In this talk, I will mainly discuss signatures of a QCD axion at aLIGO. In certain models of an axion, finite density corrections to the axion potential can result in the axion being sourced by large dense objects. There are a variety of ways to test this phenomenon, but perhaps the most surprising effect is that the axion can mediate forces between neutron stars (NS) that can be as strong as gravity. These forces can be attractive or repulsive and their presence can be detected by aLIGO observations of NS inspirals. By a numerical coincidence, axion forces between NS with gravitational strength naturally have an associated length scale of tens of kilometers or longer, similar to that of a NS. Future observations of NS mergers in aLIGO can probe many orders of magnitude of axion parameter space. I will also discuss some of the ongoing work related to signatures that result from violent stellar processes in the universe.
