Astronomers have discovered the largest object in the universe.
In fact it's so big, it might challenge a key principle of cosmology predicted by none other than Einstein himself.
The object is a group of quasars from that four billion light years across.
Together they form the largest structure in the universe, researchers at the University of Central Lancashire reported in the journal of the Royal Astronomical Society.
The quasar structure is more than 1,600 times as big as our galaxy, the Milky Way.
It's also roughly 24 sextillion miles, or the length of 3,240 sextillion London buses.
It has been known for more than 20 years that quasars - the nuclei of galaxies from the early history of the universe - tend to gather together in "clumps".
But this cluster - the Large Quasar Group - is far bigger than any previously discovered.
It is so massive that it might prove tricky for the Cosmological Principle, established by Einstein, that on very large scales the universe looks the same no matter where you observe it from.
The Royal Astronomical Society explains:
To give some sense of scale, our galaxy, the Milky Way, is separated from its nearest neighbour, the Andromeda Galaxy, by about 0.75 Megaparsecs (Mpc) or 2.5 million light-years.
Whole clusters of galaxies can be 2-3 Mpc across but LQGs can be 200 Mpc or more across. Based on the Cosmological Principle and the modern theory of cosmology, calculations suggest that astrophysicists should not be able to find a structure larger than 370 Mpc.
The LQG is about 1,200 Mpc across - or four times larger than it should be.
Dr Roger Clowes, who led the study, 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. This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe.
"Even travelling at the speed of light, it would take 4 billion 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. 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."