The visible edge of the universe is, by definition, the most distant thing that we can see. That does not mean it is the most distant thing we can feel, however.
According to astrophysicist Alexander Kashlinsky of NASA’s Goddard Space Flight Center, something from way beyond the edge seems to be pulling powerfully on galaxies in our universe, yanking them along in a motion he calls “dark flow.”
Kashlinsky and his team noticed this phenomenon while studying the cosmic microwave background, radiation left over from just after the Big Bang. Giant clusters of galaxies scatter
the radiation in a way that makes it possible to determine how each cluster is moving. When Kashlinsky plotted those motions, he determined that the galaxies seem to be racing in a particular direction, roughly aligned with the constellation Centaurus. The phenomenon was so unexpected that he conducted an expanded survey, looking at more and brighter galaxy clusters.
The results, released last March, not only confirm the dark flow but extend its known reach. “This motion persists as far as we can
see,” Kashlinsky says.
Nothing in the known universe can account for the dark flow phenomenon. So Kashlinsky thinks the galaxies are responding to the pull of matter and energy lying beyond our cosmic horizon. That unseen stuff could be at least a thousand times farther out than the horizon and cause “a slight tilt to our universe,” he theorizes.
Kashlinsky plans to use the European Space Agency’s new Planck spacecraft to make refined measurements of the dark flow to better understand what is causing it.