Hundreds of Invisible "X" Galaxies Predicted Orbiting the Milky Way
The outer edges of the Milky Way's appear to be orbited by innumerable invisible galaxies, one of which appears to be crashing into our own. Back in 2005 astronomers discovered the first evidence of mysterious dark galaxies with no starlight - VIRGOHI 21 - a mysterious cloud of hydrogen in the Virgo Cluster 50 million light-years from the Earth found to be colliding with our galaxy - revealed its existence from radio waves from neutral hydrogen coming from a rotating cloud containing enough hydrogen gas to spawn 100 million stars like the sun and fill a small galaxy.
The rotation of VIRGOHI21 is far too fast to be consistent with the gravity of the detected hydrogen. Rather, it implies the presence of a dark matter halo with tens of billions of solar masses. Given the very small number of stars detected, this implies a mass-to-light ratio of about 500, far greater than that of a normal galaxy (which would be around 50). The large gravity of the dark matter halo in this interpretation explains the perturbed nature of the nearby spiral galaxy NGC 4254 and the bridge of neutral hydrogen extending between the two entities.
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