Laniakea redrew the map of home and wrote a question into it. The 2014 analysis of CosmicFlows peculiar velocities (Tully, Courtois, Hoffman and Pomarede, Nature) defined our supercluster not by galaxy counts but by flow: the basin of attraction within which peculiar velocities converge toward the Great Attractor region, spanning roughly 500 million light-years and containing on the order of 10^17 solar masses across 100,000 galaxies. Within it, the velocity field organizes into coherent strands, filamentary channels of correlated galaxy motion threading the basin like a watershed's tributaries, mapped with increasing detail in CosmicFlows-3 and -4 reconstructions, which have since suggested even larger embedding basins (Shapley's gravitational domain may swallow Laniakea whole).
The structure is kinematic, which is what makes it demanding: ΛCDM happily builds density filaments, but Laniakea's strands are velocity coherences, streams of galaxies sharing motion over tens to hundreds of megaparsecs, and the basin-scale flow amplitudes keep running hot against the model. The same CosmicFlows data yield bulk flows (the 400-to-600 km/s motions toward Shapley and beyond) at amplitudes and depths that linear ΛCDM perturbation theory assigns probabilities of a percent or less, and basin-of-attraction analyses find watershed volumes larger than the simulated distribution comfortably produces. A velocity field this organized, this deep, demands either more large-scale power than the model's initial conditions contain or sources of coherent motion it does not include.
The standing is a maturing flow-field challenge: the kinematic cartography is now precise enough to test against simulation ensembles, the basins keep coming in large, and the flows keep coming in fast, with CosmicFlows-5-era distance catalogs set to harden the comparison.