At the instant of the Big Bang, the universe began its inflation. Expanding outwards in all directions faster than the speed of light before cooling and forming all the bodies we can observe now. For decades it was assumed that the velocity and distribution of galaxy clusters should be pretty even across the universe with respect to the Cosmic Microwave Background (CMB). It seems now that this is not the case!
The Wilkinson Microwave Anisotropy Probe measured the temperature at different regions of the sky, the radiant heat remaining from the Big Bang. It found a very peculiar result, a flow of galaxy clusters with velocities of 600/1000 kilometres per second toward a 20 degree patch of sky. The galaxies were moving towards a patch of sky between the constellations Vela and Centaurus.
Researchers believed that the motion may be toward a remnant of no longer visible regions of the universe before inflation. Telescopes cannot see events earlier than about 380,000 years after The Big Bang, when the universe became transparent from bright orange.
So in a sense, the mass that these galaxies are moving toward cannot be observed now and would be outside our observable universe and particle horizon. So the mass is at least 46 billion light years from us at a point we cannot see.
So what is this called? Dark flow. This combines the sum of the velocity predicted by Hubble's Law plus a small unknown dark velocity flowing in a common direction. This has been compared to The Great Attractor which is a gravitational mystery but thought to originate from a massive cluster of galaxies that other bodies gravitate towards.
The effect has been measured to a distance of around 2.5 billion light years but research is ongoing to find the proper distance the dark flow influence extends to. NASA also have an opinion on the matter, they believe it could be the influence of another sibling universe just outside our own. The constant flow in the one direction doesn't seem to be a statistical fluke!
Here is an interesting thought, we can see galaxies merging through ground based telescopes and space telescopes. This could hypothetically mean that we could be merging with another universe! Tracking the direction of our own galaxy and our nearest neighbour Andromeda, it is clear both galaxies will merge. Maybe merging occurs on a universal scale too!