Astronomers Perplexed by "Dark Flow"

NASA photo of galaxy cluster 1E 0657-56 lying 3.8 billion light-years away. It's one of hundreds that appear to be carried along by a mysterious cosmic flow.

Here’s today’s second post sounding like something from Sci-Fi: This time it’s strange patches of dark matter moving through the universe, at high speeds and in a uniform direction, with nothing in the observable universe propelling them.

Astronomers are calling the phenomenon “dark flow.” According to an article on Space.com:

Scientists discovered the flow by studying some of the largest structures in the cosmos: giant clusters of galaxies. These clusters are conglomerations of about a thousand galaxies, as well as very hot gas which emits X-rays. By observing the interaction of the X-rays with the cosmic microwave background (CMB), which is leftover radiation from the Big Bang, scientists can study the movement of clusters.

The X-rays scatter photons in the CMB, shifting its temperature in an effect known as the kinematic Sunyaev-Zel'dovich (SZ) effect. This effect had not been observed as a result of galaxy clusters before, but a team of researchers led by Alexander Kashlinsky, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., found it when they studied a huge catalogue of 700 clusters, reaching out up to 6 billion light-years, or half the universe away. They compared this catalogue to the map of the CMB taken by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite.

They discovered that the clusters were moving nearly 2 million mph toward a region in the sky between the constellations of Centaurus and Vela. This motion is different from the outward expansion of the universe (which is accelerated by the force called dark energy).

"We found a very significant velocity, and furthermore, this velocity does not decrease with distance, as far as we can measure," Kashlinsky told SPACE.com. "The matter in the observable universe just cannot produce the flow we measure."

The scientists deduced that whatever is driving the movements of the clusters must lie beyond the known universe.

Click here for the complete Space.com article.