Dark energy is stunting the growth of the universe鈥檚 galaxy clusters, new observations reveal.
The finding uses a new technique to confirm that the universe is accelerating in its expansion, pushed apart by a mysterious repulsion 鈥� dark energy 鈥� that is overpowering the effect of gravity.
鈥淲e are in effect looking at dark energy from a new angle that was never quite possible before,鈥� Alexey Vikhlinin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, told reporters on Tuesday.
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Vikhlinin and colleagues used NASA鈥檚 to measure the hot gas in 86 galaxy clusters. These groups of hundreds or thousands of galaxies are filled with 100-million-degree-gas that can best be detected with X-ray telescopes.
The team estimated the total mass of each cluster and their distance from Earth. In the absence of dark energy, gravity鈥檚 pull should have caused the total number of clusters to increase by a factor of 50 over the last 5.5 billion years, Viklinin said.
Instead, something counteracted the force of gravity, and the number of clusters only increased by a factor of 10. 鈥淭his is an unmistakable signature of dark energy,鈥� Vikhlinin said.
Independent methods
Several other research groups are also studying dark energy by observing galaxy clusters, and astronomers expect the precision of the approach to improve with more observations.
The effect of dark energy was first reported in 1998, when two teams of astronomers found exploding stars that were dimmer, and thus farther away, than expected.
Since then, mounting evidence 鈥� from the big bang鈥檚 afterglow and ripples in the distribution of matter in the universe 鈥� have honed a picture of the universe in which some 72% of all matter and energy is composed of dark energy.
鈥淭his is very impressive and important work,鈥� says , who heads NASA鈥檚 Wilkinson Microwave Anisotropy Probe, a satellite that measures the big bang鈥檚 afterglow. 鈥淭he results provide a crucial cross-check against the pre-existing set of cosmological results.鈥�
Theorist David Spergel of Princeton University agrees, saying the fact that different techniques are all consistent is a 鈥渢riumph鈥�.
He says the new study will help pin down dark energy鈥檚 properties, paving the way for researchers to one day determine what it is. The leading idea is that it is an inherent property of space itself 鈥� called the cosmological constant 鈥� but an alternative theory called quintessence posits that it could be an as-yet-unidentified quantum field that can vary depending on time and place.
Journal reference: (forthcoming)
