Leading Axion-Photon Sensitivity with NuSTAR Observations of M82 and M87

We perform one of the most sensitive searches to date for the existence of ultralight axions using data from the NuSTAR telescope. We search for stellar axion production in the M82 starburst galaxy and the M87 central galaxy of the Virgo cluster and then the subsequent conversion into hard x-rays in the surrounding magnetic fields. We sum over the full stellar populations in these galaxies when computing the axion luminosity, and we account for the conversion of axions to photons by using magnetic field profiles in simulated IllustrisTNG analog galaxies. We show that analyzing NuSTAR data toward these targets between roughly 30 and 70 keV shows no evidence for axions and leads to robust constraints on the axion-photon coupling at the level of |g_{aγγ}|≲7.8×10^{-13} GeV^{-1} for m_{a}≲10^{-10} eV at 95% confidence.