In extragalactic astronomy and cosmology, a supercluster can be defined not by galaxy density alone but by the divergence of peculiar velocity fields: after subtracting the Hubble expansion from observed galaxy motions, the residual gravitationally driven flows form basins of attraction, and a supercluster is the volume whose flow lines converge on a common gravitational focus. The boundary between adjacent superclusters is therefore a watershed surface — the locus where neighboring flow fields diverge toward different attractors — which supplies the first operational, dynamics-based definition of the largest structures in the cosmic web. Applied to the Milky Way's environment, this criterion enlarges our home structure from the Virgo Supercluster to a far more massive basin (Laniakea) centered on the Great Attractor, of which the previously named local supercluster is only a peripheral appendage.
In extragalactic astronomy and cosmology, a supercluster can be defined not by galaxy density alone but by the divergence of peculiar velocity fields: after subtracting the Hubble expansion from obse…