Astrophysicists have discovered a galaxy made entirely of dark matter, in the Virgo constellation. Named VIRGOHI21, it is the first galaxy to be found that contains no stars. Dark matter is invisible, and scientists have never identified the particles that it is composed of, but they believe that it exists because of the gravitational pull they believe it exerts on normal, visible matter. This galaxy was identified when astrophysicists discovered a cloud of hydrogen atoms mysteriously swirling around an invisible centre, in the way they would around a normal galaxy of stars.
Gravity is the force that pulls stars and planets together, and the universe contains a great deal more gravity than can be accounted for by visible matter. Without any other way to explain this force, physicists have invoked the idea of “dark matter” to account for the universe’s “missing mass.” It appears that the universe contains five times more dark matter than visible matter. Astrophysicists have long thought that this abundant form of matter must play a huge role in shaping our universe, pulling visible matter into planets and stars and causing galaxies to form. Theories that explain how dark matter shapes the universe predict that the universe should contain more dark galaxies than visible ones. But until now dark galaxies have been a “thorn in the side” of scientists because they did not have any proof for the existence of dark galaxies. Now, with this finding, physicists will have an easier time understanding how our universe was formed.
Source: Nature
