Unique Dark Matter Structure Spotted

I would link to the article but this is from an email Los Alamos sent me:

Astronomers using NASA's Hubble Space Telescope have discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two galaxy clusters. Dark matter makes up most of the universe's material. Ordinary matter, which makes up stars and planets, comprises only a small percent of the universe's matter. The ring's discovery is among the strongest evidence yet that dark matter exists.

Astronomers have long suspected the existence of the invisible substance and theorized that it is the source of additional gravity that holds galaxy clusters together. Such clusters would fly apart if they relied only on the gravity from their visible stars. Although astronomers do not know what composes dark matter, they hypothesize that it is a type of elementary particle that pervades the universe.

"This is the first time we have detected dark matter as having a unique structure that is different from both the gas and the galaxies in the cluster," said astronomer M. James Jee of Johns Hopkins University in Baltimore. Jee is a member of the team that spotted the dark matter ring.

The ring, which measures 2.6 million light-years across, was found in the cluster CL0024+17, located 5 billion light-years from Earth. The team unexpectedly found the ring while it was mapping the distribution of dark matter within the cluster. Although astronomers cannot see dark matter, they can infer its existence in galaxy clusters by observing how its gravity bends the light of more distant background galaxies. During the team's analysis, they noticed a ripple in the mysterious substance, somewhat like the ripples created in a pond from a stone plopping into the water.

Jee said, "Although the invisible matter has been found before in other galaxy clusters, it has never been detected to be so largely separated from the hot gas and the galaxies that make up galaxy clusters. By seeing a dark matter structure that is not traced by galaxies and hot gas, we can study how it behaves differently from normal matter."

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The team's paper has been accepted for publication in the June 1 issue of Astrophysical Journal.

To learn more about the Hubble Space Telescope, including images and more information about dark matter ring in cluster CL0024+17, visit:

http://www.nasa.gov/hubble