The John D. and Catherine T. MacArthur Foundation has awarded Kareem El-Badry, assistant professor of astronomy at Caltech, with a 2025 MacArthur Fellowship, an honor that comes with a "no-strings-attached" grant of $800,000. According to the foundation, the awards, known colloquially as genius grants, honor "extraordinarily creative individuals with a track record of excellence in a field of scholarship or area of practice."
El-Badry has made numerous discoveries involving stars and black holes using datasets from large astronomical surveys. In early work in 2018, he developed a new method for identifying binary stars—pairs of stars that can be hard to distinguish due to their close proximity to each other in the sky. Using data from the APOGEE (Apache Point Observatory Galactic Evolution Experiment) project, he found over 3,000 binary systems in the Milky Way, and in later work using data from the European Space Agency's Gaia mission, he discovered more than 1 million binaries—the largest known sample to date.
"I like to explore new subfields and learn new things, and so I started playing with data from the Gaia mission after its first big data release," El-Badry says. "The data were amazing, and there were so many different kinds of sources that it was easy to be the first person to look at some new object and discover something new. I think this is one of the best things about astronomy relative to other sciences: There is so much public data that anyone with an internet connection can make a discovery."
Upon hearing the news of his MacArthur Fellowship, El-Badry says he was very surprised. "At first, I was pretty sure someone was trying to scam me," he jokes. "It feels great to have my work recognized, and I feel lucky to have been chosen. My work relies heavily on collaboration. In fact, the Gaia collaboration that produces a lot of the data I work with involves hundreds of people, many of whom are less visible but without whom the work wouldn't be possible. I can also thank my students for the hard work they put into our research."
El-Badry attended Yale University as an undergraduate and earned his PhD in astrophysics from UC Berkeley. Before coming to Caltech, he held a postdoctoral position at the Harvard & Smithsonian Center for Astrophysics. He continues to hold a visitor appointment at the Max Planck Institute for Astronomy in Heidelberg.
In research beginning in 2019, El-Badry inadvertently debunked seven claims of black hole discoveries, showing that suspected black holes were, in fact, faint stars orbiting other brighter stars.
In 2022, El-Badry and his colleagues discovered the closest known black hole to Earth, lying about 1,600 light-years away (for reference, the center of our Milky Way galaxy is 25,000 light-years away). The inactive, or dormant, black hole, dubbed Gaia BH1, orbits a star like our Sun. Though it emits no light, El-Badry was able to spot the black hole through a gravitational tug it induces on its lighter-weight stellar companion, like a parent swinging around a toddler.
"Kareem is an astronomer with extraordinary creativity and deep physical intuition. He is driving major changes in our understanding of the late stages of binary-star evolution through his innovative use of the enormous Gaia dataset. He has discovered invisible companion stars and puzzling systems that challenge theoretical models developed over decades to explain earlier data," says 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 thrilled that he has received this well-deserved honor."
Some of El-Badry's recent findings include the 2024 unveiling of 21 hidden neutron stars orbiting around stars like our sun. Like Gaia BH1, these dark, or hidden, neutron stars were spotted indirectly through gravitational wobbles induced in their partner stars. Another recent study describes the first-known "black hole triple," a system of three stars, one of which is a black hole.
Looking ahead, El-Badry is excited to analyze new data from Gaia as well as data from several NASA missions: SPHEREx, which launched this year; the upcoming Nancy Roman Space Telescope, set to launch no later than May 2027; and NASA's future UVEX mission. (Both SPHEREx and UVEX are led by Caltech).
"I don't know exactly what I'll be looking for," says El-Badry, who is a member of the UVEX team, "but I'm sure there will be new things to be found."