What is the Dark Flow?

Answering another question sent in by a subscriber:

Can you tell us more about Dark Flow?

In 2008, a group of authors studying cosmic microwave background radiation discovered a rather strange pattern. According to their results, galaxy clusters are not moving randomly but in a coordinated manner.

The research paper states that at least 1,400 galaxy clusters have been found to move in the same direction. The area in which these galaxy clusters are moving is located in the constellations Centaurus and Hydra. The total length of this galaxy flow is about 3 billion light-years.

Colored dots show galaxy clusters at different distances from us. Blue is 0.8–1.2 billion light-years, green is 1.2–1.7 billion light-years, yellow is 1.3–2.1 billion light-years, and red is 1.3–2.5 billion light-years. The colored ellipses indicate the direction of movement of the dots of corresponding colors.

These results contradict modern cosmological ideas, particularly the Cosmological Principle, which states that there should be no preferred directions, axes of rotation, symmetries, boundaries, etc., in the universe.

Initially, this phenomenon was tried to be explained by the presence of some massive object beyond the observable universe, whose gravity acts on these star clusters and causes them to move in the same direction. However, this hypothesis also poorly fits into modern cosmology.

Dark Flow in an artist’s conception