Mysterious dark matter is spread around the universe just like regular matter, according to a pair of new studies that bring cosmologists back to an old way of thinking that had been losing favor.
The studies show that both forms of matter work in concert to build delicate filaments in space, with dense junctions where galaxies cluster together, as seen on the grandest scales. The resulting structures look something like spider webs or sponges.
If correct, the work should help researchers understand how the first galaxies were born and how the universe evolved.
Dark matter is unseen stuff that must exist, scientists say, based on what they know about how galaxies and clusters of galaxies remain bound together by gravity. Some dark matter is
.But how and when did regular matter and dark matter begin to work together? Or, for that matter, did they ever learn to get along?
In one of the new studies, researchers compared the expected distribution of dark matter, based on complex mathematical predictions, to a relatively comprehensive catalogue of more than 200,000 galaxies known as the 2dF Galaxy Redshift Survey.
The result showed that on large cosmic scales -- across distances measured in tens of millions of light-years -- dark matter and galaxies trace out the same shapes and structures. They become sculpted into nearly identical sheets and filaments, with vast expanses of near-nothingness in between.
"The fine filamentary structure can only be explained by highly collapsed filaments of dark matter, which are traced out by the dots of the galaxies," said one of the lead researchers, Alan Heavens of the University of Edinburgh, via e-mail. "Other possibilities do not produce such elaborate patterns."
Heavens and Licia Verde of Rutgers University also compared several other theorized dark-matter distributions to the data in the 2dF survey, but none fit, said Matthew Colless of the Australian National University.
"This is not direct evidence for dark matter, but it is supportive in that it means that only the simplest relationship between galaxies and dark matter is needed to explain what we see," said Colless, who worked on the original 2dF survey and is a co-author of a paper by Heavens and Verde detailing the new findings.
The results, released Monday, are supported by a second study in which the 2dF survey was compared to separate measurements of the Cosmic Microwave Background, ubiquitous but subtle radiation left over from the Big Bang.
That study, led by Ofer Lahav and Sarah Bridle of Cambridge University, found "remarkable agreement" between the distribution of luminous galaxies and the distribution of overall mass on scales larger than 30 million light-years, the researchers said.
Firmer footing
John Arabadjis, an MIT expert in dark matter who was not involved in either study, called the collective work a significant step forward in understanding how this strange stuff is spread around.
It also represents a retracing of theoretical steps.
Arabadjis said that over the past decade or two, researchers had begun to doubt whether luminous matter and dark matter would create similar structures in space, as the new findings indicate.
"This result appears to bring the field back to where it once was, although on much firmer footing," Arabadjis told SPACE.com.
The work also adds vital data to a field that is dominated by computer simulations as opposed to actual observation, Arabadjis said.
No Big Crunch
The two studies also confirm previous findings showing there is not enough dark matter to stop the universe from expanding forever.
Some theorists had in recent years suggested that gravity might eventually reign in the current expansion of the universe, causing everything to fall back on itself in a Big Crunch.
The 2dF survey is a product of the Anglo-Australian telescope in New South Wales, Australia. Papers on the two new studies have been submitted for publication to the Monthly Notices of the Royal Astronomical Society.
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