Dark matter may leave observable signatures in gravitational-wave detectors through a remarkably broad range of physical mechanisms. In this talk, I will discuss recent searches using data from the fourth observing run of the LIGO–Virgo–KAGRA detector network. First, I will present a direct search for ultralight dark matter, in which coherently oscillating scalar, vector, and tensor fields can produce characteristic signals in gravitational-wave interferometers. I will then discuss searches for gravitational waves from inspiraling planetary-mass and asteroid-mass ultra-compact objects, which could be primordial black holes. Finally, I will discuss how related searches for persistent, quasi-monochromatic gravitational waves can probe ultralight bosons through gravitational radiation from boson clouds surrounding rotating black holes. Together, these searches illustrate how gravitational-wave detectors can function not only as observatories of conventional astrophysical sources, but also as sensitive experiments for exploring the nature of dark matter.
