Astronomers have, for the first time, observed the exposed inner layers of a massive star as it exploded, according to a study published in Nature on 20 August. The event, designated supernova 2021yfj, lies roughly 2.2 billion light-years away and was initially detected by the Zwicky Transient Facility in September 2021 before being examined in detail with the W.M. Keck Observatory in Hawaii. The dying star had jettisoned not only its outer hydrogen and helium envelopes but also much of its dense silicon- and sulfur-rich shell, leaving the object “stripped to the bone,” said lead author Steve Schulze of Northwestern University. Spectra revealed unusually strong signatures of silicon, sulfur and argon—elements typically buried deep inside a star and therefore hidden during most supernova observations. Researchers say the finding confirms long-standing theoretical models of an onion-like internal structure in massive stars and points to a previously unclassified pathway to stellar death, in which violent mass-loss episodes precede the final blast. Whether those layers were ejected by extreme stellar winds, eruptive outbursts or interaction with a companion star remains unclear, and the team argues more examples will be needed to determine how common such stripped-core supernovae are.