Nanohertz Gravitational Waves from Pulsar Timing Arrays

Pulsar timing arrays (PTAs) use observations of millisecond pulsars to detect nanohertz gravitational waves. In June 2023, 4 PTAs presented the results of such searches in their datasets and found compelling evidence for the spatial correlations characteristic of the gravitational wave background. I will introduce how we search pulsar timing array data for gravitational wave signals and summarize the results of recent searches of the European PTA data.