7453 20250128080723.0 10.1126/science.adg7700 DOI SCART-2025-0084 Frost, A. J. A magnetic massive star has experienced a stellar merger 2024 Massive stars (those ≥8 solar masses at formation) have radiative envelopes that cannot sustain a dynamo, the mechanism that produces magnetic fields in lower-mass stars. Despite this, approximately 7% of massive stars have observed magnetic fields, the origin of which is debated. We used multi-epoch interferometric and spectroscopic observations to characterize HD 148937, a binary system of two massive stars. We found that only one star is magnetic and that it appears younger than its companion. The system properties and a surrounding bipolar nebula can be reproduced with a model in which two stars merged (in a previous triple system) to produce the magnetic massive star. Our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers. NO Sana, H. Mahy, L. Wade, G. Barron, J. Le Bouquin, J. -B. Mérand, A. Schneider, F. R. N. Shenar, T. Barbá, R. H. Bowman, D. M. Fabry, M. Farhang, A. Marchant, P. Morrell, N. I. Smoker, J. V. Science 384 2024 6692 214-217 laurent.mahy@ksb-orb.be 8117195 http://publi2-as.oma.be/record/7453/files/Frost_Science_HD148937.pdf 3101 http://publi2-as.oma.be/record/7453/files/Frost_Science_HD148937.gif?subformat=icon icon 3975 http://publi2-as.oma.be/record/7453/files/Frost_Science_HD148937.jpg?subformat=icon-180 icon-180 published in REFERD