An international collaboration of astronomers has announced that the distant quasar known as ID830 is the most X-ray luminous radio-loud quasar identified to date. This finding, based on observations from the Spektr-RG spacecraft and various ground-based telescopes, was published on November 7, 2025, on the preprint server arXiv.
Quasars, or quasi-stellar objects, are active galactic nuclei powered by supermassive black holes (SMBHs). They exhibit exceptionally high bolometric luminosities, often exceeding one quattuordecillion erg/s. ID830 stands out with a bolometric luminosity of approximately one quindecillion erg/s, suggesting the presence of either an extremely massive SMBH nearing the upper mass limit of 10 billion solar masses or an SMBH undergoing a super-Eddington accretion phase.
### Insights from Multiwavelength Observations
A team led by Sakiko Obuchi from Waseda University in Tokyo undertook a comprehensive multiwavelength study of ID830. The researchers utilized data from eROSITA X-ray spectroscopy, along with ultraviolet-optical spectra from the Sloan Digital Sky Survey (SDSS) and the Subaru/MOIRCS, alongside extensive radio data from observatories such as LOFAR, GMRT, FIRST, ASKAP, and VLASS.
The study revealed that ID830 demonstrates an extraordinary X-ray luminosity of 0.01 quindecillion erg/s, solidifying its status as one of the most luminous radio-loud quasars known. Its bolometric luminosity of approximately 0.076 quindecillion erg/s corresponds to an Eddington ratio of 1.4, confirming the theory of super-Eddington accretion.
### Unique Characteristics of ID830
ID830 exhibits moderate reddening of about 0.39 mag and an estimated mass of the supermassive black hole at about 440 million solar masses. Notably, the quasar has a high ratio of ultraviolet-to-X-ray luminosities, calculated to be -1.2, which is significantly higher than that of other quasars and little red dots (LRDs) in a similar super-Eddington phase. LRDs are believed to represent early AGNs with SMBHs.
The estimated jet kinetic power of ID830 ranges between 1 and 10 quattuordecillion erg/s, which is comparable to its radiative luminosity. This suggests a strong interaction between the mechanical energy from the jet and the host interstellar medium.
### Understanding the Transitional Phase
The findings indicate that ID830 is in a transitional phase where both the corona and the jet are energized following an accretion burst. The authors conclude that “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 the James Webb Space Telescope.”
This research not only enhances our understanding of quasars but also provides valuable insights into the behavior and characteristics of supermassive black holes and their environments. As astronomers continue to explore the universe, discoveries like that of ID830 deepen our comprehension of the cosmos and the phenomena that shape it.
