Astronomers Find Huge Dark Matter Galaxy

Science Jeanette Walsh
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Small galaxies that have very few visible stars and are almost completely composed of dark matter have been found before. Astronomers from the United States and Canada are the first to find a galaxy the size of the Milk Way that is 99.9 percent dark matter. The discovery was reported in the August 26, 2016, edition of the journal Astrophysical Journal Letters.

Dark matter is thought to compose 85 percent of the mass of the known universe. The newly discovered galaxy called VIRGOHI21 and named Dragonfly 44 by the astronomers who found it is located in the Coma constellation 300 million light-years from Earth. The researchers used observations from the Keck Observatory and the Gemini North telescope in Hawaii to confirm the existence and behavior of the new galaxy over a week.

The basis for the existence of dark matter is the gravitational effects seen throughout the Universe. The halo of dark matter that surrounds the Milky Way was the first dark matter reservoir discovered. The behavior of stars is changed by the mass of dark matter. Stars move faster if the stars are closer to large bodies of dark matter.

Dragonfly 44 is an extremely dark galaxy. The only stars in the galaxy exist on the periphery of the galaxy. The stars were observed to form clusters by the researchers. The speed at which the stars move is much faster than average and is an indication that the galaxy is almost totally dark matter.

Dark matter cannot be seen with any known frequency of light. Maps of dark matter close to the Milky Way have been constructed by observations of the behavior of stars in the exterior of the Milky Way. Intense arguments about the composition of dark matter have not been resolved to date.

The discovery of a huge galaxy that is mostly dark matter is seen as a confirmation that dark matter exists. Study of Dragonfly 44 is hoped to be able to reveal the physical composition of dark matter in the future.