Astronomers use galactic magnifying lens to illuminate dark energy | Science| In-depth reporting on science and technology | DW | 20.08.2010
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Astronomers use galactic magnifying lens to illuminate dark energy

European and American scientists take a step closer to understanding the unknown force by measuring 'gravitational lensing' from a galaxy cluster 2.2 billion light years away.

The Abell 1689 galaxy

The Abell 1689 galaxy cluster, 2.2 billion light years away, with the mass distribution of the dark matter in the gravitational lens overlaid in purple

In a paper published today in the journal Science, European and American scientists report that they have developed a new technique to measure dark energy, a mysterious force that astronomers and astrophysicists have struggled to understand.

Since the 1920s, astronomers have known that the universe is expanding. But in 1998, scientists identified something called "dark energy," a strange force that is accelerating the rate of expansion of the universe itself. However, they have not identified precisely what the nature of this force is.

According to the American space agency NASA, all mass-energy in the entire universe is comprised of 74 percent dark energy.

The new technique involves using "gravitational lensing" to learn about the structure of the universe itself.

Massive objects like the cluster act like lenses, which magnify and distort light from galaxies behind them, which was predicted decades ago by Einstein’s theory of general relativity. This effect is a significantly larger version of what happens when examining a small object with a magnifying glass.

For this study, the scientists used one of the largest known galaxy clusters, Abell 1689. By analyzing the distortion of the distant galaxies' light, astronomers can get a better understanding of the geometry of the universe, and therefore the role of dark energy in it.

Jean-Paul Kneib, an astrophysicist at the University of Provence in southern France and one of the paper's authors, said that this new technique could substantially advance scientists' understanding of dark energy.

"With this new technique, in a few years' time we should be able to say something very accurate about what is dark energy, what is its nature, and what will be eventually the fate of the universe," he said in an interview with Deutsche Welle.

Hubble Space Telescope

The Hubble Space Telescope was used to study galaxy cluster Abell 1689

Mapping light

While the concept for new technique is fairly simple, actually doing it was quite complicated, Kneib said.

The study required powerful telescopes -- including the Hubble Space Telescope -- and massive computers to model the galaxy cluster. The team analysed the distorted images of 34 galaxies behind Abell 1689.

They then combined the key result from their finding - dark energy's "equation-of-state parameter" - with estimates made using other methods.

"With this one result that we get from this one cluster, if we add that into the mix," said Priya Natarajan, a professor of astronomy at Yale University, and a co-author of the paper, in an interview with Deutsche Welle. "We can bring down the current errors by 30 percent, which is hugely significant."

Sherry Suyu, a post-doctoral researcher at the University of Bonn, who was not part of the study, noted that a more precise equation-of-state parameter will help narrow down the possible forms of dark energy.

Despite the fact that the majority of the universe is made up of dark energy, "no one knows what it is," she said in an email.

More clusters

The researchers are eager to apply their method to more galaxy clusters.

That should lead to more convincing results, added Douglas Clowe, a professor of astrophysics at Ohio University in the United States, who also was not part of the study team.

He points to proposed astronomical surveys, such as the ground-based Large Synoptic Survey Telescope and satellite-based Euclid mission that could help confirm the results of this new study.

"[This will] greatly expand the number of clusters available for analysis," he told Deutsche Welle.

Within a few years, Jean-Paul Kneib said, this new method could give scientists a much clearer view of dark energy and possibly confirm the presumed fate of the universe: that it will expand forever at an ever-increasing rate.

"In this measurement we study only one cluster, but there's, like, many thousands of clusters," Kneib said. "By using this new technique using different clusters, we believe we can improve by a very large amount the accuracy on the measurement of the acceleration of the universe."

Author: Chelsea Wald

Editor: Cyrus Farivar

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