An international team of astronomers led by researchers from Waseda University and Tohoku University has identified an unusual quasar in the early Universe that contains one of the fastest-growing supermassive black holes known for its size. Data from the Subaru Telescope show a surprising mix of traits. The quasar is pulling in matter at an exceptionally high rate while also emitting intense X-rays and launching a strong radio jet. Many existing theories suggest these features should not appear together, making this object a rare and revealing find. The observations provide fresh insight into how supermassive black holes may have grown so quickly in the Universe’s early days.
Supermassive black holes, with masses ranging from millions to billions of times that of the Sun, reside at the centers of most galaxies. They increase in size by drawing in surrounding gas. As this material spirals inward, it forms a rotating accretion disk and can energize a compact region of extremely hot plasma known as a corona (a key source of X-rays). In some cases, the system also produces a narrow jet that shines brightly at radio wavelengths. When black holes are actively feeding and extremely luminous, they are known as quasars. A major unanswered question remains how some of these giants became so massive so early in cosmic history.
Pushing Beyond the Black Hole Growth Limit
One proposed explanation for rapid early growth is super-Eddington accretion. Under standard conditions, radiation released by infalling material pushes outward, limiting how fast a black hole can grow. This theoretical cap is known as the Eddington limit. Certain extreme environments, however, may allow black holes to exceed this limit for short periods, leading to very rapid increases in mass.
To investigate whether this kind of growth occurred in the early Universe, the researchers used the Subaru Telescope’s near-infrared spectrograph (MOIRCS). By tracking the motion of gas near the quasar and analyzing the Mg II (2800 Å) emission line, they estimated the black hole’s mass. The results point to a supermassive black hole that existed about 12 billion years ago and is accreting matter at roughly 13 times the Eddington limit, based on X-ray measurements.
A Quasar That Defies Expectations
What sets this object apart is how it behaves across different wavelengths of light. Many theoretical models predict that during super-Eddington growth, changes in the inner structure of the accretion flow should weaken X-ray emission and suppress jet activity. Instead, this quasar remains bright in X-rays and strongly radio-loud at the same time. The findings suggest the black hole is growing at an extreme pace while still maintaining an active corona and a powerful jet. This unusual combination points to physical processes that current models do not yet fully explain.
The team suggests the quasar may be observed during a short transitional period, possibly following a sudden influx of gas. In this scenario, a rapid increase in available material drives the black hole into a super-Eddington state. For a limited time, both the X-ray-emitting corona and the radio jet remain highly energized before the system gradually settles into a more typical mode of growth.
If this interpretation is correct, the object offers a rare chance to study black hole growth as it changes over time in the early Universe, an important step toward explaining how supermassive black holes formed so rapidly.
Implications for Galaxy Evolution
The strong radio signal indicates that the jet carries enough energy to affect its surroundings. Such jets can heat or disrupt gas within the host galaxy, potentially influencing star formation and shaping how galaxies and their central black holes evolve together. The relationship between super-Eddington growth and jet-driven feedback is still not well understood, and this quasar provides a valuable reference point for testing new ideas.
Lead author Sakiko Obuchi (Waseda University) says:
“This discovery may bring us closer to understanding how supermassive black holes formed so quickly in the early Universe. We want to investigate what powers the unusually strong X-ray and radio emissions, and whether similar objects have been hiding in survey data.”
The findings were published as Obuchi et al. “Discovery of an X-ray Luminous Radio-Loud Quasar at z = 3.4: A Possible Transitional Super-Eddington Phase” in the Astrophysical Journal on January 21, 2026.
The research was supported by Grants-in-Aid for Scientific Research (Grant Nos. 25K01043, 23K13154, 22H00157), the JST FOREST Program (JPMJFR2466), and a research grant from the Inamori Foundation.
The Subaru Telescope is a large optical-infrared observatory operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences, with support from the MEXT Project to Promote Large Scientific Frontiers. The team acknowledges and respects the cultural, historical, and natural significance of Maunakea in Hawai`i, from where these observations were made.
