TAPIR Seminar

Mergers of massive galaxies are thought to host binary supermassive black holes, which are driven to coalesce by their gravitational-wave emission. For the last decade, collaborations worldwide have been searching for signatures of these gravitational waves in millisecond radio pulsar timing data. The design sensitivities of these experiments, based on theoretical predictions, have now been surpassed. However, no gravitational waves have been detected. This startling result necessitates a shift in thinking on the fates of supermassive black holes in galaxy mergers, or indeed on the supermassive black hole occupation fraction. I will describe recent results from the Parkes Pulsar Timing Array collaboration, and their implications for supermassive black hole and galaxy assembly.