A Wind-Driven Origin for the Firework Morphology of the Supernova Remnant Pa 30

TL;DR

Pa 30's firework-like morphology is explained by Rayleigh-Taylor instability (RTI) generated at the interface between a dense white-dwarf wind and the surrounding circumstellar medium, rather than by the original SN ejecta alone. With fiducial parameters such as a wind speed around a few ×10^3 km s^-1 and a wind-to-ambient density contrast of ~10^3, the RTI growth rate scales with wave number as ∝ k^{1/2} and the density contrast as (rho_a/rho_w)^{1/4}, yielding RTI development over ~1–10 years until rho_w ≈ rho_a and Rc ~ 10^{16–17} cm; Kelvin-Helmholtz instability remains suppressed during this phase due to the large density contrast and modest shear. Two-dimensional hydrodynamic simulations reproduce the observed filament speeds, densities (≈10^2–10^3 cm^-3), and temperatures (≈10^3–10^4 K), and naturally explain the filamentary central void as a consequence of the finite RTI duration rather than a wind termination shock. The framework implies that firework-like filaments can arise in other systems where a dense wind interacts with a relatively diffuse ambient medium, offering a new perspective on the morphologies of wind-dominated remnants and guiding future observations with facilities like JWST and HST.

Abstract

Pa 30 -- the likely remnant of the Galactic type Iax supernova of 1181 AD -- displays an unusual, firework-like morphology, consisting of radial filaments extending from a common center, where a white dwarf (WD) currently drives a very fast wind (speed $\gtrsim 10^{4}$ km s$^{-1}$). We propose the filaments arose from the Rayleigh-Taylor-unstable nature of the interface between the circumstellar medium (CSM) and the shocked wind launched by the natal WD; the filaments then elongated intact due to the Kelvin-Helmholtz-stable nature of the large initial density contrast between the wind and CSM, supplemented by the slowly declining wind density profile (relative to homologously expanding ejecta). To support this interpretation, we present two-dimensional hydrodynamical simulations and derive the filament properties, including their speed, density, and temperature, all of which are consistent with observations. We suggest the filaments elongate until the wind and CSM densities become comparable at the contact discontinuity, which occurs within 1--10 years, and then truncate because the RTI halts. The subsequent KHI growth timescale across the current width of the filaments is longer than the age of Pa 30, so they remain intact. The filament-less central region in Pa 30 is therefore more likely a consequence of the finite timescale over which the RTI operates, rather than a wind termination shock. In general, firework-like filaments may form in other systems, provided there is a sufficiently large density contrast between the ejecta and its surroundings.

Figures (2)

• Figure 1: Development of the RTI between an upper fluid with a density of 1 (in code units) and a lower fluid with a density of $0.5$ (left), 0.1 (middle), and 0.01 (right). The fluids are initially separated by a contact discontinuity at $y = 0.5$ and placed in a uniform gravitational field (magnitude $g = 1$; direction $-\hat{y}$), and an initial velocity perturbation of $-0.03 \sin \left(8\pi x\right)$ is imposed. The times in each panel correspond to when the downward-propagating plumes reach the bottom of the domain at $y \sim -1.5$.
• Figure 2: Photographs of the "Kingfish" high-altitude nuclear test (LA-UR-25-31831). The left image was taken ${\sim}40$ ms post-detonation, illustrating the formation of tendril-like filaments in the interior of the explosion. The right image was taken ${\sim}256$ ms post-detonation, showing the transformation of the firework-like filaments into a more cauliflower-like morphology reminiscent of standard supernova remnants. This terrestrial experiment suggests that homologous explosions may also pass through a Pa 30-like evolutionary phase that is (compared to wind-driven explosions) short-lived.