With no discovery of WIMPs to date, attention is turning towards lighter mass (sub eV) candidates for dark matter such as axion-like-particles. I will discuss their wave-like behaviour, and highlight the challenges in detecting signatures from such light particles in strong gravity environments. In particular, I will discuss accretion of such dark matter onto black holes, and its role in dynamical friction. Whilst challenging, such observations may be the only way to confirm the nature of dark matter, in the absence of any couplings to standard model particles.