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The John D. and Catherine T. MacArthur Foundation has honored Kareem El-Badry, assistant professor of astronomy at Caltech, with a 2025 MacArthur Fellowship, which includes an unrestricted grant of $800,000. As stated by the foundation, these awards, commonly referred to as genius grants, recognize “exceptionally inventive individuals with a history of excellence in their field of study or area of practice.”
El-Badry has made various revelations related to stars and black holes by utilizing data from extensive astronomical surveys. In his initial work in 2018, he devised a novel technique for identifying binary stars—pairs of stars that can be challenging to tell apart due to their close proximity in the night sky. Leveraging information from the APOGEE (Apache Point Observatory Galactic Evolution Experiment) project, he detected over 3,000 binary systems in the Milky Way, and in subsequent investigations using data from the European Space Agency’s Gaia mission, he uncovered more than 1 million binaries—the largest known collection to date.
“I enjoy delving into new subfields and acquiring new knowledge, so I began to explore data from the Gaia mission after its initial major data release,” states El-Badry. “The data was incredible, and there were countless different types of sources that made it easy to be the first to examine some novel object and make a new discovery. I believe this is one of the most exciting aspects of astronomy compared to other sciences: There is a wealth of public data that allows anyone with an internet connection to make a discovery.”
When he learned about his MacArthur Fellowship, El-Badry expressed his astonishment. “Initially, I was convinced someone was attempting to deceive me,” he humorously remarks. “It feels wonderful to have my efforts acknowledged, and I consider myself fortunate to have been selected. My work is highly collaborative. In fact, the Gaia collaboration responsible for producing much of the data I utilize involves countless individuals, many of whom are not as visible, but without whom this work wouldn’t be achievable. I should also extend my gratitude to my students for their diligence in our research.”
El-Badry completed his undergraduate studies at Yale University and obtained his PhD in astrophysics from UC Berkeley. Prior to joining Caltech, he held a postdoctoral position at the Harvard & Smithsonian Center for Astrophysics. He maintains a visiting position at the Max Planck Institute for Astronomy in Heidelberg.
In additional research commencing in 2019, El-Badry unintentionally refuted seven claims of black hole discoveries, demonstrating that the suspected black holes were actually dim stars orbiting brighter stars.
In 2022, El-Badry and his colleagues identified the nearest known black hole to Earth, situated approximately 1,600 light-years away (for context, the center of our Milky Way galaxy is 25,000 light-years distant). The dormant black hole, named Gaia BH1, orbits a star similar to our Sun. Although it emits no light, El-Badry was able to detect the black hole due to the gravitational pull it exerts on its lighter stellar companion, akin to a parent swinging a toddler around.
“Kareem is an astronomer of exceptional creativity and profound physical insight. He is effecting significant shifts in our comprehension of the later stages of binary-star evolution through his innovative application of the vast Gaia dataset. He has discovered unseen companion stars and perplexing systems that challenge theoretical models formulated over decades to interpret earlier data,” states Hirosi Ooguri, the Fred Kavli Professor of Theoretical Physics and Mathematics and the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy at Caltech. “We are delighted that he has received this well-deserved accolade.”
Some of El-Badry’s recent discoveries include the 2024 revelation of 21 concealed neutron stars orbiting stars similar to our Sun. Like Gaia BH1, these obscured neutron stars were identified indirectly through the gravitational disturbances they created in their companion stars. Another recent investigation details the first-known “black hole trio,” a system comprising three stars, one of which is a black hole.
Looking forward, El-Badry is eager to analyze fresh data from Gaia as well as data from several NASA missions: SPHEREx, which launched this year; the forthcoming Nancy Roman Space Telescope, due to launch no later than May 2027; and NASA’s prospective UVEX mission. (Both SPHEREx and UVEX are overseen by Caltech).
“I am uncertain about exactly what I will be investigating,” remarks El-Badry, a member of the UVEX team, “but I am confident there will be new findings to uncover.”
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