An international team of astronomers has found the largest known structure in the universe - a group of quasars four billion light years across.
Quasars are the nuclei of extremely ancient galaxies that can flare up brightly, making them visible across huge distances, for comparatively brief period of between 10 and 100 million years. They tend to group together in structures known as large quasar groups or LQGs. And the biggest of these, says the team, is enormous.
"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," says Dr Roger Clowes of the University of Central Lancashire.
"This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe."
Indeed, the structure is so big that it clalleges current theories of cosmology. The Cosmological Principle assumes that the universe, when viewed at a sufficiently large scale, looks the same no matter where it's observed from.
Based on this, and the modern theory of cosmology, calculations suggest that astrophysicists shouldn't be able to find a structure larger than 1.2 billion light years.
However, the newly-discovered LQG however has a typical dimension of 1.7 billion light years; and, because it's elongated, its longest dimension is four billion light years.
"Even travelling at the speed of light, it would take 4 billion light years to cross. This is significant not just because of its size but also because it challenges the Cosmological Principle, which has been widely accepted since Einstein," says Clowes.
"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."