…The universality of the UV-to-X-ray relation underpins certain methods that use quasars as “standard candles” to measure the geometry of the universe and ultimately probe the nature of dark matter and dark energy. This new result highlights the necessity for caution, demonstrating that the assumption of unchanging black hole structure across cosmic time must be rigorously re-examined…
i would rather bet that some gases or dust or whatever in the line of sight changes the ratio of X-ray and UV light.
Yeah, the chemistry of the medium changes over time to contain more metals. I wonder how much, or how fast the chemistry of the accretion disk changes too?