I am an Astronomer, and an Instrument Scientist for the WFC3 instrument on board the Hubble Space Telescope. My research efforts have focused on applying microlensing, transit, and relativistic deflection techniques to detect and study exoplanets, nearby stars and black holes. I currently lead two HST projects to detect isolated, stellar-mass black holes and determine their masses through gravitational lensing.

We recently reported the first unambiguous detection and mass measurement of an isolated stellar-mass black hole. Here is a copy of the paper published in ApJ.

Back in 1994, I had shown that the microlensing events detected towards the Magellanic Clouds are mainly caused by the stars within the Magellanic Clouds, and not by MACHOs (Sahu, 1994, Nature, 370, 275). This naturally led to the idea that, if the lensing stars have planets around them, they should cause extra features in the microlensing lightcurve. So I co-founded the PLANET (Probing Lensing Anomalies NETwork) collaboration to detect planets around the lensing stars through frequent monitoring of microlensing events. This project has led to the discovery of several exoplanets, including terrestrial planets.

I led a program of HST observations which showed, for the first time, that a Gamma Ray Burst (GRB 970228) was associated with an external galaxy, and that the GRB phenomenon is unrelated to the nuclear activity of the host galaxy (Sahu et al. 1997, Nature, 387, 479).

I led a large HST program called SWEEPS (Sagittarius Window Eclipsing Extrasolar Planet Search) which monitored ~300,000 stars towards Galactic bulge using the Hubble Space Telescope to look for planets through transits. This led to the discovery of 16 planet candidates in the Galactic bulge; these planet candidates remain the farthest planets detected to date (Sahu et al. 2006, Nature, 443, 1038).

Recently, I led the first ever measurement of relativistic deflection caused by a star outside the solar system (the nearby white dwarf Stein 2051 B), as predicted by Einstein just over a century ago. The relativistic deflection was used to measure the mass of the white dwarf, the first such measurement through this technique (Sahu et al. 2017, Science, 356, 1046). This work was listed by Discover magazine as one of the "Top 100 Science Stories" of 2017.