Vast Galactic Megamerger In the Early Universe Is 'Truly Unique' Discovery

An international team of astronomers has spotted a vast cosmic pileup of ancient galaxies at a time when the universe was just a tenth of its current age.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX), the scientists discovered an extremely dense concentration of young galaxies that are about to merge and form a galaxy cluster—the largest structure in the known universe.

Astronomers previously thought these events only occurred around 3 billion years after the Big Bang, so they were surprised to find that this merger was happening when the universe was only half that age.

"This is a truly unique object, originating back to when the universe was only 1 billion years old," Carlos de Breuck, one of the authors of a new Nature study describing the findings, told Newsweek.

The galactic pileup, or proto-cluster, is known as SPT2349-56 and lies 90 percent of the way across the observable universe. Because the light from it takes billions of years to reach us, scientists are essentially looking back in time when they observe it.

The individual galaxies in this megamerger are known as starburst galaxies—galaxies that are undergoing exceptionally high rates of star formation. In fact, scientists found that this region was the most active ever observed in the young universe.

"In our neighborhood [the Milky Way], we see that about one star gets formed per year," De Breuck said. "In SPT2349-56, there are at least 7,000 such stars formed per year, and maybe as many as 15,000. So the sky would look much brighter if we were living on a planet in the SPT2349-56 cluster."

This artist's impression of SPT2349-56 shows a group of interacting and merging galaxies in the early uUniverse. Such mergers have been spotted using the ALMA and APEX telescopes and represent the formation of galaxies clusters, the most massive objects in the modern universe. ESO/M. Kornmesser

Current theoretical and computer models had suggested that proto-clusters as massive as this should have taken much longer to evolve.

"How this assembly of galaxies got so big so fast is a mystery," Tim Miller, a Ph.D. candidate at Yale University and lead author of the paper, said in a statement. "It wasn't built up gradually over billions of years, as astronomers might expect. This discovery provides a great opportunity to study how massive galaxies came together to build enormous galaxy clusters."