The Very Large Detector - Pulsar TIming Arrays and the Detection of Low Frequency Gravitational Waves

Pulsar Astronomy has played a major role in the detection of gravitational waves. The first observational evidence of the existence of gravitational waves came via the observation by Joe Taylor and Joel Weisberg of gravitational radiation damping in the pulsar binary PSR 1913+16 discovered by Taylor and Russell Hulse. More recently a worldwide network of detector projects have been monitoring an ensemble of millisecond pulsars across the sky using radio telescopes around the world. Previously at the Jet Propulsion Laboratory it was realized by pioneers such as Frank Estabrook and Hugo Wahlquist,that deep space missions could be used as gravitational wave detectors by looking for alterations in the time of arrival of signals sent between Earth and the spaceship, which possessed an onboard clock. The same principle works if we use pulsars as clocks, so that gravitational waves travelling through space can be detected if they affect the time of arrival of signals from the pulsars here at the Earth. In June 2023 an international coalition of Pulsar Timing Arrays (PTAs) announced the detection of the low-frequency (NanoHertz band) gravitational wave background in the local Universe. The History that led up to this major event in the development of the field of gravitational wave detection will be presented in outline. One of the most interesting aspects of the history of PTAs is their interdisciplinarity. Amogst the pioneers of this field are pulsar astronomers like Donald Backer (who discovered the first millisecond pulsar, coined the term PTA and was a co-founder of the North American PTA NANOGrav), relativists like Steven Detweiler and NASA scientists like Ron Hellings and George Downs.