Detecting individual stars at cosmological distances with gravitational lensing

Gravitational lensing refers to the bending of light rays coming from a distant source as they pass through the gravitational field of a mass distribution and has been a well established tool in astrophysics. One can show that, under certain conditions, gravitational lensing can lead to multiple image formations of the distant source and magnify these images. Recently, thanks to extreme lensing magnification boost, we have been able to detect and study individual stars halfway across the Universe. With the Hubble Space Telescope (HST) and JWST, the number of such objects has been continuously increasing. In my talk, I will discuss the basic idea behind how we search and detect these individual stars at cosmological distances and their applications. I will also talk about our recent detection of lensed star candidates in the MACS J0647.7+7015 galaxy cluster at a redshift of ≃4.8 when the Universe was only ~1.3 billion years old.