Gravitational lensing, essentially bending of light rays in a gravitational field, has now been an established fact for more than a century. This field has seen rapid developments due to improvements in observations in the last half century. It can be shown that gravitational lensing leads to formation of multiple images if certain conditions are satisfied. Catastrophe theory can be used to further show that there are only five types of image formations possible with a single lens. Focus of most studies so far has been on two of these five types as these are known to be stable. I will summarise work that has been done on the remaining three types of image forms, of which two have now been observed in the sky. I will also outline potential applications of these image forms and expectations for coming years.
Jasjeet Singh Bagla is an astrophysicist by training. He studied at Delhi University and then did his PhD at IUCAA, Pune. His thesis work was primarily on gravitational clustering in an expanding universe. After postdoctoral stints at the Institute of Astronomy, Cambridge, UK, and the Harvard-Smithsonian Centre for Astrophysics, he joined the Harish-Chandra Research Institute in Allahabad. He continued working on cosmology and the high redshift universe. He took lead in setting up some of the earliest cluster computing platforms and used these for large scale simulations. After more than a decade at HRI Allahabad, he joined IISER Mohali to nurture his love of teaching. His research interests over the years have become more diverse, ranging from numerical relativistic studies of clustered dark energy to evolution of galaxies. He has mentored a number of students, some of whom have gone on to contribute significantly to research in astronomy and astrophysics. At present he is on sabbatical at NCRA-TIFR, Pune.
