Remnant from a D6 thermonuclear supernova, 500 yr after the explosion, from Ferrand et al 2022. D6 stands for dynamically-driven (violent mass transfer) double-degenerate (two white dwarfs orbiting each other) double-detonation (first in the outer He layer, then in the C+O core, of the primary WD).
Shown is the shell of shocked matter, in one hemisphere. Layers of shocked ejecta are in cool colours, from green at the reverse shock to blue at the contact discontinuity. Layers of shocked interstellar medium (ISM) are in warm colours, from purple at the forward shock to red at the contact discontinuity. The shocks are rendered as semi-transparent surfaces.
The interface between the ejecta and the ISM is deformed by the Rayleigh-Taylor instability that develops during the remnant phase. The region with a flatter reverse shock and reduced instability is a shadowing effect from the surviving white dwarf, the companion of the exploded white dwarf.