Prof. B.C. Joshi

Over the last three decades, a community of radio astronomers and astrophysicists have been working on experiments, called pulsar timing arrays (PTAs),in an attempt to look for evidence of long wavelength Gravitational waves (GWs). The electromagnetic means for detection of these parsec wavelength waves has been precisely timing an ensemble of the best celestial clocks in our Galaxy, namely the radio millisecond pulsars, using the most sensitive radio telescopes in the world. Last month, in a coordinated publication of their results, five major experiments presented for the first time an emerging evidence of such GWs believed to be from a stochastic GW background formed by superposition of continuous GWs from an ensemble of super-massive black hole binary systems at the centres of merging galaxies. After a brief background of PTA experiments including the role of Indian Pulsar Timing Array collaboration (InPTA), these results will be presented with a discussion of employed analysis methods to separate noise sources covariant with the GW signal. While these results provide the first hint of an emerging GWB signal, these also raise new questions, which are likely to be examined in the upcoming combination of data of all PTA experiments under the auspices of international Pulsar Timing Array (IPTA). The presentation will conclude with a discussion of these questions and implications of our results outlining the road ahead in this emerging messenger.