Used to be astronomers thought the Milky Way was all there was. Just one enormous galaxy filled with everything in space. American astronomer Edwin Hubble turned that view on its head, proving that galaxies external to the Milky Way were a thing. Moreover, these galaxies gathered into small groups which gathered into clusters. Multiple clusters connected via gravity across the light years to form giant webs of clusters called superclusters.
Superclusters are among the largest known structures in the universe, stretching across 500 million light years or more. There are an estimated 10 million of them. Some, like the Laniakea Supercluster of which the Milky Way is a member, are home to over 100,000 galaxies.
A team of astronomers recently used the VIMOS instrument on ESO’s Very Large Telescope to identify a gigantic proto-supercluster of galaxies forming in the early Universe, just 2.3 billion years after the Big Bang. Researchers gave it the name Hyperion after the Greek Titan god of heavenly light. It’s the largest and most massive structure to be found so early in the formation of the universe and appears to be an evolving early supercluster. Its mass is a million billion (1015) times that of the sun, surprisingly similar to nearby more “mature” superclusters. Astronomers were surprised that such an enormous structure was already in place when the universe was so young. Recall that the farther we look across space, the further back in time we see.
Located in the constellation Sextans the Sextant below the familiar outline of Leo the Lion, Hyperion was found by analyzing data obtained from the VIMOS Ultra-deep Survey which provided a 3D map of over 10,000 distant galaxies. VIMOS can measure the light of a hundred galaxies at the same time to determine their distances, speeds and other qualities.
Despite being as massive as mature superclusters, Hyperion has much different structure with at least 7 high-density regions connected by filaments of galaxies. Nearby superclusters, which are older and more evolved, are much more densely concentrated. In Hyperion, matter is spread out more uniformly as connected blobs of loose associations of galaxies.
Why the difference? Most likely because superclusters have had billions of years for gravity to gather matter together into denser regions — a process that has been acting for far less time in the much younger Hyperion.
The universe is always rife with surprises. How much more don’t we know?