Astronomers have used the James Webb Space Telescope to catch an extraordinary glimpse of a massive galaxy taking shape in the early universe. They identified a compact group of at least six galaxies that are likely to merge into a single enormous system. At the heart of this cosmic construction site lies a growing supermassive black hole.
The international study was led by astronomers at Leiden University and the University of Oxford. The findings have been published in The Open Journal of Astrophysics and Astronomy & Astrophysics.
The system observed, TGSSJ1530+1049, lies more than twelve billion light-years away. We are seeing it as it was when the universe was only about one and a half billion years old. Researchers pointed the James Webb Space Telescope at this location because earlier radio observations had hinted at an active supermassive black hole. The new data revealed that the surrounding region is far more complex than expected. 'We didn't find a single galaxy, but an entire complex of at least six galaxies,' says Aayush Saxena of the University of Oxford.
'We think we are seeing a rare moment when several massive galaxies still exist separately, but are already in the process of forming one much larger galaxy.'
A crucial phase in cosmic evolution
Four of the galaxies already turn out to be surprisingly massive. Together, they contain hundreds of billions of solar masses' worth of stars within a region only a few tens of thousands of light-years across. This makes the system one of the densest known concentrations of massive galaxies from this early period in the universe.
According to co-author Roderik Overzier of Leiden Observatory, the system offers a rare window on a key stage in cosmic evolution. 'We call structures like this protoclusters: the precursors of the vast collections of galaxies we see today. These are places where matter came together very early on. We think we are seeing a rare moment when several massive galaxies still exist separately, but are already in the process of forming one much larger galaxy.'
Central black hole
The team believes that the merging galaxies are linked to the growth of the central black hole. Radio observations provide further clues. 'Using a network of connected radio telescopes, we were able to produce a very sharp image of TGSSJ1530+1049,' says Krisztina Gabányi of Eötvös Loránd University in Budapest. 'The radio emission is produced as material falls into the black hole, while some of it is expelled again at high speed.' The observations suggest that the black hole is still relatively young.
According to co-author Huub Röttgering, the researchers may have caught the system at a pivotal moment. 'What makes this special is that we can follow both the build-up of a giant galaxy and the growth of the black hole at its centre,' he says. The observations therefore offer a rare look at a cosmic construction site in the young universe, where the ancestors of today's largest galaxies are taking shape.
