Astrophysical Probes of Axion Like Particles: insights from Black holes, Galaxies and GW background

In this talk, I will present three studies exploring observable signatures of axion-like particles (ALPs) in different astrophysical environments. First, I will discuss photon–ALP conversion near the photon sphere of the supermassive black hole M87*, enabled by its surrounding magnetic fields.

This process can lead to a dimming of the photon ring, whose sensitivity to ALP mass and coupling opens up an observational window. Second, I will present constraints on eV-scale ALP dark matter derived from infrared to ultraviolet (IR–UV) observations of M87, using multi-instrument data from telescopes.

Finally, I will turn to supermassive black hole binaries, showing how their inspirals in the presence of ultralight dark matter through soliton formation in the galactic cores, can imprint signatures on the stochastic gravitational wave background. I will demonstrate how PTA may probe self-interaction properties of ultralight dark matter.