Our home galaxy, the Milky Way, is being pushed across the universe by a large unseen force, according to new research. Although it may not seem like a friendly gesture, the newly discovered Dipole Repeller is actually helping our galaxy on its journey across the expanding universe.
Researchers have known that the galaxy was moving at a relative speed for the past 30 years, but they didn’t know why.
“Now we find an emptiness in exactly the opposite direction, which provides a ‘push’ in the sense of a lack of pull,” said Brent Tully, one of the study authors and an astronomer at the Institute for Astronomy in Honolulu. “In a tug-of-war, if there are more people at one end, then the flow will be toward them and away from the weaker side.”
What’s that? You didn’t realize our home galaxy was moving?
Think about it: Everything is moving. Earth is rotating on its axis and orbiting the sun. The sun and the rest of our solar system orbit the center of the Milky Way. The Milky Way, along with other galaxies in the Laniakea Supercluster, is racing through space at about 2 million kilometers per hour.
But this is no aimless journey of motion. Researchers have long believed that our galaxy was attracted to an area rich with dozens of clusters of galaxies 750 million light-years away, called the Shapley Concentration or Shapley Attractor.
“On average, galaxies are flying apart from one another due to the expansion of the universe,” Tully explained. “However, each one is experiencing gravitational tugs from neighbors that cause deviant motions — toward regions of high density and away from regions of low density. Our solar system is a tiny part of a galaxy we call the Milky Way. As our galaxy participates in a flow, we go along for the ride.”
With the aid of powerful telescopes, the researchers were able to create a 3-D map of galaxy flow. Galaxies like our Milky Way follow the distribution of matter, so they tend to flow away from sparse, empty regions in space and toward the crowded spots.
By mapping the flow, Tully and his colleagues found the Dipole Repeller.
“We found a flow pattern reminiscent of streams of water that are organized by gravity to run downhill,” Tully said. “In detail, we played a mathematical trick by inverting the sense of gravity to see where flows would terminate in this altered case. Flows ended at our Dipole Repeller.”
Luminous galaxies are overly dense and in mass concentration, which creates the pull of the Shapley Attractor. Now, the researchers believe that the Milky Way isn’t just being pulled. It’s receiving an equally helpful push from a cosmic void behind the Milky Way.
Because the Dipole Repeller is low in density, with just a few galaxies in its massive void, this empty region acts as a repellant force. The universe is full of repellers and attractors, but the brightness of the attractors is easier to detect. Due to their low density, repellers appear as dark, empty voids, no matter their size.
Little is known about the Dipole Repeller or the galaxies within it, but understanding more about it can increase our understanding of the universe and how it works.
