The puzzling migration of matter in deep space ? dubbed"dark flow" ? has been observed at farther distances than ever before,scientists have announced.
Distant galaxy clusters appear to be zooming through spaceat phenomenal speeds that surpass 1 million mph. The clusters were tracked to 2.5billion light-years away ? twice as far as earlier measurements.
This motion can't be explained by any known cosmic force,the researchers say. They suspect that whatever's tugging the matter may lie beyondour observableuniverse.
The notion is a controversial one because it has only beenmeasured by one group of scientists in one set of data so far.
"We understand why this idea is so annoying attimes," said study leader Alexander Kashlinsky at NASA's Goddard SpaceFlight Center in Greenbelt, Md. "In fact, part of the motivation for ourongoing project was precisely to rule it out. But it is in the data, we don?tsee it going away. ?
Kashlinsky and colleagues first reported their measurementsof the darkflow in 2008. They measured signals of the movement in the leftover lightfrom the Big Bang, thought to have created the universe 13.7 billion years ago.That leftover light is called the cosmic microwave background (CMB) radiation.
The dark flow appears to be moving in the direction of the southernconstellations Centaurus and Hydra.
[See a video explaining dark flow.]
Over the universe?s horizon
The new study is based on a larger data set of about 1,500galaxy clusters and CMB measurements taken over five years by space andground-based telescopes. The researchers say their new results strengthenindications that the dark flow is real.
"It looks indeed that the entire observable universe ismoving with respect to the CMB radiation," Kashlinsky told SPACE.com."We can now say that more confidently than our initial supposition."
The researchers think dark flow may be caused by structuresthat lie beyond the horizon of our own universe. As odd as that may sound, somecosmologists think that our universe is actually only a bubble of space-timethat was created during a period of rapidcosmic expansion, called inflation, after the Big Bang. Other bubbles mayalso have been created where inflation took place at a different rate, andperhaps something in one of the other bubbles is tugging at our universe.
The researchers hope to further test the dark flow usingupcoming data expected from the Planck satellite, which launched last year.
Some potential support for the dark flow idea came from anindependent study that found a similar motion, albeit in individual galaxies,and not clusters of galaxy, Kashlinsky said.
That team ? which includes researchers Richard Watkins ofWillamette University in Salem, Ore., Hume Feldman of the University of Kansas,and Michael Hudson of Canada's University of Waterloo ? found a sampling ofgalaxies that also displayed a collective motion, which happened to be in thesame direction as the dark flow measured by Kashlinsky and team.
"We see the flow in the same direction, no questionabout it," Feldman said. "That is very odd, it's not what you wouldexpect."
But Feldman cautioned that his observations were notnecessarily of the same dark flow, since they were on a completely different scaleof relatively nearby objects.
"There's nothing in our flow that says that their flowdoes not exist," Feldman said. "On the other hand, there's nothing inour flow that says their flow does exist, except that it's in the samedirection."
Kashlinsky and colleagues' new findings are detailed in theMarch 20 issue of The Astrophysical Journal Letters.