Scientists may need to rewrite the text books after discovering a cluster of galaxies that formed in the early universe that look more mature than they should.
The cluster, named CL J1449+0856, is a grouping of galaxies gravitationally bound together into a single massive structure.
Its discovery means mature galaxy clusters were already in place 10.7 billion years ago, when the universe was a quarter of its current age.
Although more distant clusters have been seen before, they all appeared young and still forming.
Reporting in the journal Astronomy and Astrophysics, lead researcher Raphael Gobat from the Commissariat a l'Energie Atomique (CEA) in France, says galaxy clusters are difficult to study because they're scarce, especially in the early universe.
"This is why discovering a galaxy cluster at a redshift of 2.07 feels like unearthing a rare and valuable gem," says Gobat. Redshift is a measure of the change in frequency in light waves coming from an object that is moving away from the observer.
"As well as being at a record-breaking distance, what makes this unique is that it's not a proto-cluster undergoing formation, but an already mature, proper galaxy cluster."
According to the researchers, the chance discovery of CL J1449+0856 occurred during analysis of infrared data from NASA's Spitzer Space Telescope.
"The structure caught our eyes as a clump of galaxies which appeared much redder and more concertrated than those in the surroundings," says co-author Emmanuele Daddi, also of CEA.
Using the Very Large Telescope in Chile the astronomers determined how far away the cluster was. Hubble Space Telescope images showed most of the galaxies in the cluster won't forming new stars and were dominated by cool red stars more than a billion years old.
Using ESA's XMM-Newton telescope, researchers detected x-ray emissions caused by gas compressed and heated by the cluster's gravity to over 10 million degrees Celsius - something only older galactic clusters do.
The findings were later confirmed by a number of ground and space-based telescopes.
Professor Andrew Hopkins from the Australian Astronomical Observatory says the discovery raises concerns about accepted theories on cosmic structure formation.
"It's actually been known for some time that this model has difficulty in reproducing observations," says Hopkins.
This result really hammers home that inconsistency between our best understanding of how we think structures form and what we observe.
Hopkins says simulations based on current models indicate galactic clusters as massive and mature as this one do form, but much later in the evolution of the universe.
"But this discovery shows clusters form much faster."