Resumen: We present a novel approach to investigating axions and axionlike particles by studying their potential conversion into x-rays within the Sun’s atmospheric magnetic field. Utilizing high-sensitivity data from the nuclear spectroscopic telescope array (NuSTAR) collected during the 2020 solar minimum, along with advanced solar atmospheric magnetic field models, we establish a new limit on the axion-photon coupling strength ≲7.3×10−12 GeV−1 at 95% CL for axion masses ≲4×10−7 eV. This constraint surpasses current ground-based experimental limits, studying previously unexplored regions of the axion-photon coupling parameter space up to masses of ≲3.4 ×10−4 eV. These findings mark a significant advancement in our ability to probe axion properties and strengthen indirect searches for dark matter candidates. Idioma: Inglés DOI: 10.1103/18sn-hxtb Año: 2025 Publicado en: Physical Review Letters 135, 141001 (2025), 7 ISSN: 0031-9007 Tipo y forma: Article (Published version) Área (Departamento): Área Astronomía y Astrofísica (Dpto. Física Teórica) Área (Departamento): Área Física Atóm.Molec.y Nucl. (Dpto. Física Teórica)