Astronomers have found the most distant, and therefore oldest, compact pair of quasars known. The object, J1602+4228AB, has been given the Hawaiian nickname Nāpōwawāʻenakaulua. We see it as it was just 900 million years after the Big Bang, in the era known as cosmic dawn.
An international team led by Silvia Onorato, a postdoctoral research associate at NSF NOIRLab, made the discovery. The data came from the James Webb Space Telescope (JWST) and the Gemini North telescope on the dormant volcano Maunakea in Hawai‘i. The results are published in the peer-reviewed journal The Astrophysical Journal Letters.
What a quasar pair is
A quasar is a supermassive black hole at the center of a galaxy that is actively feeding. Part of the infalling mass is converted into energy. That makes the black hole shine brighter than all the stars in its host galaxy combined.
In the early Universe, galaxies often interacted, collided and merged. During such events their central black holes received large amounts of gas and stars. Astronomers therefore expect to find many quasar pairs separated by less than the typical size of a galaxy.
Finding them is hard for three reasons. A black hole's quasar phase is relatively short. The objects are very distant, so they are faint and difficult to detect from the ground. And at such small separations, the individual members of a pair are hard to resolve.
How the pair was found
The object turned up in data from the Aether survey. This JWST program is led by Emanuele Paolo Farina of NSF NOIRLab/Gemini and aims to compile a census of objects in the early Universe. Using the Near-Infrared Spectrograph Integral Field Unit (NIRSpec IFU), the survey collected a sample of 200 quasars. That is 43% of all known quasars from this stage of cosmic history.
During visual inspection of the data, the team noticed that quasar J1602+4228A had a companion. Follow-up observations with the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North then resolved the two quasars as individual objects. Component B is very faint and sits very close to A, so observing it from the ground should have been nearly impossible. Good timing and perfect weather on Maunakea let the team collect the data in just two nights.
The sky over Maunakea was so clean and sharp that we managed to collect the data in only two nights.Silvia Onorato, NSF NOIRLab
What's new
Nāpōwawāʻenakaulua is only the third quasar pair known from cosmic dawn. It is also the most compact pair found in this era. The two members are separated by about 18,100 light-years, roughly one-fifth of the Milky Way's diameter.
The black holes have masses of 1.5 billion and 400 million times that of the Sun. That is a great deal for a Universe only 900 million years old, when the first stars, galaxies and black holes were still relatively young.
According to Onorato, the Universe was then only a thirteenth of its current age, yet these black holes are as massive as those we see today. There is no definitive theoretical explanation for how even a single such quasar could exist so early, let alone two. The object therefore challenges current understanding of how large-scale cosmic structures form.
How solid is the result
The main caveat concerns gravitational lensing. A lens is a massive object in front of a light source that distorts its light and can create the false appearance of a second, fainter source. To test this, the team used the Gemini Multi-Object Spectrograph (GMOS) on Gemini North.
The spectra of the two quasars differ in shape. This leads the team to favor a real physical pair. Still, only a lens model can definitively rule out lensing, and such a model is still needed.
The full origin story of the pair also remains unknown. The team proposes that such a pair may be a signpost of an extreme peak in the matter density field of the early Universe. In such a place, galactic interactions would simultaneously have fed star formation and rapid black hole growth.
What the name means
The name was created by the A Hua He Inoa program at the ʻImiloa Astronomy Center of Hawaiʻi and the University of Hawai‘i's Hawaiian Language College. Its author is professor Larry Kimura. It translates as "Two celestial bodies of fathomless powerful darkness in the brilliance of heat reincarnating energy into the Universe."
The name has several parts. Pō means fathomless darkness, standing for the black holes. ʻEna is the brilliance of heat from matter falling onto them. Kaulua means a pair. It also echoes two earlier names from the program: Pōwehi, the first image of a black hole in 2019, and Pōniuāʻena, the most distant quasar known at the time, found in 2020.
What's next
Onorato calls Nāpōwawāʻenakaulua a laboratory for studying how the very first massive galaxies and their central black holes assembled together through direct galaxy interactions. The next likely step is a lens model that confirms or rules out the physical nature of the pair.
