Overview

• Northwestern-led researchers report in Nature that SN2021yfj exposed material from an inner shell, marking the first direct view of a massive star’s deep interior at explosion.
• Zwicky Transient Facility spotted the event in September 2021 about 2.2 billion light-years away, with a pivotal spectrum from W. M. Keck Observatory enabling detailed analysis.
• The supernova’s light was dominated by silicon, sulfur, and argon — elements rarely seen so prominently — signaling a progenitor stripped to oxygen–silicon layers, with material racing up to roughly 3,000 km/s.
• The team hypothesizes repeated, violent mass-loss episodes, potentially pair-instability pulses, whose expelled shells later collided with the explosion’s ejecta to power the observed brightness.
• Authors propose a possible new subtype, Type Ien, while stressing that the stripping mechanism remains uncertain and alternatives such as strong winds, a pre-supernova eruption, or companion interaction remain plausible.