Free Astronomy Magazine July-August 2018

20 SPACE CHRONICLES Ancient galaxy megamergers by ESO U sing the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder Experi- ment (APEX), two international teams of scien- tists led by Tim Miller from Dalhousie University in Canada and Yale University in the US and Iván Oteo from the University of Edinburgh, United King- dom, have uncovered startlingly dense concen- trations of galaxies that are poised to merge, forming the cores of what will eventually become colossal galaxy clus- ters. Peering 90% of the way across the observable Universe, the Miller team observed a galaxy protocluster named SPT2349-56. The light from this object began travelling to us when the Universe was about a tenth of its cur- rent age. The individual galaxies in this dense cosmic pileup are starburst galax- ies and the concentration of vigorous star formation in such a compact region makes this by far the most active region ever observed in the young Universe. Thousands of stars are born there every year, compared to just one in our own Milky Way. The Oteo team discovered a similar megamerger formed by ten dusty star-forming galaxies, nicknamed a “dusty red core” because of its very red colour, by combining observations from ALMA and the APEX. Iván Oteo explains why these objects are unexpected: “The lifetime of dusty starbursts is thought to be relatively short, because they consume their gas at an extraordinary rate. At any time, in any corner of the Universe, these galaxies are usually in the minority. So, finding numer- JULY-AUGUST 2018