Laniakea and the Great Attractor

The idea is a watershed. On Earth, a drainage basin is defined not by a fence but by which way the rain runs: every drop that flows to the same river mouth belongs to the same basin. Brent Tully's team applied the same logic to galaxies. Using the Cosmicflows survey of galaxy velocities, they mapped which way each galaxy is drifting once the overall expansion of the universe is subtracted, and drew the boundary where the flows diverge.

The result is Laniakea — Hawaiian for 'immense heaven' — about 160 megaparsecs (500 million light-years) across and home to roughly 100,000 galaxies. Our Virgo Supercluster, once thought to be the whole neighbourhood, turns out to be a single outlying lobe of it. Everything within Laniakea is slowly streaming toward one gravitational low point.

That focus is the Great Attractor, a mass concentration around the Norma Cluster (Abell 3627), roughly 65 megaparsecs away. It is awkward to study because it lies behind the dense star clouds and dust of the Milky Way's own disc — the 'Zone of Avoidance' — so much of what we know comes from radio and infrared surveys that see through the obscuration, and from the galaxy motions themselves.

It does not end there. Laniakea itself is not at rest: the whole supercluster, along with its neighbours, is caught in a broader flow toward an even greater concentration of mass beyond its border — the Shapley Concentration, the densest known collection of galaxy clusters in the nearby universe. A basin within a slope.

And there is a twist in the tail. These flows built up over billions of years, but dark energy now drives the universe's expansion to accelerate. Over cosmic time that acceleration wins: Laniakea is not gravitationally bound and will not collapse into a single object. It is a snapshot of a flow, not a structure that will endure — a useful way to name our place, not a permanent home.