January 12, 2013
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 bysupermassive 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 hugelyexciting , not least because it runs counter to our current understanding of the scale of the universe .”
Quasars  are the brightest objects in the universe. For decades, astronomers have known that they tend to assemble in huge groups, some of which are more than 600 million light-years wide.