An article published in the journal “Astronomy & Astrophysics” describes the discovery of what was called the BOSS Great Wall, a supercluster more than a billion light years long and between 4.5 and 6.4 billion light years from the Earth. With an estimated mass of 10,000 times that of the Milky Way, it’s the largest supercluster discovered so far.

The name refers to the Baryon Oscillation Spectroscopic Survey (BOSS), an international collaboration which aims to map galaxies and quasars in the early universe. Typically galaxies are connected by gravitational bonds and form clusters, which in turn are connected in superclusters. They too can be connected in aligned structures that are called walls.

Over the past decades, they had identified some Great Walls, very impressive structures such as the Sloan Great Wall, discovered in 2003, or the one called CfA2, discovered in 1989. The BOSS Great Wall is even larger and is even bigger than Laniakea, the supercluster that includes the Milky Way.

Inside the BOSS Great Wall 830 galaxies were spotted but probably contains others that are too far or not bright enough to be seen by the telescopes used for the survey. The visible galaxies form four superclusters connected by massive hot gas filaments.

Someone has already defined the BOSS Great Wall the largest structure in the universe but on this point also came doubts and objections. The problems concern the issue of defining a set of superclusters as a single structure but also the comparison with other structures of different types.

Galaxies are grouped into larger structures based on the gravitational links between them but it’s not always easy to define their boundaries. The Laniakea supercluster which includes the Milky Way surrounds us so the galaxies that compose it are relatively close. In contrast, the galaxies of the BOSS Great Wall are distant, so much that only a part was detected and the search continues.

Really huge structures of other types have been identified, such as a ring of galaxies for a length of about 5 billions of light years. Perhaps the BOSS Great Wall can be defined as the structure with the highest total mass discovered so far.

These questions show the difficulties in assessing huge and heterogeneous cosmic structures. It’s precisely for these reasons that the research continue and studying the Great Walls is a help to map the entire universe and better understand its history from the Big Bang to its subsequent evolution.