Straight after the largest spiral galaxy in the universe comes the largest anything in the universe, a formation stretching four billion light years. The structure is larger than anything ever seen and larger than what astronomers thought possible.In fact, its discovery puts into question our understanding of the universe at the macro level as well as its evolution.
The structure is a large quasar group (LQG), known to be the biggest thing in the universe. But this one, dubbed the Huge Large Quasar Group (H-LQG), takes the top spot.
It's got the biggest number of quasars inside, 73 of them, spread out over huge distances. While it's only 500 Mpc, or some 1.63 billion light years, it's 1240 Mpc, over four billion light years at its longest.
The group has a redshift of about 1.27 and is part of the early universe, at some 8,7 billion light years away. To give you a comparison, the observable universe is estimated at about 28,000 Mpc or 93 billion light years.
Astronomers weren't expecting to find such a large object and it threatens the validity of the cosmological principle which says that the universe, at a large enough scale, is rather uniform.
More broadly, it assumes that the laws of physics don't change in different parts of the universe.
The long held belief was that such large structures couldn't form, particularly in the early universe, but the new evidence contradicts the assumption and previous calculations of how big a structure could get. The upper limit is believed to be 1.2 billion light years, which the H-LQG obviously violates.
Large quasar groups, as the name suggests, are groups of quasars that have clumped together. Since quasars are only active a relatively brief period of time, these groups in which all quasars are active are linked together.