Free Astronomy Magazine July-August 2023

41 JULY-AUGUST 2023 in the early stages of merging, when the two galaxies could still be con- sidered clearly separate entities. But these new results show a pair of quasars blazing away in such close proximity, a mere 10,000 light-years apart, that their original host galax- ies are likely well on their way to be- coming a single giant elliptical gal- axy. Searching for pairs of supermas- sive black holes so close to each other during this early epoch is like Astronomers know, however, that the distant Universe should be brimming with pairs of supermassive black holes embedded within merging galaxies. The first hints of such a system were found in data from the NASA/ESA Hubble Space Telescope, which re- vealed two closely aligned pinpoints of light in the distant Universe. To verify the true nature of this system, the team searched through ESA’s Gaia observatory’s vast database and found that this system had an appar- ent “jiggle,” which could be the re- sult of sporadic changes in a black hole's feeding activity. The team then used the Gemini Multi-Object Spec- trograph (GMOS) and the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, which provided the team with independent measure- ments of the distance to the quasars and confirmed that the two objects were both quasars rather than a chance alignment of a single quasar with a foreground star. Further stud- ies with the W.M. Keck Observatory, NSF’s Karl G. Jansky Very Large Array, and NASA’s Chandra X-ray Observa- tory also helped to confirm these ob- servations. “The confirmation process wasn’t easy and we needed an array of telescopes covering the spectrum from X-rays to the radio to finally confirm that this system is indeed a pair of quasars, instead of, say, two images of a gravitationally lensed quasar,” said co-author Yue Shen, an astronomer at the University of Illi- nois. “We don't see a lot of double quasars at this early time. And that's why this discovery is so exciting. Knowing about the progenitor pop- ulation of black holes will eventually tell us about the emergence of super- massive black holes in the early Uni- verse, and how frequent those merg- ers could be,” said graduate student Yu-Ching Chen of the University of Illinois at Urbana-Champaign, lead author of this study, which is pub- lished in the journal Nature . ! T his artist's impression illus- trates that astronomers using an array of ground- and space-based telescopes, including Gemini North on Hawai‘i, have uncovered a closely bound duo of energetic quasars — the hall- mark of a pair of merging galax- ies — seen when the Universe was only three billion years old. This discovery sheds light on the evolution of galaxies at “cosmic noon,” a period in the history of the Universe when galaxies un- derwent bursts of furious star formation. [International Gemini Observatory/NOIRLab/NSF/AURA/ M. Zamani, J. da Silva] trying to find the proverbial needle in a haystack. The challenge is that most black-hole pairs are too close to distinguish individually. To defin- itively detect such a system, the two supermassive black holes need to be actively accreting and shining as quasars simultaneously, conditions that are extremely rare. Statistically, for every 100 supermassive black holes only one should be actively ac- creting at a given time.