2025NatAs...9..720T

Quasars, powered by supermassive black holes, are among the brightest objects in the Universe. In the vicinity of a supermassive black hole, X-ray photons from an active galactic nucleus can heat the surrounding gas to several hundred kelvin. Here we report observations of dust continuum and carbon monoxide (CO) J = 13-12 and J = 14-13 line emissions at a resolution of 130 pc in a luminous quasar at a redshift of 6. We successfully detected these high- J CO line emissions from warm gas in a compact disk component. The CO luminosity ratio in the central region of the compact disk is consistent with theoretical models in which X-ray heating dominates the CO excitation and the gas column density is as high as 10²⁵ cm^–2. This finding demonstrates that high-resolution observations of high- J CO lines are promising ways to identify extremely dust-obscured quasars in the early Universe.