An international team of astronomers has identified a distant quasar, known as ID830, as the most X-ray luminous radio-loud quasar to date. This groundbreaking discovery emerged from observations made using the Spektr-RG spacecraft alongside various ground-based telescopes. The findings were published on November 7, 2025, on the pre-print server arXiv.
Quasars, or quasi-stellar objects (QSOs), are active galactic nuclei powered by supermassive black holes (SMBHs). They exhibit extraordinarily high bolometric luminosities, exceeding one quattuordecillion erg/s, and emit electromagnetic radiation across radio, infrared, visible, ultraviolet, and X-ray wavelengths. ID830, designated as eFEDS J084222.9+0010000, has a redshift of 3.43 and reaches a bolometric luminosity of approximately one quindecillion erg/s. This suggests that it contains either an exceptionally massive SMBH nearing the limit of 10 billion solar masses or is undergoing super-Eddington accretion.
Led by Sakiko Obuchi from Waseda University in Tokyo, Japan, the astronomers conducted a multiwavelength study to explore the nature of ID830. They combined data from eROSITA X-ray spectroscopy, the Sloan Digital Sky Survey (SDSS), and Subaru/MOIRCS rest-frame ultraviolet–optical spectra, along with extensive radio data from LOFAR, GMRT, FIRST, ASKAP, and VLASS.
The research revealed that ID830 exhibits an X-ray luminosity of 0.01 quindecillion erg/s, establishing it as one of the most X-ray luminous radio-loud quasars observed thus far. Its bolometric luminosity was measured at around 0.076 quindecillion erg/s, yielding an Eddington ratio of 1.4, which confirms the occurrence of super-Eddington accretion.
Notably, ID830 showed moderate reddening of approximately 0.39 mag, and the mass of its supermassive black hole was estimated at about 440 million solar masses. The quasar also demonstrated a high ratio of ultraviolet-to-X-ray luminosities, calculated to be -1.2, which is higher than that of other quasars and “little red dots” (LRDs) in the super-Eddington phase with similar ultraviolet luminosities. LRDs are thought to represent a type of early AGN with SMBHs.
The study indicates that the estimated jet kinetic power of ID830 ranges from 1 to 10 quattuordecillion erg/s, comparable to its radiative luminosity. This suggests that the mechanical energy from the jet efficiently couples with the host interstellar medium, enhancing our understanding of the quasar’s environment.
The authors of the study conclude that ID830 is in a transitional phase where both the corona and jet are energized following an accretion burst. They posit that ID830 may serve as a bridge between sub-Eddington quasars and X-ray weak, rapidly accreting “little red dots” recently identified by the James Webb Space Telescope (JWST).
This significant research contributes to the broader understanding of quasars and their evolution, shedding light on the behavior of supermassive black holes and their impact on the surrounding cosmos.
