Earliest Known Compact Quasar Pair Defies Models of Early Black Hole Growth

Two black holes, feeding hard and shining brighter than the galaxies around them, are sitting about 18,100 light-years apart. That is roughly a fifth the width of the Milky Way. We see them as they were only 900 million years after the Big Bang. Astronomers have now confirmed that this is the oldest compact quasar pair ever observed, and that no established theory explains how it got there.

The pair is catalogued as J1602+4228AB. It also carries a Hawaiian name, Nāpōwawāʻenakaulua. The name was created through the A Hua He Inoa program at the ʻImiloa Astronomy Center of Hawaiʻi and the University of Hawaiʻi's Ka Haka ʻUla O Keʻelikōlani, the Hawaiian Language College. It translates to "Two celestial bodies of fathomless powerful darkness in the brilliance of heat reincarnating energy into the universe." The pair is the most distant compact quasar pair known, and the most compact found in the era called cosmic dawn. It is only the third known quasar pair from that period.

A quasar is a supermassive black hole at the center of a galaxy that is pulling in gas and stars. Some of that infalling matter is converted to energy, and the black hole becomes bright enough to outshine every star in its host galaxy. Galaxy mergers were common in the early universe, so astronomers expect many close quasar pairs. Finding them is hard for three reasons. A black hole's quasar phase is relatively short. The objects are far away and faint, which makes them difficult to detect from the ground. And at such small separations, the two members of a pair are difficult to tell apart.

The masses are what unsettle the models. The two black holes weigh about 1.5 billion and 400 million times the mass of the sun. In the first billion years, the first stars, galaxies and black holes were still young. Silvia Onorato, a postdoctoral research associate at NSF NOIRLab who led the study, said there is no definitive theoretical explanation for how even one such giant quasar exists so early, much less two. She noted that the universe was only a thirteenth of its present age, yet these black holes are as massive as those seen today.

The discovery came out of the Aether survey, a James Webb Space Telescope program led by Emanuele Paolo Farina, an associate scientist at NSF NOIRLab/Gemini. Aether aims to build a census of objects in the early universe. Using JWST's Near-Infrared Spectrograph Integral Field Unit, it collected a sample of 200 quasars, which is 43 percent of all known quasars at this stage of cosmic history. During visual inspection of that data, the team noticed that quasar J1602+4228A had a companion.

To separate the two, they turned to the Gemini North telescope on Maunakea in Hawaiʻi and its Gemini Near-Infrared Spectrograph, GNIRS. The companion, J1602+4228B, is so close to A and so faint that observing it from the ground should have been nearly impossible. Good timing and excellent weather made it possible. Onorato said the sky was so clean and sharp that the data were gathered in just two nights. Further observations with the Gemini Multi-Object Spectrograph, GMOS, narrowed down the properties of the pair.

The full origin of the system remains unexplained. The team proposes that the pair may mark an extreme peak in the matter density of the early universe, a place where galaxy interactions drove star formation and rapid black hole growth at the same time. Onorato called it a laboratory for studying how the first massive galaxies and their central black holes assembled through direct interactions. The results appear in The Astrophysical Journal Letters, and the open question is whether theory can be made to account for them.