Astronomers have captured unprecedented views of a massive star's final moments before it detonated as a supernova, an event that offers profound insights into stellar evolution. The supernova, designated SN 2021yfj, was observed and detailed in the journal Nature on August 20, 2025. This celestial event revealed a star that had shed its outer layers, exposing its inner core.
SN 2021yfj was first detected in September 2021 by the Zwicky Transient Facility (ZTF), a wide-field astronomical survey located east of San Diego, California. Situated approximately 2.2 billion light-years from Earth, the supernova occurred within a star-forming region. Its unusual chemical composition, rich in heavier elements like silicon, sulfur, and argon, strongly indicates that the progenitor star had shed its outer hydrogen and helium layers before its cataclysmic end. This observation provides direct evidence for the long-theorized layered structure of massive stars.
Steve Schulze, lead author and research associate at Northwestern University's CIERA, described the phenomenon as observing a star "essentially stripped to the bone." This rare glimpse into a star's internal composition just moments before its explosive demise corroborates theoretical models of stellar structure. Adam Miller, a senior author and assistant professor at Northwestern, remarked that the event "quite literally looks like nothing anyone has ever seen before," suggesting that these observations may challenge existing stellar evolution theories and point towards more exotic pathways for the demise of massive stars.
The collaborative effort involved observations from both the Zwicky Transient Facility and the W. M. Keck Observatory in Hawai'i. The Keck Observatory, known for its advanced spectrographic capabilities, was crucial in analyzing the light emitted by SN 2021yfj, allowing scientists to decipher its elemental composition. This research, supported by the National Science Foundation, not only provides valuable data on supernova processes and the internal structures of massive stars but also contributes significantly to our understanding of stellar life cycles and the chemical enrichment of galaxies.