July 10, 2012
Scientists Detect Dark Matter Skeleton Of The Universe
Lee Rannals for redOrbit.com - Your Universe Online
For the first time, scientists have detected part of the invisible dark matter skeleton of the universe, where over half of all matter is believed to reside.
The discovery confirms a key prediction in the theory of how the universe's current web-like structure came to be.
The map of the known universe shows that most galaxies are organized into clusters, but some are situated along filaments that connect to the clusters.
Cosmologists believe dark matter resides underneath those filaments, which help serve as cosmic highways, guiding galaxies toward the gravitational pull.
Dark matter's contribution had been predicted with computer simulations, and its shape had been routed out based on the distribution of the galaxies.
“We found the dark matter filaments. For the first time, we can see them,” JÃ¶rg Dietrich, a physics research fellow in the University of Michigan College of Literature, Science and the Arts, said in a press release.
Dark matter doesn't emit or absorb light, so astronomers are unable to see it directly with telescopes. Scientists believe it exists based on how its gravity affects visible matter. Dark matter is thought to make up more than 80 percent of the universe.
In order to "see" the dark matter, the researchers had to take advantage of a phenomenon known as gravitational lensing.
The gravity of massive objects like galaxy clusters act as a lens to bend and distort the light from more distant objects. The team observed tens of thousands of galaxies beyond the supercluster.
They were able to determine the extent at which the supercluster distorted galaxies so they could plot the gravitational field and the mass of the Abell 222 and 223 clusters.
“It looks like there´s a bridge that shows that there is additional mass beyond what the clusters contain,” Dietrich, who was the lead author in the paper published in Nature, said in the release. “The clusters alone cannot explain this additional mass."
Before Dietrich's discovery, scientists assumed that the gravitational lensing signal would be strong enough to give away dark matter's configuration. However, the researchers focused on a peculiar cluster system whose axis is oriented towards Earth, which helped magnify the lensing effect.
“This result is a verification that for many years was thought to be impossible,” Dietrich said in the release.
The team also discovered a spike in X-ray emissions along the filament, due to an excess of hot, ionized matter being pulled by gravity toward the massive filament. They believe that 90 percent or more of the filament's mass is dark matter.