Astronomers have discovered the oldest known pair of closely spaced quasars in the universe, dating back to just 900 million years after the Big Bang. The two actively feeding supermassive black holes are so large that scientists say there is currently no definitive theoretical explanation for how they could have grown to such a size so early in the history of the Universe.
The pair, designated J1602+4228AB, has been given the Hawaiian name Nāpōwawāʻenakaulua. It is the most distant and oldest compact quasar pair ever observed, as well as the third known example from the period known as cosmic dawn.
Discovery and Observations
The discovery was made by an international team of astronomers using the Gemini North telescope in Hawai‘i and the James Webb Space Telescope (JWST). The research was led by Silvia Onorato, a postdoctoral research associate at NSF NOIRLab, with the findings published in The Astrophysical Journal Letters.
Quasars are among the brightest objects in the universe. They form when supermassive black holes at the centres of galaxies draw in vast quantities of gas and stars. As this material falls towards the black holes, some of its mass is converted into energy, producing intense radiation that can outshine the entire galaxy. Astronomers believe pairs of quasars should be relatively common, given how frequently galaxies interact and merge. However, finding them has proved challenging.
Characteristics of the Pair
Their active feeding periods are relatively short, while their enormous distances make them faint and difficult to observe. When two quasars are close together, distinguishing them as separate objects presents an additional challenge. Nāpōwawāʻenakaulua is separated by approximately 18,100 light-years – about a fifth of the diameter of the Milky Way. The two black holes have estimated masses of 1.5 billion and 400 million times that of the Sun respectively.
Their distance means astronomers are observing them as they appeared when the Universe was only 900 million years old, around a thirteenth of its current age. At that stage, the first stars, galaxies and black holes were still relatively young, making the discovery particularly significant for scientists studying how cosmic structures formed.
Significance and Future Research
‘There is no definitive theoretical explanation for how a single one of these giant quasars exists so early in the age of our Universe, much less two,’ says Onorato. ‘We observed Nāpōwawāʻenakaulua at a time when the Universe was only a thirteenth of its age and astonishingly, its supermassive black holes are just as massive as those we see today.’
The discovery was made while researchers were examining data from the Aether survey, a James Webb Space Telescope programme led by Emanuele Paolo Farina, associate scientist at NSF NOIRLab and Gemini. The survey aims to build a census of objects in the early Universe. Using JWST’s Near-Infrared Spectrograph Integral Field Unit, researchers gathered data on 200 quasars, representing 43% of all those known from this period of cosmic history.
During a visual examination of the data, the team noticed that one quasar, J1602+4228A, appeared to have a companion. Follow-up observations using the Gemini North telescope’s Gemini Near-Infrared Spectrograph (GNIRS) enabled researchers to distinguish the two objects. The second quasar, J1602+4228B, is particularly faint, and its close proximity to its companion meant that observing it from the ground was expected to be extremely difficult. However, favourable weather and exceptionally clear skies at Maunakea allowed the team to collect the necessary 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,’ says Onorato.
Further observations using Gemini’s Multi-Object Spectrograph helped researchers establish the properties of the pair. The name Nāpōwawāʻenakaulua was created through the A Hua He Inoa programme at the ʻImiloa Astronomy Center of Hawaiʻi, in collaboration with the University of Hawai‘i’s Hawaiian Language College, Ka Haka ʻUla O Keʻelikōlani. It translates as ‘Two celestial bodies of fathomless powerful darkness in the brilliance of heat reincarnating energy into the Universe’.
Although the origins of the pair remain uncertain, the researchers believe it could point to an unusually dense region of matter in the early Universe. Such an environment may have encouraged galaxies to interact frequently, simultaneously fuelling the formation of stars and the rapid growth of their central black holes.
‘Nāpōwawāʻenakaulua is a really unique environment,’ says Onorato. ‘It’s a laboratory for astronomers to study how the very first massive galaxies and their central black holes assembled together through direct galaxy interactions during these early times.’
