The structure is a large quasar group — a collection of supermassive black holes which form a single, massive structure — and it is huge. It's made up of 73 quasars, and is over four billion light-years across at its widest point. For some perspective, that distance is 1600 times larger than the distance between our galaxy, the Milky Way, and its nearest neighbour, the Andromeda Galaxy. Dr Clowes, one of the researchers on the projects, explains:
"While it is difficult to fathom the scale of this large quasar group, 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."
The Cosmological Principle — the notion that "'viewed on a sufficiently large scale, the properties of the universe are the same for all observers" — is bread and butter to astronomers. But structures of this scale raise problems of perspective that could throw the idea into question. Regardless of how Einstein's thinking stands up, though, this is an amazing — and mind-boggling — discovery. [Royal Astronomical Society]