An international team of astronomers has identified ID830 as the most X-ray luminous radio-loud quasar to date. This discovery, made using the Spektr-RG spacecraft and various ground-based telescopes, was published on November 7, 2025, on the pre-print server arXiv. Quasars, or quasi-stellar objects, are powered by supermassive black holes and exhibit extraordinary luminosities across multiple wavelengths, including radio and X-ray.
The quasar ID830, located at a redshift of 3.43, demonstrates a bolometric luminosity of approximately one quindecillion erg/s. This remarkable figure suggests that ID830 either contains a supermassive black hole nearing the upper mass limit of 10 billion solar masses or is in a super-Eddington accretion phase. Researchers led by Sakiko Obuchi from Waseda University in Tokyo, Japan, aimed to explore these possibilities through a comprehensive multiwavelength study.
Significant Findings from Multiwavelength Observations
The team utilized a combination of eROSITA X-ray spectroscopy, SDSS, and Subaru/MOIRCS rest-frame ultraviolet-optical spectra, along with extensive radio data from instruments such as LOFAR, GMRT, FIRST, ASKAP, and VLASS. Their findings indicate that ID830 is a rare example of a super-Eddington, radio-loud quasar, characterized by an extreme X-ray excess.
The study revealed that ID830 possesses an X-ray luminosity of 0.01 quindecillion erg/s, positioning it among the most luminous radio-loud quasars detected so far. Its bolometric luminosity was measured at approximately 0.076 quindecillion erg/s, resulting in an Eddington ratio of 1.4, which confirms the presence of super-Eddington accretion. The quasar also exhibits moderate reddening of about 0.39 mag and is estimated to host a supermassive black hole with a mass of around 440 million solar masses.
Moreover, ID830 showcases a high ultraviolet-to-X-ray luminosity ratio of -1.2, which is notably greater than that of other quasars and little red dots (LRDs) in the super-Eddington phase. LRDs are believed to be early active galactic nuclei with supermassive black holes.
A Transitional Phase for ID830
The research team highlights that the results suggest ID830 is in a transitional phase, where the corona and jet are concurrently energized following an accretion burst. According to the authors, “ID830 may represent a post-burst super-Eddington quasar bridging the gap between sub-Eddington quasars and the X-ray weak, rapidly accreting ‘little red dots’ recently identified with JWST.”
The estimated jet kinetic power of ID830 ranges from 1 to 10 quattuordecillion erg/s, which is comparable to its radiative luminosity. This indicates that the mechanical energy generated by the jet can effectively interact with the host’s interstellar medium.
The findings from this study not only advance the understanding of quasars but also open new avenues for research into the characteristics and behaviors of supermassive black holes across the universe. The implications of ID830’s unique properties could reshape existing models of quasar evolution and activity.
This article relies on the rigorous editorial process and fact-checking conducted by the team at Science X. For further details on this research, refer to the publication by Sakiko Obuchi et al, titled “Discovery of an X-ray Luminous Radio-Loud Quasar at z=3.4: A Possible Transitional Super-Eddington Phase,” available on arXiv (DOI: 10.48550/arxiv.2511.05029).
