Searching for coherent gravitational waves with relative stellar astrometry

While pulsar timing arrays (PTAs) have detected evidence for a nanohertz gravitational wave background from supermassive black hole binaries (SMBHBs), a coherent gravitational wave signal from individual binaries has not yet been detected. In this talk, we outline our efforts to detect coherent microhertz gravitational waves from SMBHBs, using relative stellar astrometry. Although the core principle of gravitational wave detection with astrometry is closely related to PTAs, analysis of astrometric data has unique challenges. Compared to PTAs and direct detection methods, the large (~ 10⁵) number of baselines and low (~ 10^-2) SNR per baseline make conventional Bayesian signal searches computationally expensive. We detail techniques we have developed to efficiently find individual SMBHB sources, as well as prospects for detection using the Kepler and Roman Space Telescope missions.