(non-random patterns in peculiar velocity of galaxy clusters)
Dark flow is a particular pattern observed in the movement of some
nearby galaxy clusters suggesting some force independent of the
Hubble expansion, like gravity of some unknown
relatively compact but extremely massive object.
Evidence was announced in 2008 based upon Wilkinson Microwave Anisotropy Probe (WMAP) data
as well as galaxy-cluster data, and has since been debated.
The concept has inspired exotic explanations from astrophysicists
and others.
The general direction of the dark flow is somewhat toward the
Great Attractor, but they could be independent.