In the standard ( \Lambda CDM ) model of cosmology the universe has emerged out of an early homogeneous and isotropic phase .
Structure formation is associated with the growth of density irregularities and peculiar velocities .
Our Local Group is moving with respect to the cosmic microwave background ( CMB ) with a velocity of V _ { CMB } = 631 \pm 20 Â km s ^ { -1 } Â [ ] and participates in a bulk flow that extends out to distances of at least \approx 20 , 000 Â km s ^ { -1 } Â [ ] .
The quest for the sources of that motion has dominated cosmography since the discovery of the CMB dipole .
The implicit assumption was that excesses in the abundance of galaxies induce the Local Group motion [ ] .
Yet , underdense regions push as much as overdensities attract [ ] but they are deficient of light and consequently difficult to chart .
It was suggested a decade ago that an underdensity in the northern hemisphere roughly 15,000Â km s ^ { -1 } Â away is a significan factor in the local flow [ ] .
Here we report on kinematic evidence for such an underdensity .
We map the large scale 3D velocity field using a Wiener filter reconstruction from the Cosmicflows-2 dataset of peculiar velocities , and identify the attractors and repellers that dominate the local dynamics .
We show here that the local flow is dominated by a single attractor - associated with the Shapley Concentration - and a single previously unidentified repeller .
Multipole expansion of the local flow provides further support for the existence and role played by the attractor and repeller .
The bulk flow ( i.e .
dipole moment ) is closely ( anti ) aligned with the repeller at a distance of 16 , 000 \pm 4 , 500 Â km s ^ { -1 } .
The expansion eigenvector of the shear tensor ( i.e .
quadrupole moment ) is closely aligned with the Shapley Attractor out to \approx 7,000Â km s ^ { -1 } .
The close alignment of the local bulk flow with the repeller provides further support for its dominant role in shaping the local flow .
This Dipole Repeller is predicted to be associated with a void in the distribution of galaxies .