New research suggests that the environment surrounding supermassive black holes has evolved over billions of years, challenging long-held assumptions in astronomy. Observations indicate a significant change in the relationship between ultraviolet and X-ray emissions in quasars, as reported by an international group of astronomers led by the National Observatory of Athens. Their findings were published on December 27, 2025, in the Monthly Notices of the Royal Astronomical Society.
Quasars, first identified during the 1960s, are among the universe’s brightest objects. They derive their incredible luminosity from supermassive black holes that draw in surrounding matter. As this material spirals inward, it forms a rotating disk, heating up due to friction and emitting light that can surpass that of entire galaxies. This intense brightness allows quasars to be visible even from vast distances in the cosmos.
The study highlights the process by which ultraviolet light, emitted from the disk around a black hole, interacts with nearby energetic particles, transforming into high-energy X-rays. Historically, astronomers believed that there was a consistent relationship between the brightness of ultraviolet light and X-ray output, suggesting that the conditions surrounding black holes remained unchanged over cosmic time.
However, the new analysis reveals a different story. The team discovered that when the universe was approximately half its current age, the correlation between ultraviolet and X-ray emissions differed significantly from what is observed in nearby quasars today. This indicates that the dynamics of the accretion disk and the corona surrounding black holes have shifted over the last 6.5 billion years.
“This unexpected result challenges our understanding of how supermassive black holes grow and radiate,” said Dr. Antonis Georgakakis, one of the study’s authors. “We’ve confirmed this finding through various methods, and it has proven to be consistent.”
To arrive at these conclusions, the researchers utilized data from the eROSITA X-ray telescope combined with archival information from the European Space Agency’s XMM-Newton observatory. This combination allowed for an extensive examination of X-ray and ultraviolet emissions across a broad sample of quasars, a scale not previously achievable.
The implications of these findings are substantial for cosmology. The understanding that the ultraviolet and X-ray relationship in quasars is universal underpins various techniques that use quasars as standard candles for mapping the universe and studying dark matter and dark energy. The new evidence suggests that scientists should exercise caution, as the assumption of a static environment around black holes may not hold true.
“The key advance here is methodological,” explained Maria Chira, a postdoctoral researcher at the National Observatory of Athens and the study’s lead author. “The eROSITA survey is vast but relatively shallow, detecting many quasars with only a few X-ray photons. By employing a robust Bayesian statistical framework, we were able to uncover subtle trends that might otherwise have remained obscured.”
Looking ahead, upcoming scans from the eROSITA telescope will allow for the observation of even fainter and more distant quasars. By integrating these new observations with next-generation X-ray and multiwavelength surveys, researchers aim to further investigate whether the observed changes reflect genuine physical evolution or are artifacts of the data collection process. These ongoing efforts promise to yield deeper insights into how supermassive black holes drive the brightest objects in the universe and how their behaviors have transformed throughout cosmic history.
