Kailash Sahu, an astronomer at the Space Telescope Science Institute, will receive the 2026 Beatrice M. Tinsley Prize from the American Astronomical Society (AAS).

The prize, which is awarded every two years, recognizes an outstanding research contribution to astronomy or astrophysics of an exceptionally creative or innovative character. It is named in honor of astronomer Beatrice Tinsley (1941 – 1981), a pioneering expert on the evolution and aging of galaxies, as noted in a New York Times obituary. 

Sahu was recognized “for his groundbreaking work on relativistic deflection due to microlensing as a tool to detect isolated stellar-mass black holes and to measure the masses of stars and stellar remnants.”

Microlensing is a form of gravitational lensing in which the light from a background star is temporarily brightened and deflected by a massive object — such as a black hole — passing in front of it.

“I am thrilled to receive this award, which highlights the innovative nature and power of this method to weigh stars and stellar remnants, and to uncover hidden black holes. With the upcoming launch of the Nancy Grace Roman Space Telescope later this year, we will be able to apply this technique on an unprecedented scale, opening new windows into the study of these mysterious objects,” said Sahu.

Sahu’s research efforts have focused on applying microlensing, transit, and relativistic deflection techniques to detect and study exoplanets, nearby stars and black holes. He currently leads Hubble Space Telescope and James Webb Space Telescope projects aimed at detecting isolated, stellar-mass black holes and determining masses of stellar remnants through gravitational lensing.

In 2017, Sahu led the first ever measurement of relativistic deflection caused by a star outside the solar system, as predicted by Einstein just over a century ago, thereby measuring the mass of the nearby white dwarf Stein 2051 B — the first mass measurement through this technique. This work was listed by Discover magazine as one of the “Top 100 Science Stories” of 2017. Sahu used the same technique in 2023 to measure the mass of an isolated white dwarf, LAWD 37.

In 2022, Sahu and colleagues made the first — and to date, the only — unambiguous detection of an isolated stellar-mass black hole by measuring the relativistic deflection as it microlensed a background star. They determined that the black hole is located approximately 5,000 light-years from Earth, and weighs about 7 times as much as our Sun.

Sahu’s early work showed that the microlensing events detected towards the Magellanic Clouds are mainly caused by stars within those galaxies, and not by “massive compact halo objects” (MACHOs). He then cofounded the PLANET (Probing Lensing Anomalies NETwork) collaboration, to detect planets around lensing stars through frequent monitoring of microlensing events. This project has led to the discovery of several exoplanets, including terrestrial planets beyond the snow line, or distance from a young star where volatiles like water or carbon dioxide can condense.

Sahu led a program of Hubble observations which showed, for the first time, that a gamma-ray burst (GRB 970228) was associated with an external galaxy. He also led a large Hubble program called SWEEPS (Sagittarius Window Eclipsing Extrasolar Planet Search) which led to the discovery of 16 transiting planet candidates in the Milky Way’s galactic bulge, two of which were confirmed through radial velocity measurements. They remain among the most distant exoplanets detected to date.

Sahu has served as an instrument scientist for several instruments on the Hubble Space Telescope and the James Webb Space Telescope, including Hubble’s STIS (Space Telescope Imaging Spectrograph), ACS (Advanced Camera for Surveys), and WFC3 (Wide Field Camera 3), as well as Webb’s NIRCam (Near-Infrared Camera). He played a leading role in the design and implementation of the STIS exposure time calculators and led the instrument’s pipeline calibration group. After an irreparable failure in STIS’s primary electronics, he led the transition to its redundant system and oversaw all subsequent calibration activities. He also led ACS operational and calibration activities for Hubble Servicing Mission 4. In addition, Sahu led the WFC3 Point Spread Function (PSF) group, enabling the public release of approximately 24 million observed PSFs through the Hubble archive, and served as the Institute’s Operations Working Group Lead for NIRCam prior to Webb’s launch.

The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations center of the Hubble Space Telescope, the science and mission operations centers for the James Webb Space Telescope, and the science operations center for the Nancy Grace Roman Space Telescope. STScI also houses the Barbara A. Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives, and is the data repository for the Hubble, Webb, Roman, Kepler, K2, TESS missions and more. STScI is operated by the Association of Universities for Research in Astronomy in Washington, D.C.