Abstract
The unresolved mysteries of the universe, including the nature of dark matter and the intricate dynamics of supermassive black holes (SMBHs), suggest that the Standard Model of particle physics remains incomplete, fueling the search for new physics beyond its boundaries. This thesis explores the detection of ultralight bosons—such as axions and dark photons—as prominent candidates for wave dark matter, with SMBHs serving as natural astrophysical laboratories for these investigations. We investigate two distinct detection strategies, each harnessing unique phenomena. First, we examine gravitational waves (GWs) detection, in the UGC4211 system, observations indicate the existence of a soliton, a self-gravitating configuration of wave dark matter, which we utilize to evaluate its influence on the stochastic gravitational wave background (SGWB) spectrum, particularly at low frequencies. Analysis of pulsar timing data from NANOGrav and EPTA, combined with constraints from dwarf galaxies, suggests axion mass and decay constant ranges of {ma, fa} ∼ {10−21.7 eV, 1015.5 GeV} and {ma, fa} ∼ {10−20.5 eV, 1016.8 GeV}, respectively. Second, we examine polarimetric detection, capitalizing on the superradiance process around SMBHs, such as M87∗ and Sgr A∗, where ultralight dark photons, produced via this mechanism, induce oscillating electromagnetic fields due to kinetic mixing with regular photons. Using Event Horizon Telescope measurements of Stokes parameters, we derive novel constraints on the photon-dark photon mixing parameter: for M87∗, limits are set over the dark photon mass range 10−22 eV to 10−20 eV, with a best reach of ∼ 10−8; for Sgr A∗, constraints apply to the range 10−19 eV to 10−17 eV, achieving a best reach of ∼ 10−10. These approaches underscore the potential of SMBH-hosted phenomena to elucidate the properties of ultralight bosons and their contribution to dark matter.