Dark Flow: Anomalous Bulk Motion of Galaxy Clusters

Some surveys of distant galaxy clusters report a small coherent drift on top of the ordinary Hubble expansion — a "dark flow" that does not average away across the sky the way random peculiar velocities should. This simulator scatters a configurable number of galaxy clusters through a 3D volume, gives each one an outward Hubble-flow velocity plus a peculiar-velocity component built from a shared coherent vector and independent per-cluster noise, and then runs the same vector-averaging estimator real surveys use to try to recover that coherent vector from the noisy individual measurements. Tune the injected flow speed, the noise dispersion, and the sample size to see directly how averaging over more clusters suppresses random noise (∝ 1/√N) while a genuinely coherent signal survives.