What’s the biggest thing in the universe?  That would be a cluster of quasars so large it would take a vehicle traveling at the speed of light 4 billion years to cross.

The structure, known as a Large Quasar Group, or LQG, is so massive scientists say it may challenge a fundamental principle of cosmology, laid out by Albert Einstein, which states that when viewed on a sufficiently large scale, the properties of the universe are the same for all observers.

“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,” astronomer Roger Clowes, with the University of Central Lancashire, said in a statement.

“This is hugely exciting, not least because it runs counter to our current understanding of the scale of the universe,” Clowes said.

At its widest point, the LQG is about 1,600 times greater than the distance between the Milky Way galaxy and its nearest neighbor, Andromeda, a span equal to about 2.5 million light-years, or 15 quintillion miles.

The research has been published in the journal Monthly Notices of the Royal Astronomical Society.