Galaxies grow and evolve by merging with other galaxies, shuffling their billions of stars, causing energetic bursts of star formation, and often feeding central supermassive black holes to create bright quasars that outshine the entire galaxy. Some of these mergers eventually become large elliptical galaxies containing black holes billions of times the mass of our Sun. While astronomers have observed a true galaxy merger with multiple quasars in our own cosmic neighbourhood, more distant examples where the universe is only a quarter of its current age are extremely rare and extremely difficult to find.

Using a number of ground-based and space-based observatories, including Gemini North, half of NSF’s Gemini International Observatory operated by NOIRLab, a team of astronomers has discovered a pair of closely related supermassive black holes — actively feeding quasars. The discovery is the first confirmed detection of a double supermassive black hole in the same galactic “cosmic noon,” a frenetic star-forming period when the universe was only three billion years old.

Previous observations had found similar systems in the early stages of merging, when the two galaxies could still be considered distinctly separate entities. But these new results show that the quasar pair exploded so close together, only 10,000 light-years from each other, that their parent galaxy is likely on its way to becoming a single giant elliptical galaxy.

Finding pairs of supermassive black holes so close together at this early age is like trying to find the famous needle in a haystack. The problem is, most black hole pairs are too close to tell them apart. To definitively detect such a system, two supermassive black holes would need to be actively accumulating and glowing like quasars at the same time, which is extremely rare conditions. According to statistics, for every 100 supermassive black holes, only one needs to be actively accumulating at any given time.

However, astronomers know that the distant universe must be full of supermassive black hole pairs embedded in merging galaxies. The first clues to such a system were found in data from the NASA/ESA Hubble Space Telescope, which revealed two close points of light in the distant universe.

To test the true nature of this system, the team searched the extensive database of ESA’s Gaia observatory and found that the system had a distinct “wobble” that could be the result of erratic changes in the black hole’s feeding activity.