Prof. Jasjeet Singh Bagla

Gravitational lensing was observationally verified more than a century ago. The last four decades have seen the gradual progression of gravitational lensing studies from a few isolated instances to a tool in astronomy. It is expected that the number of strong gravitational lenses will increase by more than an order of magnitude by the end of this decade. In the first part of the talk I will focus on studies of the so-called unstable singularities in gravitational lensing. I will introduce a method for constructing a map of all singularities of a gravitational lensing map. I will then use studies relying on this mapping of singularities to argue that the expected frequency of occurrence of such singularities has been vastly underestimated. We have shown that many instances of such singularities are expected to be discovered in observations by the JWST and other telescopes. We have enumerated the generic image formations for these singularities and also studied the stability of these image formations. We also show that the time delay characteristics of these singular points are very different from generic three and five image configurations. In the second half of the talk I will switch to gravitational lensing of gravitational waves. Given the low frequency and long wavelengths of gravitational waves that can be detected by present and upcoming detectors, the wave nature cannot be ignored, especially in micro-lensing. I will summarise some results related to micro-lensing of signals from sources with stochastic signals, e.g., core collapse supernovae.