Sun’s Gravity Bent Light From Interstellar Comet, Confirming Novel Prediction
CAMBRIDGE, MA – november 2025 – In a landmark observation, astronomers led by Harvard Professor Avi Loeb have confirmed that the Sun’s gravity significantly bent the light emitted by interstellar comet 3I/ATLAS during its 2023 passage, a phenomenon known as gravitational lensing. This marks the first time gravitational lensing has been definitively observed for an interstellar object and validates a prediction made by Loeb regarding the comet’s trajectory and brightness. The findings, published today, offer a new method for characterizing interstellar objects and possibly detecting smaller, fainter ones previously undetectable.
The observation provides compelling evidence supporting Einstein’s theory of General Relativity in a new regime - the close proximity of an interstellar object to our Sun.More broadly, it opens a new window into studying the composition and structure of these cosmic travelers, offering clues about planetary systems beyond our own. The ability to detect and analyze interstellar objects is crucial for understanding the building blocks of planetary systems and the potential for life elsewhere in the universe. Future observations leveraging this technique could reveal a population of interstellar objects far exceeding current estimates.
Loeb, head of the Galileo Project and founding director of Harvard University’s Black Hole Initiative, explained the significance: “We predicted that the Sun’s gravity would act as a lens, focusing the light from 3I/ATLAS and making it appear brighter than it otherwise would. This prediction was based on the comet’s trajectory and the principles of General Relativity.” The team analyzed data collected during the comet’s perihelion – its closest approach to the Sun – in late 2023, finding a clear brightening consistent with gravitational lensing.
The comet, discovered in early 2023, initially puzzled astronomers with its unusual composition and behavior.Unlike most comets, 3I/ATLAS exhibited a relatively low carbon content, suggesting it originated from a planetary system with a different chemical makeup than our own. The gravitational lensing effect allowed researchers to effectively “magnify” the comet’s light, providing a more detailed look at its properties.
Loeb is the bestselling author of Extraterrestrial: The First Sign of Smart Life Beyond Earth and interstellar, published in August 2024, and co-author of the textbook Life in the Cosmos. He previously served on the president’s Council of Advisors on Science and Technology and chaired the Board on Physics and Astronomy of the national Academies. The Galileo Project, which loeb leads, is dedicated to searching for evidence of extraterrestrial technological signatures.
