Hunting for traces of axions and axion-like particles with high-energy astrophysical observations

Axions and axion-like particles are hypothetical particles that are predicted in numerous extensions of the Standard Model. In addition to being a candidate for cold dark matter, the axion would also naturally explain the non-observation of the electric dipole moment of the neutron. These particles could be detected through their feeble interaction with photons in the presence of electromagnetic fields. In this talk, I will review how traces of this interaction could manifest themselves in astrophysical observations from X-ray to very high gamma-ray energies. In particular, spectra of bright active galactic nuclei have turned out to be a powerful tool in this endeavor, providing the most stringent bounds to date on the photon coupling for very light axion-like particles. Moreover, core-collapse supernovae have been identified as promising search targets. With several new observatories coming online in the 2020s, astrophysical observations will provide new opportunities for a discovery of these particles complementary to dedicated future laboratory searches.