Testing the ALP-photon coupling with polarization measurements of Sagittarius A

Ultra-light bosons such as axions or axion-like particles (ALPs), are promising candidates to solve the dark matter problem. A unique way to detect such ALPs is to search for the periodic oscillation feature of the position angles of linearly polarized photons emitted from the galaxy center. In this work, we use the high-resolution polarimetric measurements of the radiation near the super-massive black hole (SMBH) in the center of the Milky Way, i.e., Sagittarius A(star) (Sgr A(star)), by a sub-array of the Event Horizon Telescope to search for the ultra-light ALPs. We derive upper limits on the ALP-photon coupling of similar to 10(-12) GeV-1 for ALP masses of m(a) similar to (10(-19) - 10(-18)) eV, with a solitonic core + NFW dark matter density profile. Our results are stronger than that derived from the observations of SN1987A and a population of supernovae in the mass window of (10(-19) - 10(-17)) eV. Improved polarimetric measurements with the full Event Horizon Telescope can further strengthen the constraints.

Automated summary

The study utilizes high-resolution polarimetric measurements near the super-massive black hole in the center of the Milky Way to search for ultra-light ALPs, resulting in upper limits on the ALP-photon coupling. The findings are stronger than those derived from previous observations.