Scientists have found a structure so large that it undermines their understanding of the universe. It's a collection of quasars that measures a difficult-to-imagine 4 billion light-years across, Space.com reports. To put that in perspective, the entire Milky Way is about 100,000 light-years wide. Known as a "large quasar group" (LQG), the structure consists of a cluster of incredibly bright galactic nuclei powered by supermassive black holes.
LQGs are often gigantic—previous examples have clocked in at more than 600 million light-years across—but this new discovery is literally impossibly large. Astronomers have long accepted the "cosmological principle," the theory that the universe is homogenous if you zoom out far enough, and based on it calculated that nothing exceeding 1.2 billion light-years could exist. "It is difficult to fathom the scale of this LQG," says the lead of the team that found it. "We can say quite definitively it is the largest structure ever seen in the entire universe." (Read more large quasar group stories.)