Using data from NASA's Chandra X-ray Observatory and other optical telescopes, astronomers have developed a powerful new method for investigating dark energy - the mysterious energy that is currently driving the accelerating expansion of the universe.
The technique takes advantage of the observation that the outer reaches of galaxy clusters, the largest structures in the universe held together by gravity, show similarity in their X-ray emission profiles and sizes.
More massive clusters are simply scaled up versions of less massive ones.
"In this sense, galaxy clusters are like 'Russian dolls', with smaller ones having a similar shape to the larger ones," said Andrea Morandi from University of Alabama in Huntsville.
"Knowing this lets us compare them and accurately determine their distances across billions of light years," he added.
By using these galaxy clusters as distance markers, astronomers can measure how quickly the universe was expanding at different times since the Big Bang.
According to Einstein's theory of general relativity, the rate of expansion is determined by the properties of dark energy plus the amount of matter in the Universe, where the latter is mostly made up of unseen material called dark matter.
The latest results confirm earlier studies that the properties of dark energy have not changed over billions of years.
They also support the idea that dark energy is best explained by the "cosmological constant," which Einstein first proposed and is equivalent to the energy of empty space.
"Although we've looked hard at other explanations, it still appears that dark energy behaves just like Einstein's cosmological constant," added study co-author Ming Sun.
To reach this conclusion, the researchers studied 320 galaxy clusters with distances from Earth that ranged from about 760 million light years to about 8.7 billion light years.
"We think this new technique has the ability to provide a big leap forward in our understanding of dark energy," the authors noted in a paper appeared in the Monthly Notices of the Royal Astronomical Society journal.
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