This talk will explore how exciting astrophysical tools, such as gravitational-wave interferometers and the Event Horizon Telescope, can serve as powerful probes of new physics across vastly different mass scales. I will first show that data from the LIGO-Virgo-KAGRA Collaboration can help resolve a long-standing puzzle: whether the GeV gamma-ray excess at the Galactic Center originates from annihilating weakly interacting massive particles or from a population of millisecond pulsars. Turning to lighter dark matter candidates, I will then demonstrate how the same gravitational-wave detectors enable the direct detection of ultralight bosons, including dark photons, axions, and dilatons. Finally, I will extend this search to axions by shifting to the Event Horizon Telescope, showing how polarization measurements of black-hole images can reveal the presence of axion-like particles through their effects on photon birefringence. Together, these methods illustrate how these newly developed astrophysical frontiers can be repurposed as powerful discovery tools for new physics.
