Giant Web of Dark Matter Connects Galaxy Clusters
Stars and galaxies don't crop up randomly in space. Astronomical maps developed over the last 30 years show that a large majority of the universe's galaxies are scattered throughout the cosmos in threads and sheets. And scientists have suggested that dark matter - a substance that is thought to make up 83 percent of the universe but does not absorb or give off any light or other radiation - connects the star map like interstate highways connected distant cities.
Now, they've observed this underlying web of in a swath of dark matter that bridges two huge star clusters called Abell 222 and Abell 333, which lie 2.7 billion light years away.
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The only way to detect dark matter is to look at its gravitational effect on light and visible matter around it. If something is pulling matter toward a point in space, there must be something there that can attract it through gravity.
"This is the first time [a dark matter filament] has been convincingly detected from its gravitational lensing effect," said astronomer Jörg Dietrich of the University Observatory Munich, in Germany, according to MSNBC. "It's a resounding confirmation of the standard theory of structure formation of the universe. And it's a confirmation people didn't think was possible at this point."
Simulations of the Universe on the largest scales show an unexpected resemblance to nerve cells in the human brain, with galaxy clusters playing the role of the cell body and thinner filaments of matter linking them like axons, reports Ars Technica.
This dark matter structure has now been observed after much searching and a bit of luck. The rare spatial geometry of this cluster allowed the team to see gravitational lensing caused by the tendrils of dark matter - the bending of light as it passes from distant galaxies beyond the filament through the dark matter.
Dietrich told Nature that this dark bridge is oriented so that most of its mass lies along the line of sight to Earth, enhancing the lensing effect.
"The standard wisdom is that the gravitational lensing of filaments is too weak to be detected with current telescopes," Dietrich told Space.com. "Only when we realized this system has such a peculiar geometry did we realize we have a chance."
The astronomers used archival observations from data collected by the Japanese Subaru telescope on Mauna Kea in Hawaii.
"The data was observed in 2001 and just had been sitting in the archive and no one ever used it," Dietrich told MSNBC. "It took a while for us to realize that this data is around."
This is a huge milestone in the understanding of how our universe is formed, and backs up theories that suggested that visible matter follows lines of dark matter that make up the backbone of the cosmos.
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