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This galaxy is made of 99.99% dark matter

Image: Dragonfly 44
The dark galaxy Dragonfly 44 appears to have about as much mass as our own Milky Way galaxy, but only 0.01 percent of that mass is in the form of stars and normal matter. The rest is dark matter, scientists say. (Credit: Pieter van Dokkum and Roberto Abraham / Gemini Observatory / AURA)

About 85 percent of the mass of the universe consists of mysterious stuff known as dark matter, but a galaxy called Dragonfly 44 appears to be even darker: 99.99 percent dark, according to newly published findings.

Dragonfly 44, which lies about 300 million light-years away in the Coma galaxy cluster, is the subject of a study published in the Astrophysical Journal Letters.

“It has so few stars that it would quickly be ripped apart unless something was holding it together,” Yale astronomer Pieter van Dokkum, the study’s lead author, said in a news release.

Van Dokkum and his colleagues tracked the motions of the stars in the galaxy using the Keck Observatory and the Gemini North telescope in Hawaii. The stars’ motions told the astronomers about the gravitational field surrounding Dragonfly 44.

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By Alan Boyle

Mastermind of Cosmic Log, contributing editor at GeekWire, author of "The Case for Pluto: How a Little Planet Made a Big Difference," president of the Council for the Advancement of Science Writing. Check out "About Alan Boyle" for more fun facts.

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