According to astronomers at the University of Bonn in Germany, who made the discovery,
the structure of satellite galaxies and star clusters around the Milky Way is so vast that it reaches across a million light-years 10 times as wide as the Milky Way itself. Existing dark matter theories fail to explain the arrangement of these cosmic objects. As said study team member Pavel Kroupa, a professor of astronomy at the University of Bon their model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. They see this as the beginning of a paradigm shift, one that will ultimately lead their to a new understanding of the universe. Dark matter is an invisible substance that is thought to make up roughly 23 percent of the universe. Astronomers estimate that the Milky Way contains 300,000 million stars in addition to extensive “arms” of gas and dust that reach out in a flat disk extending from the galaxy’s central bar. A number of smaller satellite galaxies and tight spherical bundles of ancient stars, called globular clusters, orbit at different distances from the main part of the Milky Way. In the new study, researchers noted that the different objects are distributed in a plane at right angles to the Milky Way’s galactic disk. The massive, newly discovered structure stretches from as close as 33,000 light-years away from the center of the Milky Way to as far as 1 million light-years away from the center. By merging data from a range of sources to compile a census of our galaxy’s surroundings, the scientists found that the area around the Milky Way includes bright “classical” satellite galaxies, plus fainter galaxies that were more recently detected, and globular clusters. The astronomers were also surprised by the arrangement of the cosmic objects. As the different companions orbit around the Milky Way, they shed material, stars and sometimes gas, which leaves long streams along their path. The results of the new study show that this lost material is also aligned with the plane of the galaxies and globular clusters. Existing theories of dark matter cannot adequately explain this galactic configuration. The observations suggest that other forces caused the unexpected arrangement of satellite galaxies around the Milky Way. Astronomers think that the Milky Way collided with another galaxy in the distant past. The other galaxy lost part of its material, material that then formed our galaxy’s satellite galaxies and the younger globular clusters and the bulge at the galactic center. This companions are the debris of this 11-billion-year-old collision.