Astronomers wielding the Hubble Space Telescope say they've pushed back the curtain a bit on a mystery so bizarre it caused even Albert Einstein to doubt himself.
Using Hubble to examine the light from 24 exploding stars as far as 9 billion light-years away, astrophysicists in Baltimore concluded that "dark energy," the unexplained force that accelerates the expansion of the universe, has been around - apparently unchanged - for at least 9 billion years.
Nobody knows what dark energy is or how it works. Some have dubbed it "a black cat in a coal bin." But it's a huge part of the universe around us, representing perhaps 70 percent of all the matter and energy in existence.
Scientists say the new data from Hubble should help theorists discard several competing theories, some of which had suggested a more rapidly changing nature for dark energy or a flawed understanding of gravity.
"This is a significant clue in the quest to understand what is probably one of the most pressing questions in physics," said Adam Riess, an astrophysicist at the Space Telescope Science Institute and the Johns Hopkins University, who was principal investigator in the study.
His work also helps to confirm a troublesome bit of Einstein's 1915 general theory of relativity and its conclusions about the nature of gravity.
"What we've learned is that Einstein was very smart, and his theory of gravity was really good," said Sean Carroll, a senior research associate at the California Institute of Technology who was not connected to the Hubble research.
Riess' findings are scheduled for publication in February in the Astrophysical Journal.
In 1998, Riess was the first to report the existence of "dark energy," so called because it appears to work even in the emptiest vacuum of space. He used Hubble to examine the light from a class of distant exploding stars called Type 1a supernovas - chosen because they're bright enough to see across the vast distances that astronomers needed to penetrate. Only Hubble can see them so far away.
Scientists also like Type 1a supernovas because their chemistry and physics are well understood - and they're known to have a consistent brightness. That allows astronomers to compute and compare their distance in space (and in time, because light from more distant objects takes longer to reach us). It's like judging the distance of fireflies across a field by how bright they appear.
