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| Photo: keckobservatory.org |
Astronomers have discovered a rare galaxy that appears to contain almost no dark matter, adding new evidence to one of the biggest mysteries in the universe. The galaxy, called DF9, was observed using the WM Keck Observatory in Hawaii, and is the third known galaxy that lacks dark matter.
The study, conducted by researchers from Yale University and published in the Astrophysical Journal, suggests that DF9 is part of a unique linear structure of faint galaxies that may have formed after a violent collision between galaxies.
Previous observations have identified two similar galaxies, DF2 and DF4, which appear to contain little or no dark matter. With the discovery of DF9, researchers believe that the three galaxies may have formed during the same high-speed cosmic collision that separated normal matter from dark matter.
Scientists believe the collision may have removed gas and dark matter from the original galaxies, leaving behind new galaxies made up mostly of ordinary matter. Researchers say this rare discovery provides stronger evidence that dark matter exists as a physical substance rather than being explained only by alternative theories of gravity.
To study DF9, astronomers used the Keck Cosmic Web Imager (KCWI) instrument at Keck Observatory to measure the motion of stars within the galaxy. Observations showed that DF9 has a mass of about 100 million times that of the Sun, which matches visible matter. If it contained a normal amount of dark matter, the galaxy would be expected to be about 100 times more massive.
