Accurate Determination of Chemical Abundances near a Supermassive Black Hole

Abstract

The metal abundances in galactic nuclei carry key information on the history of star formation and mass transfer in central regions of galaxies. X-ray fluorescence analysis is a unique tool to reliably measure the abundances of various elements via simple physics. Here we present a new observation of the active nucleus in the Circinus Galaxy with the XRISM satellite at unprecedented X-ray energy resolution. The fluorescent iron-K$\alpha$ line profile modified by Compton scattering indicates that the material responsible for its emission is cold, metal-rich, and is located $\gtrsim$0.024 parsecs (pc) from the supermassive black hole, consistent with the dusty torus region. The abundance pattern derived from comparing fluorescent line intensities of different metals shows sub-solar ratios of argon- and calcium-to-iron, and a super-solar ratio of nickel-to-iron. This abundance pattern is best produced by a combination in number fraction of $92_{-4}^{+2}$\% core-collapse supernovae from progenitor stars less massive than $20_{-2}^{+3}{M}_{\odot }$ and $8_{-2}^{+4}$\% type-Ia SNe. This suggests that gas feeding the super-massive black hole was enriched by recent core-collapse supernovae. Our findings imply that in metal-rich environments stars more massive than about 20 $M_{\odot }$ directly collapse into black holes or make faint SNe without ejecting heavy metals into the space.

44 pages, 15 figures, 3 tables. Published in Nature Astronomy, 31 March 2026

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