Quasars are among the brightest beacons in the Universe, powered by supermassive black holes that swallow gas at their centers. Although they shine across billions of light-years, their extreme distances and tiny sizes make it very difficult to see what is happening in the immediate surroundings of the black hole itself. Now, for the first time, an international team of astronomers, including at PKU, have managed to directly resolve the inner structure of a quasar at redshift 4—when the Universe was less than 1.5 billion years old—opening a new window into how black holes grew in the early cosmos.
This breakthrough was made possible by the newly upgraded adaptive optics system at the Very Large Telescope Interferometer, developed by the Max Planck Institute for Extraterrestrial Physics (MPE) and the GRAVITY+ consortium. The system, adapted from technology used in the ERIS instrument, allows much sharper and deeper views of the distant Universe. With this capability, astronomers targeted the most luminous known quasar at redshift 4, more than 12 billion light-years away, and directly resolved its broad-line region—the fast-moving gas close to the central black hole. By combining GRAVITY+ interferometric data with spectra from ERIS, they built a detailed model of the gas motions and discovered that, despite the quasar’s dazzling luminosity, its black hole weighs only about 800 million solar masses—nearly 10 times smaller than traditional methods would suggest.
Even more surprising, the data reveal that most of the gas in the broad-line region is not rotating but rushing outward at tremendous speeds, up to 10,000 km/s. “The outflow in the broad-line region has long been inferred indirectly from the shape of emission-line profiles,” said Prof. Luis C. Ho, Director of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University and co-author on the study. “What is remarkable here is that we have, for the first time, spatially resolved the outflow structure at its launching site. This opens a new window on how black hole accretion drives feedback, shaping the growth of galaxies in the early Universe.”
To interpret the interferometric signal, Prof. Jinyi Shangguan, one of the corresponding authors, at KIAA developed a new model for an outflowing broad-line region that was essential for disentangling the complex gas motions. “We used this extreme quasar as a testbed for our outflowing broad-line region model,” said Shangguan. “Properly accounting for broad-line region outflows will be crucial for understanding the general physics of active galactic nuclei, especially with the large samples we expect from GRAVITY+ starting in 2026. This work is a strong beginning for our Max Planck Partner Group, and we look forward to pushing the boundaries of what interferometric observations can achieve.”
For this study, Prof. Shangguan developed the new broad-line region model and contributed to the data analysis, while Prof. Ho and Dr. Ruancun Li, recent PhD student of KIAA and soon to join MPE as a postdoc, contributed to the interpretation of the quasar and its gas dynamics. Building on KIAA’s long-standing expertise in quasar research, this collaboration lays a solid foundation for future joint efforts with MPE and the GRAVITY team.
Original publication
Spatially resolved broad line region in a quasar at z=4 – Dynamical black hole mass and prominent outflowGRAVITY+ Collaboration
Link: https://arxiv.org/abs/2509.13911
Submitted to A&A
Images
https://noirlab.edu/public/images/noirlab2427d/
This artist’s illustration shows a rapidly feeding black hole that is emitting powerful gas outflows.
Credit: NOIRLab/NSF/AURA/J. da Silva/M. Zamani
Figure 2 with explanation
The best-fit model of the broad-line region overlaid with a schematic explaining the geometry. We see the broad-line region of the galaxy edge-on. The blue part is the prominent outflow directed towards us; the red part is the reverse outflow, which is almost completely hidden from sight.
Credit: MPE, GRAVITY+
Related news:
https://www.mpe.mpg.de/8095572/news20250917
https://www.mpe.mpg.de/7990698/news20240129?c=255802
ERIS, see https://www.mpe.mpg.de/7912661/news20221123?c=255802
AO for GRAVITY – News
