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 space at phenomenal speeds that surpass 1 million mph. The clusters were tracked to 2.5 billion 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 beyond our observable universe.
The notion is a controversial one because it has only been measured by one group of scientists in one set of data so far.
“We understand why this idea is so annoying at times,” said study leader Alexander Kashlinsky at NASA’s Goddard Space Flight Center in Greenbelt, Md. “In fact, part of the motivation for our ongoing project was precisely to rule it out. But it is in the data, we don’t see it going away.”
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Kashlinsky and colleagues first reported their measurements of the dark flow in 2008. They measured signals of the movement in the leftover light from 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 southern constellations Centaurus and Hydra.
Over the universe’s horizon
The new study is based on a larger data set of about 1,500 galaxy clusters and CMB measurements taken over five years by space and ground-based telescopes. The researchers say their new results strengthen indications that the dark flow is real.
“It looks indeed that the entire observable universe is moving 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 structures that lie beyond the horizon of our own universe. As odd as that may sound, some cosmologists think that our universe is actually only a bubble of space-time that was created during a period of rapid cosmic expansion, called inflation, after the Big Bang. Other bubbles may also have been created where inflation took place at a different rate, and perhaps something in one of the other bubbles is tugging at our universe.
The researchers hope to further test the dark flow using upcoming data expected from the Planck satellite, which launched last year.
Other evidence
Some potential support for the dark flow idea came from an independent study that found a similar motion, albeit in individual galaxies, and not clusters of galaxy, Kashlinsky said.
That team — which includes researchers Richard Watkins of Willamette University in Salem, Ore., Hume Feldman of the University of Kansas, and Michael Hudson of Canada’s University of Waterloo — found a sampling of galaxies that also displayed a collective motion, which happened to be in the same direction as the dark flow measured by Kashlinsky and team.
“We see the flow in the same direction, no question about it,” Feldman said. “That is very odd, it’s not what you would expect.”
But Feldman cautioned that his observations were not necessarily of the same dark flow, since they were on a completely different scale of relatively nearby objects.
“There’s nothing in our flow that says that their flow does not exist,” Feldman said. “On the other hand, there’s nothing in our flow that says their flow does exist, except that it’s in the same direction.”
Kashlinsky and colleagues’ new findings are detailed in the March 20 issue of The Astrophysical Journal Letters.
You are here: the mysterious architecture of the universe – in pictures
The Earth seen from the moon
Astronomers measure distances by the time it takes light to travel across them. The light captured in this image of the Earth took about 1.3 seconds to travel to the Apollo astronauts holding the camera, so astronomers say the moon is 1.3 light seconds away. We must move outward to larger realms to find the cosmic web of galaxies
Photograph: Nasa
The solar system
Here we see the almost-circular orbits of the outer planets – Jupiter, Saturn, Uranus and Neptune – edge on. Neptune’s orbit measures eight light hours across. The Earth’s orbit is only 1/5th the size of Jupiter’s, measuring only 16 light minutes in diameter, too small to be seen in this picture. Instead we can see the elliptical orbits of Halley’s comet and the icy Kuiper-belt objects Pluto, Eris, and Sedna. The distance from the sun to the nearest star is much, much bigger. Instead of minutes or hours, it takes four years for light to reach Alpha Centauri
Photograph: JR Gott and RJ Vanderbei, Sizing up the Universe, 2010
Simulated view of the Milky Way galaxy as seen from above
The Milky Way galaxy, where we live, is even bigger still. It measures 100,000 light years across and contains 300bn stars. Within the range of the Hubble space telescope are 130bn other galaxies. But how are these galaxies arranged in space? What is the architecture of the universe?
Photograph: Nasa
The Bullet Cluster
Galaxies appear in clusters. The Bullet Cluster, which is 3.7bn light years away, formed when two clusters of galaxies collided and passed straight through each other. The debris from the collision can be seen glowing with x-rays and is shown here in red between the clusters, while the dark matter thought to hold each cluster together is indicated in blue
Photograph: Nasa
The honeycomb model
During the cold war, the Soviet school of cosmology favoured a high-density connected honeycomb of galaxies punctuated by isolated empty voids.The American school, by contrast, held that galaxies are arranged in isolated clusters spread through a low-density sea, like meatballs floating in a thin soup
Photograph: AP Roberts/EJ Garboczi/Acta Materialia
My high-school science project
Cosmic inflation suggests large-scale structure comes from random quantum fluctuations in the early universe. I realised this means high- and low-density fluctuations must have an equivalent geometry. This is a feature of sponge-like geometry, as I knew because of a high-school science project on sponge-like polyhedra that I took to Japan. Adrian Melott, Mark Dickinson and I showed how gravity grows initial fluctuations into a cosmic sponge, with filaments of galaxies connecting great clusters of galaxies and tunnels connecting low-density voids: the cosmic web
Photograph: JR Gott
The cosmic sponge
Studies of large scale-structure by our topology group progressed to larger and larger regions over the years. All showed high-density regions with a spongelike topology as depicted by this pair of observational samples from the Sloan Digital Sky Survey (2006) containing over 400,000 galaxies
Photograph: Adapted from: JR Gott et al, Astrophysical Journal, 675: 16, 2008
Prominent filaments in the cosmic web
Each dot in this image shows a galaxy, with the Earth at the very bottom. The CfA2 Great Wall stretches across the lower section, a structure about 300bn light years away from Earth that is 758m light years long, making it the largest known structure in the universe when it was discovered in the late 1980s by Margaret J Geller and John Huchra. At the top is the Sloan Great Wall, a formation about 1bn light years away that measures 1.37bn light years across, which I found with Mario Jurić in 2003
Photograph: Adapted from: JR Gott, Mario Juric, et al, Astrophysical Journal, 624: 463, 2005
Millennium Run computer simulation showing the cosmic web
This computer simulation of galaxy clustering run by a European consortium in 2005 shows a web of filaments connecting clusters. This reproduces closely the types of galaxy filaments connecting clusters which we see through telescopes – as shown in the previous image
Photograph: Volker Springel and the Virgo Consortium, Nature, 435: 629, 2005
Our view of the cosmic web
This all-sky infrared survey shows our Milky Way galaxy in the foreground, seen edge on from our position within the disk, with distant galaxies seen as dots in the background. The giant filaments seen here are the traces of tiny quantum fluctuations that took place in the tiniest blink of an eye right at the dawn of the universe 13.8bn years ago. These submicroscopic variations are now written in letters of almost unthinkable size all the way across the sky, and we have managed to read them
Photograph: 2MASS survey: T Jarrett, IPAC / Caltech
