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Axion lines from nuclear de-excitations in galactic stellar populations

Orion Ning1,2, Anupam Ray3, and Benjamin R. Safdi4,5,6

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Phys. Rev. D 113, 035010 – Published 11 February, 2026

DOI: https://doi.org/10.1103/xyjw-9bw7

Abstract

We show that mono-energetic axions are produced in abundance through nuclear de-excitations in nearby galaxies such as M87, which is the central galaxy of the Virgo cluster, and the starburst galaxy M82. If the axion couples to both nucleons and photons and is ultralight, then monochromatic hard x-ray signatures are induced by the subsequent axion-to-photon conversion in the magnetic fields permeating these systems. We search for evidence of such signals using NuSTAR data, focusing specifically on the Fe57 de-excitation line at 14.4 keV, and we catalog other potentially relevant nuclear lines. We find no evidence for axions from M87 or M82 and set stringent constraints on the combined axion-nucleon and axion-photon coupling at the level of |gann×gaγγ|≲1.1×10−22  GeV−1 in the limit ma≲10−10  eV at 95% confidence.

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Phys. Rev. D 113, 035010– Published 11 February, 2026
  • Received 10 November 2025
  • Accepted 21 January 2026
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