Prof. Bhal Chandra Joshi

While terrestrial detector, such as ALIGO, have heralded an era of Gravitational waves (GWs) by discovering high frequency GWs, a celestial instrument using an ensemble of radio pulsars is sensitive to ultra-low frequency GWs at the other end of GW spectrum. These GWs are produced by stochastic superposition of an ensemble of super massive black hole binaries (SMBHBs) or by inspiralling SMBHBs. In this talk, I will review the techniques used for detection of sub-microHz GWs with radio observations of millisecond pulsars and describe the major international experiments, including an emerging pulsar timing array experiment in India called Indian Pulsar Timing Array experiment (InPTA). This experiment provides critical input in terms of precision measurements of Dispersion measure of pulsars in the sample. Latest results on these and other contributions of InPTA consortium will be presented. While such GWs are yet to be detected, the limits obtained in pulsar timing arrays (PTA) already yield interesting results about galaxy merger rates and solar system dynamics. Latest PTA results indicate a weak correlated signal, which appears to make a detection imminent in next few years.