Mysterious cosmic 'dark flow' tracked deeper into universe

Washington, March 11 : A new study has tracked the mysterious cosmic 'dark flow' to twice the distance originally reported in the Universe.

The study was led by Alexander Kashlinsky at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"This is not something we set out to find, but we cannot make it go away," Kashlinsky said.

"Now we see that it persists to much greater distances - as far as 2.5 billion light-years away," he added.

The clusters appear to be moving along a line extending from our solar system toward Centaurus/Hydra, but the direction of this motion is less certain.

Evidence indicates that the clusters are headed outward along this path, away from Earth, but the team cannot yet rule out the opposite flow.

"We detect motion along this axis, but right now our data cannot state as strongly as we'd like whether the clusters are coming or going," Kashlinsky said.

The new study builds on a previous one by using the five-year results from WMAP and by doubling the number of galaxy clusters.

"It takes, on average, about an hour of telescope time to measure the distance to each cluster we work with, not to mention the years required to find these systems in the first place," said Harald Ebeling at the University of Hawaii. "This is a project requiring considerable followthrough," he added.

According to Fernando Atrio-Barandela at the University of Salamanca, Spain, who has focused on understanding the possible errors in the team's analysis, the new study provides much stronger evidence that the dark flow is real.

For example, the brightest clusters at X-ray wavelengths hold the greatest amount of hot gas to distort CMB photons.

"When processed, these same clusters also display the strongest KSZ signature - unlikely if the dark flow were merely a statistical fluke," he said.

In addition, the team, which now also includes Alastair Edge at the University of Durham, England, sorted the cluster catalog into four "slices" representing different distance ranges.

They then examined the preferred flow direction for the clusters within each slice.

While the size and exact position of this direction display some variation, the overall trends among the slices exhibit remarkable agreement.

The researchers are currently working to expand their cluster catalog in order to track the dark flow to about twice the current distance. Improved modeling of hot gas within the galaxy clusters will help refine the speed, axis, and direction of motion.