Astronomers have, for the first time, observed the innermost layers of a massive star as it detonated, capturing a detailed look at supernova 2021yfj in the Milky Way. The event, described in Nature by a team led by Northwestern University astrophysicist Steve Schulze, exposed dense shells of silicon and sulfur that are normally hidden by the outer envelopes of hydrogen and helium. Because those outer layers had already been lost before the explosion, the blast revealed what researchers call an “extremely stripped” supernova—a type long theorised but never directly confirmed. Data from the W.M. Keck Observatory and several other ground- and space-based telescopes show that the star had been shaved down almost to its core, offering a rare, layer-by-layer cross-section of stellar structure. The finding supports prevailing models of how heavy elements are forged inside massive stars and then dispersed into space by supernovae. It also raises new questions about how the progenitor shed so much material—whether through violent pre-supernova outbursts or interaction with a close companion star. Researchers plan follow-up observations to trace the supernova’s remnants and search for signs of a surviving companion. Further study could clarify the mechanisms that strip massive stars and refine estimates of how often such extreme explosions occur, deepening understanding of both stellar evolution and the chemical enrichment of galaxies.