Reporting the finding in the journal Monthly Notices of the Royal Astronomical Society, the researchers led by scientists from the University of Central Lancashire described a large quasar group, made up of the nuclei of galaxies from the early days of the universe that undergo brief periods of extremely high brightness that make them visible across huge distances.
Since 1982 it has been known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes known as LGQs.
"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," researcher Roger Clowes said. "This is hugely exciting -- not least because it runs counter to our current understanding of the scale of the universe.
"This is significant not just because of its size but also because it challenges the Cosmological Principle, which has been widely accepted since Einstein."
The Cosmological Principle holds that the universe, when viewed at a sufficiently large scale, should look the same, more or less uniform, no matter where you are observing it from.
The Principle is assumed but has never been demonstrated observationally "beyond reasonable doubt," scientists 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.