The presence of a large underdensity, the dipole repeller, is predicted based on a study of the velocity field of our Local Group of galaxies. The combined effects of this super-void and the Shapley concentration control the local cosmic flow.
Our Local Group of galaxies is moving with respect to the cosmic microwave background (CMB) with a velocity 1 of V CMB = 631 ± 20 km s−1 and participates in a bulk flow that extends out to distances of ~20,000 km s−1 or more
Source: The dipole repeller
Figure 1: A face-on view of a slice 6,000 km s−1 thick, normal to the direction of the pointing vector rˆ=(0.604,0.720,−0.342).
Three different elements of the flow are presented: mapping of the velocity field is shown by means of streamlines (seeded randomly in the slice); red and grey surfaces present the knots and filaments of the V-web, respectively; and equi-gravitational potential (ϕ) surfaces are shown in green and yellow. The potential surfaces enclose the dipole repeller (in yellow) and the Shapley attractor (in green) that dominate the flow. The yellow arrow originates at our position and indicates the direction of the CMB dipole (galactic longitude l = 276°, galactic latitude b = 30°). The distance scale is given in units of km s−1.
Figure 2: A 3D view of the velocity field.
It is shown here by means of the flow streamlines (in black–blue, left panel) and of the anti-flow (in yellow–red, right panel). Anti-flow is defined here by the negative (namely, the reverse) of the velocity field. The same streamlines are seeded on a regular grid and are coloured according to the magnitude of the velocity. The flow streamlines diverge from the repeller and converge on the attractor. For the anti-flow, the divergence and convergence switch roles: they diverge from the attractor and converge on the repeller. The knots and filaments of the V-web are shown for reference. Cartesian supergalactic coordinates (SGX, SGY, SGZ) are assumed here. (For a 3D view, look at the accompanying Supplementary Video, at time 00:56–01:28.)