How does a supernova's blast wave tear through its own shell of ejected gas?

Astronomers tracked SN 2019vxm—a supernova that exploded into a dense shell of its own ejected material—across ultraviolet, optical, and infrared wavelengths for over four years. Early on, the blast wave heated and compressed this gas shell; around day 80–100, the shock broke through and the cooling cloud thinned out, exposing a recombination front. Dust in the outer layers then re-brightened around one year post-explosion, suggesting a second, denser shell farther out. The data points to an extraordinarily massive progenitor star shedding material at intense rates before it exploded.