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Darkish Matter Filament Between Galaxy Clusters Discovered

This story was updated on July 5 at 9:32 am EDT.

A huge chain of invisible dark matter was discovered throughout the universe between two galaxy clusters.

The filament forms a bridge between two giant clusters called Abell 222 and Abell 223, which are 2.7 billion light years away. The universe is believed to be filled with such threads of dark matter, a mysterious substance that cannot be seen and is only perceived by its attraction.

Scientists have previously tried to find filaments of dark matter, which are predicted by theories that suggest that clusters of galaxies form at the intersections of filaments. It is believed that dark matter makes up 83 percent of all matter in the universe.

“This is the first time [a dark matter filament] was convincingly demonstrated by its gravitational lens effect, “said the astronomer Jörg Dietrich from the Munich University Observatory in Germany.” This is a resounding confirmation of the standard theory of the structure formation of the universe. And it’s an affirmation that people didn’t think was possible at the time. “

Many astronomers thought filament detection would have to wait until the telescopes were much more advanced, but Dietrich and his colleagues benefited from the rare spatial geometry of this cluster, which enabled them to see signs of what is known as a weak gravitational lens. [Gallery: Dark Matter Throughout the Universe]

According to Albert Einstein’s general theory of relativity, massive objects distort space and time around them, causing everything that travels through them, including light, to follow a curved path.

When light from a background object such as a galaxy passes near a massive cluster on its way to Earth, its image appears warped due to the crooked path its light has traveled.

“The usual wisdom is that the gravitational lens of filaments is too weak to be recognized with current telescopes,” Dietrich told SPACE.com. “It was only when we realized that this system had such a strange geometry that we realized that we had a chance.”

Abell 222 and Abell 223 are arranged so that they appear very close to the sky, but are further apart along our line of sight and facing away from the earth. This means that most of the system’s mass is condensed into a small area of ​​the sky through which any light coming from behind the earth must pass, thereby amplifying the gravitational lens signal.

The astronomers used observations from the public archive of data collected by the Japanese Subaru telescope on Mauna Kea, Hawaii.

“The data was observed in 2001 and had just sat in the archive and no one has ever used it,” said Dietrich. “It took us a while to find out that this data was there.”

Although the gravitational lens was too weak to be seen by the naked eye, the team used statistical analysis of light from more than 40,000 background galaxies to determine that the invisible mass between the two galaxy clusters distorted space-time.

The work follows on from a study by Dietrich from 2008, in which hot gas was found in the area of ​​the filament, which indicates its existence. However, this study did not detect any signal from the dark matter directly.

The researchers would like to look for dark matter filaments near other galaxy clusters, but say they haven’t found any good candidates that could make the lens powerful enough to be seen from Earth.

Editor’s Note: This article has been modified to correct the percentage of all matter in the universe that is dark matter, which is 83 percent, not 98 percent.

Follow Clara Moskowitz on Twitter @ClaraMoskowitz or SPACE.com @Spacedotcom. We are also on Facebook & Google+.

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