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