An international team of astronomers has identified a distant quasar, designated as ID830, as the most X-ray luminous radio-loud quasar known to date. This significant discovery was facilitated by observations from the Spektr-RG spacecraft and various ground-based telescopes. The findings were published on November 7, 2025, on the pre-print server arXiv.
Located at a redshift of 3.43, ID830 reaches an extraordinary bolometric luminosity of approximately one quindecillion erg/s. This suggests the presence of either an exceptionally massive supermassive black hole (SMBH) nearing the maximum mass limit of 10 billion solar masses or an SMBH undergoing a super-Eddington accretion phase. A research team led by Sakiko Obuchi from Waseda University in Tokyo, Japan, set out to explore ID830’s characteristics through a comprehensive multiwavelength study.
By integrating data from various sources, including eROSITA X-ray spectroscopy and extensive radio data from facilities such as LOFAR, GMRT, and ASKAP, the researchers revealed that ID830 exemplifies a rare type of quasar with an extreme X-ray excess. The study determined that ID830 has an X-ray luminosity of approximately 0.01 quindecillion erg/s, marking it as one of the most luminous radio-loud quasars detected to date.
The researchers reported that ID830’s bolometric luminosity is about 0.076 quindecillion erg/s, yielding an Eddington ratio of 1.4. This ratio confirms that ID830 is experiencing super-Eddington accretion. Furthermore, the quasar exhibits a moderate reddening of around 0.39 mag, and the mass of its central black hole is estimated to be around 440 million solar masses.
ID830 also displays a high ratio of ultraviolet-to-X-ray luminosities, calculated at -1.2. This ratio is greater than that of other quasars and early active galactic nuclei (AGNs) referred to as “little red dots” (LRDs) in a similar phase. The study estimates that ID830’s jet kinetic power ranges from 1 to 10 quattuordecillion erg/s, comparable to its radiative luminosity, indicating an efficient coupling of mechanical energy from the jet to the host galaxy’s interstellar medium.
The findings suggest that ID830 is in a transitional phase, where the corona and jet are both energized following an accretion burst. The authors assert that ID830 may represent a post-burst super-Eddington quasar that bridges the gap between sub-Eddington quasars and the recently identified X-ray weak, rapidly accreting “little red dots” detected by the James Webb Space Telescope (JWST).
This research sheds light on the complexities of quasar behavior and the nature of supermassive black holes, contributing to our understanding of the universe’s most luminous objects. The collaborative efforts of this international team highlight the significance of multiwavelength observations in advancing astronomical knowledge.
