Search for Axion-like particles from nearby pre-supernova stars

¹ Julius-Maximilians-Universität Würzburg, Fakultät für Physik und Astronomie, Institut für Theoretische Physik und Astrophysik, Lehrstuhl für Astronomie Emil-Fischer-Str. 31 D-97074 Würzburg, Germany
² LAPTh, CNRS, USMB F-74940 Annecy, France
³ The Oskar Klein Centre, Department of Physics, Stockholm University Stockholm 106 91, Sweden
⁴ Centro de Astropartículas y Física de Altas Energías (CAPA), Universidad de Zaragoza Zaragoza 50009, Spain
⁵ Physical Sciences, Barry University 11300 NE 2nd Ave. Miami Shores Florida 33161, USA
⁶ Istituto Nazionale di Fisica Nucleare–Sezione di Bari Via Orabona 4 70126 Bari, Italy
⁷ Dipartimento Interuniversitario di Fisica Michelangelo Merlin Via Amendola 173 70126 Bari, Italy
⁸ The Hakubi Center for Advanced Research, Kyoto University, Yoshida Ushinomiyacho Sakyo-ku Kyoto 606-8501, Japan
⁹ Department of Physics, Kyoto University, Kitashirakawa Oiwake-cho Sakyo-ku Kyoto 606-8502, Japan
¹⁰ RIKEN Nishina Center, 2-1 Hirosawa Wako Saitama 351-0198, Japan
¹¹ Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo 5-1-5 Kashiwanoha Kashiwa Chiba 277-8583, Japan

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Received: 22 August 2025
Accepted: 17 December 2025

Abstract

Context. Axion-like particles (ALPs) are hypothetical pseudoscalar bosons that arise in many extensions of the Standard Model and can be well-motivated dark-matter candidates. Nearby massive stars in the late stages of stellar evolution provide a promising environment for enhanced ALP production due to their high core temperatures and densities.

Aims. In this work, we aim to search for a combined signal of ALP-induced hard X-ray and soft γ-ray emission from 18 nearby pre-supernova stars. We intend to use the full public INTEGRAL/SPI 22-year database to create individual datasets and link the resulting spectra for a coherent analysis.

Methods. We used a maximum-likelihood approach to extract the fluxes of the selected nearby stars from 20–2000 keV. From stellar-evolution models, we obtain the expected spectral shapes of ALPs producing processes peaking in the 50–500 keV range, depending on the age and mass of the star. We then constructed a joint likelihood that acknowledges the uncertainties in individual stellar parameters toward a combined estimate for the coupling constants g_aγ and g_ae as a function of the ALP mass m_a.

Results. We find that the hard X-ray and soft γ-ray fluxes of all selected stars are consistent with zero within uncertainties. We provide upper limits on the continuum flux as well as the 511 keV and 1809 keV lines from these sources. The combined estimate of the upper limit of the product g_aγ × g_ae is (0.008 − 2)×10⁻²⁴ GeV⁻¹ (95% C.I.) and the ALP-photon coupling g_aγ = (0.13 − 1.26)×10⁻¹¹ GeV⁻¹ (95% C.I.) up to a mass of m_a ≦ 10⁻¹¹ eV for different times to core-collapse and different magnetic-field models.

Conclusions. Our results are among the strongest limits on the ALP coupling constants in the literature. We also provide conservative limits on the coupling constants, g_aγ × g_ae, of (0.27 − 1.25)×10⁻²⁴ GeV⁻¹ (95% C.I.) by assuming all stars but one to be in the early He-burning phase. This work shows that soft γ-ray observations are required to efficiently probe the ALP parameter space, as well as massive-star evolution models in general.