'Giant arc' stretching 3.3 billion light-years across the cosmos shouldn't exist

A newly discovered crescent of galaxies spanning 3.3 billion light-years is among the largest known structures in the universe and challenges some of astronomers' most basic assumptions about the cosmos.

The epic arrangement, called the Giant Arc, consists of galaxies, galactic clusters, and lots of gas and dust. It is located 9.2 billion light-years away and stretches across roughly a 15th of the observable universe. But the finding, which will take its place in the list of biggest things in the cosmos, undermines a bedrock expectation about the universe. Astronomers have long adhered to what's known as the cosmological principle, which states that, at the largest scales, matter is more or less evenly distributed throughout space.