astrophysicists at Harvard University's Smithsonian Astrophysical Observatory in Cambridge, Massachusetts says it has found evidence that energy, generated by mysterious dark matter, is behind the Universe acceleration.

Using the US space agency NASA's Chandra X-ray observatory, Alexey Vikhlinin and colleagues observed 86 tightly-packed galaxy clusters.

Vikhlinin says in time, dark energy will edge out the visible Universe.

"It's not tomorrow but it's roughly double the age of the Universe today, and you will see very strong effects on observable galaxies," he said.
David Spergel is an astrophysicist at Princeton University in New Jersey.

"One way of thinking about this is that even nothing - empty space - weighs something," Spergel explained.  "And because in our Universe we have a lot of nothing, it has a major effect on our evolution and causes space itself to accelerate."

The research provides crucial evidence that dark energy exists. 

Study co-author William Forman says the findings add another dimension to Einstein's Theories of Relativity which underlie scientists' understanding of the Universe.

"Einstein's equations apply over a truly remarkable range of environments, including the universe as a whole, super massive black holes,  the stretching of time required to make our GPS (global positioning satellite) systems work," Forman said. "But despite all these remarkable successes, conceptual changes to Einstein's vision may still be needed."

The study on dark energy are published in the December 16 Astrophysical Journal.