It’s an amazing discovery but scientists do not know yet how to explain it. Thanks to the ALMA and APEX telescopes, two scientific teams, one American and one British, have discovered very dense concentrations of galaxies about to merge to form the nuclei of gigantic clusters. If these phenomena are not in themselves very surprising, it is the period in which they occurred that leaves astronomers wondering. Indeed, light from these objects was emitted when the Universe was only one tenth of its current age, only 1.5 billion years after the big bang. But scientists thought so far that this type of event occurred much later, around 3 billion years after the big bang.
The American team, led by Tim Miller of Dalhousie University in Canada and Yale University, identified a proto-cluster of 14 massive galaxies, all of them star making galaxies, which the team christened SPT2349-56. The British team led by Ivan Oteo of the University of Edinburgh, had for its part uncovered a similar cluster of 10 dusty star-forming galaxies, dubbed “dusty red nucleus” because of its pronounced red color .
“These discoveries from ALMA are just the tip of the iceberg. Additional observations using the APEX telescope show that the actual number of star-forming galaxies is likely to be three times higher. Another observation campaign currently being carried out with the MUSE instrument, installed on the ESO’s VLT, is also leading to the identification of other galaxies “, notes Carlos De Breuck, ESO astronomer, in a statement.
On the composite image above are three views of a distant set of galaxies interacting and merging with each other within the Young Universe. The left side image consists of a wide field view acquired by the South Pole Telescope (SPT). It shows a unique bright point. The central image, acquired by the Atacama Pathfinder Experiment (APEX), reveals more details. Finally, the right lateral image is from the Atacama Large Millimeter / submillimeter Array (ALMA). It highlights the existence of 14 galaxies about to fuse to form a galactic cluster.
However, Ivan Oteo explains that these objects are supposed to be rare. “The lifespan of dusty stellar bursts is considered relatively short because they consume their gas at an extraordinarily high rate. At any moment, and in every point of the universe, these galaxies are generally in the minority. Discovering many dusty stellar jumps at the same time is therefore particularly confusing. It is a reality that remains to be understood. As for the current theoretical and computer models, they predict that the time required for the evolution of proto-masses as massive is longer than these observations suggest.”
The process responsible for the rapid aggregation of so many galaxies remains a mystery. This cluster has not built up gradually over billions of years, contrary to what astronomers thought. “This discovery provides a great opportunity to study how massive galaxies have come together to form gigantic galactic clusters,” concludes Tim Miller.