The Milky Way is part of a much vaster galactic network than previously thought. The galaxy drifts along in a stream of galaxies on the outskirts of a newly identified collection of galaxy clusters, a supercluster named Laniakea. This supercluster — whose name means “heaven immeasurable” in Hawaiian — holds the mass of 100 million billion suns within a region that spans about 520 million light-years.
Astrophysicist R. Brent Tully of the University of Hawaii in Honolulu and colleagues sifted through data describing the positions and velocities of over 8,000 galaxies to get a fresh look at the Milky Way’s place in space. After accounting for the motion caused by the expansion of the universe, the team created a three-dimensional view of how gravity molds the galaxy’s cosmic neighborhood.
The new map, published in the Sept. 4 Nature, reveals Laniakea’s boundaries and weblike framework. The Milky Way lies along one of the lines of that web, in a tributary feeding one of many galactic rivers. Those streams converge in a gravitational valley roughly 200 million light-years away near two massive galaxy clusters: Norma and Centaurus. Their combined gravity appears to be drawing in other galaxies and clusters within Laniakea, including the Milky Way.