| Abstract: | Light (m < eV) bosonic particles (notably axions and relaxions) make interesting dark matter (DM) candidates, not least because they modify substructure in halos. Due to high occupation numbers typical of such candidates, gravitationally bound clumps of scalar field known as boson stars can form. I will briefly review what is presently known about the formation and stability of such configurations. For ultralight (or "fuzzy") DM, I will describe how simulations make concrete predictions that can be falsified by observations of the DM distribution in the cores of galaxies. Finally, I will outline recent work to constrain (rel)axion DM using atomic physics, and how a boson star 'halo' surrounding the Earth or Sun, consistent with existing constraints, can enhance local detection prospects. |