A Field Guide to Laniakea
The Local Universe Organized by Cosmic Web Topology
4 Superclusters·27 Structural Regions·128 Galaxy Groups·~500 Mly
In 2014, Tully et al. defined Laniakea — a basin of attraction spanning approximately 500 million light-years that contains the Milky Way along with tens of thousands of other galaxies. Named "immeasurable heaven" in Hawaiian, Laniakea was mapped using velocity-watershed analysis of the Cosmicflows catalog: tracing how galaxies flow under gravity to identify dynamically coherent regions, much like mapping river drainage basins on Earth. The technique revealed that the Virgo Supercluster — long thought to be our home supercluster — constitutes only one lobe of a much larger structure.
This field guide proposes a hierarchical framework for organizing Laniakea's contents. The basin comprises four major supercluster lobes — Virgo, Hydra, Centaurus, and Pavo-Indus — each anchored by massive galaxy clusters, yet unified by convergent velocity flows toward a common gravitational core in the Norma-Centaurus region: the Great Attractor. The framework distinguishes basins of attraction (velocity-watershed-defined regions like Laniakea) from superclusters (the overdensity lobes within them), resolving a longstanding ambiguity in cosmographic terminology.
Rather than organizing galaxies by distance or brightness, the framework catalogs 128 galaxy groups containing approximately 718 galaxies into 27 structural regions defined by cosmic web topology — sheets, filaments, clusters, walls, streams, clouds, and void boundaries — prioritizing physical relationships and gravitational flow dynamics to reveal how structures relate within the flowing architecture of the cosmic web.
Laniakea's four superclusters exhibit convergent velocity flows toward the Great Attractor in the Norma-Centaurus region — the defining characteristic of the basin. The Virgo Supercluster flows southeastward toward this convergence point, Hydra and Centaurus contribute major flow streams from the south, and Pavo-Indus flows northward from the basin's far periphery. This convergent pattern, revealed through Cosmicflows velocity field analysis, demonstrates that these four superclusters are not independent structures but interconnected components of a unified dynamical system.
Virgo Supercluster
Hydra Supercluster
Centaurus Supercluster
