From National Geographic…

The researchers had expected to find that, the farther away clusters are, the slower they appear to be moving.

Instead, Kashlinsky said, “We found a great surprise.”

The clusters were all moving at the same speed—nearly 2 million miles (3.2 million kilometers) an hour —and in a single direction.

Though this dark flow was detected only in galaxy clusters, it should apply to every structure in the known universe, Kashlinsky said.