Most of the "exploding stars" we use to measure the universe are actually blowing up inside the ghostly shells of dead stars.
arXiv · March 18, 2026 · 2603.16810
The Takeaway
These massive explosions are essential for measuring the expansion of the universe, but researchers found they may be occurring inside ancient planetary nebulae. This challenges the long-standing model of how these cosmic beacons form and could refine our understanding of cosmic distances.
From the abstract
I show that a newly estimated fraction of normal type Ia supernovae (SNe Ia) that interact within about 100 days of explosion with circumstellar material (CSM), called SNe Ia-CSM, is compatible with a recently estimated fraction of normal SNe Ia that interact with an old planetary nebula, hence, supporting the core-degenerate (CD) scenario for normal SNe Ia. According to the CD scenario, a white dwarf (WD) merges with the core of an asymptotic giant branch star at the end of common envelope evol