The mysterious force that drives the patches of matter at incredible speeds and in uniform directions through space, which can't be explained by comparison to any known gravitational force, and which may also exist outside of the observable universe, was called "dark flow."

If you think you already know all there is to know about dark energy or its kin matter, here's another tricky one to keep you busy for a while. The new theoretical phenomenon of "dark flow" puzzles scientists as it comes to complete the dark matter – dark energy relationship. When we said it might be outside the observable universe, we were not necessarily referring to the lengths to which eyes or even the most advanced optical devices can see. These are limited anyway – no matter how advanced our techniques, they will never be able to see "past" the 13.7 billion light years distance, which corresponds to the time-space point where Big Bang created the universe. But, although there might be something beyond that point, we couldn't see it unless we somehow thwart the theory of the speed of light and thus create some observation tool that currently lies beyond the powers of our science.

So, the dark flow, was it? Well, experts observed it while analyzing the biggest structures of the space, the giant galaxy clusters (conglomerates of around a thousand galaxies, as well as X-ray-emitting hot gas). They study their movement in space by noticing the interaction between the X-ray and Big Bang's radiation remains called cosmic microwave background or CMB. Astrophysicist Alexander Kashlinsky and his team from NASA's Goddard Space Flight Center first found the kinematic effect Sunyaev-Zel'dovich (CMB temperature shifts caused by X-rays' photon scattering) applied to a galaxy cluster. The team came upon this strange phenomenon while studying a 700 cluster catalog comprising half the universe's clusters (up to 6 billion light years away) and comparing it to the CMB map drawn by NASA's WMAP satellite.

The finding resulted in discovering that the clusters race at about 2 million mph (3.2 million kph) towards an area of space found between Vela and Centaurus constellations. This motion is atypical to the outward universe expansion caused by the dark energy. The specialists concluded that the engine of this special movement must be beyond the observable universe. "We found a very significant velocity, and furthermore, this velocity does not decrease with distance, as far as we can measure," Kashlinsky reported to Space. "The matter in the observable universe just cannot produce the flow we measure."

In the outer regions (that we cannot see, remember?) of the time-space bubble that we live in due to the Big Bang, as explained by the inflation theory, space and time may be entirely different. It may not be filled with galaxies and other known forms of matter that only the specific features of our bubble (like the mass density pattern) were able to give birth to, but instead, massive structures may lie there, way bigger than anything present in our observable universe, exactly the type of bodies that scientists presume are influencing our galaxy clusters in the form of the dark flow.

As Kashlinsky shares, "The structures responsible for this motion have been pushed so far away by inflation, I would guesstimate they may be hundreds of billions of light years away, that we cannot see even with the deepest telescopes because the light emitted there could not have reached us in the age of the universe. Most likely to create such a coherent flow they would have to be some very strange structures, maybe some warped space time. But this is just pure speculation."