A newly discovered conglomeration of galaxies, or supercluster, dating just 2.3 billion years after the Big Bang, is the largest object ever found from so early in the universe. The structure's mass is almost 5,000,000,000,000,000 times that of the Sun, or almost 10,000 times our entire galaxy. The astronomers who found it named it Hyperion, after the titan of Greek mythology who fathered the Sun (and also has a moon of Saturn named after him)
Superclusters are the largest structures in the universe; assemblies of galaxies hundreds of millions of light-years across. Their existence demonstrates the early universe was somewhat lumpy, rather than being made from evenly distributed matter.
Galactic superclusters of similar size to Hyperion have been found, but astronomers were surprised to find something so large had formed so soon after the universe began. "Normally these kinds of structures are known at lower redshifts, which means when the Universe has had much more time to evolve and construct such huge things,” said Dr Olga Cucciati of the University of Bologna in a statement.
Being so much younger, Hyperion lacks the development of superclusters of similar size. Compared to these “The mass is distributed much more uniformly in a series of connected blobs, populated by loose associations of galaxies,” said University of California astronomer Dr Brian Lemaux, another of the authors of a forthcoming paper in Astronomy and Astrophysics (preprint available to read on arXiv.org) describing the discovery.
Despite being smoother than its later counterparts, Hyperion has a more complex structure than astronomers expected given its age. They have counted seven high-density regions within it, with filaments of galaxies stretching between them. Cucciati, Lemaux, and co-authors have estimated the mass of the individual dense regions, with the largest around 2.7 x 1014 solar masses.
Hyperion provides us with a snapshot of the way supercluster structure develops, and raises hope we will find further examples, both earlier and later in the process.
The titanic structure was found using a giant of a different sort, the European Southern Observatory's Very Large Telescope, which can combine up to three mirrors, each 8.2 meters (27 feet) across, to operate as if they were a single telescope. The discovery was made in the course of the Ultra-Deep Survey of a part of the constellation Sextans, which is producing a three-dimensional map of more than 10,000 galaxies from the early universe.
Previous mapping of the area had identified the presence of an enormous number of galaxies in the high-density regions. However, the fact that they were all united into one of the largest structures in the universe, on its way to becoming a supercluster, had not previously not been recognized.