Gravitational waves have offered us a whole new way of looking at our Universe. So far, we have seen them in the ~10-100 Hz range, and there are hints that we might soon see them in the nanohertz regime. However, there are parts of the frequency space that are currently not covered by any future or planned observations. I’ll give a brief overview of the gravitational wave spectrum and then explain how we can use the Roman Space Telescope’s Exoplanet Microlensing Survey to detect gravitational waves from the mergers of supermassive black holes in the microhertz regime.