The current view of the universe holds that space is homogeneous and isotropic at the very large scale. That is, it should look smooth and featureless, like a sponge, although at smaller scales it's made up of clumps, filaments and voids. For a long time, the largest known structure in the universe has been the Sloan Great Wall, a gigantic band of galaxies stretching 1.38 billion light years, and it was thought that no bigger structures could exist.
But now, the current model is challenged by an even larger structure.
Light from the most distant quasar yet seen reveals details about the chemistry of the early universe.
CREDIT: ESO/M. Kornmesser
Astronomers have discovered the largest known structure in the universe, a clump of active galactic cores that stretches 4 billion light-years from end to end. The structure is a large quasar group (LQG), a collection of extremely luminous galactic nuclei powered by supermassive central black holes. This particular group is so large that it challenges modern cosmological theory, researchers said.
"While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire universe," lead author Roger Clowes, of the University of Central Lancashire in England, said in a statement. "This is hugely exciting, not least because it runs counter to our current understanding of the scale of the universe."
The newly discovered LQC is so enormous, in fact, that theory predicts it shouldn't exist, researchers said. The quasar group appears to violate a widely accepted assumption known as the cosmological principle, which holds that the universe is essentially homogeneous when viewed at a sufficiently large scale. Calculations suggest that structures larger than about 1.2 billion light-years should not exist, researchers said.
"Our team has been looking at similar cases which add further weight to this challenge, and we will be continuing to investigate these fascinating phenomena," Clowes said.