The dipole repeller is a center of effective repulsion in the large-scale flow of galaxies in the neighborhood of the Milky Way, first detected in 2017. It is thought to be represented as a large supervoid, the Dipole Repeller Void.
Discovery
The Local Group of galaxies is moving relative to the cosmic microwave background at. There is also a pattern of bulk flow in the motion of neighboring galaxies extending to distances of over 250 megaparsecs. There is a known overdensity – the Shapley Supercluster – creating an attraction in the flow of galaxies. The repeller appears to be located at a distance of about 220 Mpc and is anticipated to coincide with a void in galaxy density. That single center of attraction along with a roughly equal single repeller appear to be the most significant contributors to the CMB dipole. The authors of the article published in Nature Astronomy in January 2017 argue that the distance velocity measurements of the Dipole Repeller are incompatible with an explanation based solely on an attractivegravitational force. No single observed concentration of matter can explain the observed velocities and directions of distance from stars and galaxies. We can therefore observe the presence of an additional force, repulsive and whose nature is not specified, according to these authors: One of the authors, Hoffman, told The Guardian : Hoffman also told Wired: Hoffman told IFLScience : The CNRS shared the same position and stated in a press release: The same research team identified in September 2017 a second void with repulsive force : the Cold Spot Repeller. These voids, which repel by the inverse gravitational force, are among main components of the cosmic "V-Web".
Controversy about the Dipole Repeller and its observed repulsive force
Nevertheless, the discovery of the Dipole Repeller was commented on by astrophysicists and journalists in the mainstream media without using repulsive force. This is the case of Peter Coles, author of the blog "In the dark", Ethan Siegel in an article published by Forbes, as well as in an article published by Ars Technica. This is because gravitation is an attractive force, but if there is an underdense region it apparently acts as a gravitational repeller, based on the concept that there may be less attraction in the direction of the underdensity, and the greater attraction due to the higher density in other directions acts to pull objects away from the underdensity; in other words, the apparent repulsion is not an active force, but due simply to the lack of a force counteracting the attraction.
