The Milky Way and neighboring Andromeda Galaxy are being propelled rapidly through space by an intergalactic void, according to a study that used 3D mapping to depict the motion of galaxies in our galactic neighborhood.
Scientists have long known that the Milky Way and Andromeda are speeding toward several clusters of galaxies known as the Great Attractor at 1.4 million miles per hour but were uncertain as to the cause of this motion.
Instead of looking at the distribution of galaxies in the Milky Way’s neighborhood, a research team decided to study the motion of all galaxies by creating a 3D map of their flow field.
That map enabled them to deduce the distribution of both stars and dark matter, which revealed extremely dense regions pulling on the Milky Way as well as a very low dense area with few stars pushing our galaxy.
The notion that a void could be propelling the Milky Way through space has been previously proposed, but this is the first time scientists have found evidence for it.
Other theories that sought to explain our galaxy’s motion include the gravitational pull of the Great Attractor and the gravity of an even larger, denser stellar field 600 light years away in the same direction, known as the Shapley Concentration.
Yet neither of those could satisfactorily explain the motion of the Milky Way and Andromeda.
“Through 3D mapping the flow of galaxies through space, we found that our Milky Way galaxy is speeding away from a large, previously unidentified, region of low density that we call the Dipole Repeller, as well as towards the known Shapley Concentration,” explained Yehuda Hoffman of the Hebrew University Racah Institute of Physics.
“It has become apparent that push and pull are of comparable importance at our location.”
An extremely large region more than a billion light years across, which amounts to one-tenth the radius of the entire observable universe, is moving away from the low-density void toward the Shapley Concentration.
Within this region, the research team also located the Laniakea galactic supercluster.
Previous studies of the distribution of galaxies that emit X-rays suggested the presence of the void but did not provide conclusive evidence for it, said R. Brent Tully of the Institute for Astronomy (IfA) at the University of Hawaii.
Confirmation of the void’s existence explains both the direction and velocity of the Milky Way and Andromeda.
As a next step, scientists hope to observe and identify the small galaxies in the void in optical, near-infrared, and radio wavelengths.
The study’s findings were published in the journal Nature Astronomy.