Searching for Axionlike Particles with X-Ray Observations of Alpha Centauri

We investigate the production of axionlike particles (ALPs) in stellar cores, where they interact with electromagnetic fields and electrons, with typical masses between O(0.1) and O(10)  keV. These low-energy ALPs are gravitationally trapped in the orbits of stars and subsequently decay into two photons that we detect as monochromatic x-ray lines. We propose to search for these gravitationally trapped ALPs in the Alpha Centauri binary system, our closest stellar neighbor, using sensitive x-ray detectors like Chandra and eROSITA. Our search for ALP decay signals in the energy range of 0.2 keV to 10 keV yielded null results, thus establishing the most stringent limits on ALP interactions to date. In the case of ALP-electron coupling g_{aee}≤10^{-15}, we have improved the limits on the ALP-photon coupling g_{aγγ} in ALP mass range between 0.25 keV and 5 keV, compared to previous measurements, including those from GW170817, SN 2023ixf, and other sources, and specially the improvement reaches about 2 orders of magnitude at the mass of 2 keV. Even tighter constraints are set for larger g_{aee}.