Supernovae drive large-scale, incompressible turbulence through small-scale instabilities

Abstract: The sources of turbulence in our Galaxy may be diverse, but core-collapse supernovae (SNe) alone provide enough energy to sustain a steady-state galactic turbulence cascade. By localizing and analyzing supernova remnants (SNRs) in high-resolution SNe-driven galactic disk cut-out simulations from Beattie et al. (2025), I show that SNRs radiate incompressible turbulence through baroclinic vorticity generation, localized at the interface where the hot and warm plasma phases mix near the cooling radius. I provide evidence that this process is seeded by a Vishniac (1994)-type instability, which corrugates and folds the interface. I present an analytical relation for a baroclinicity-fed incompressible mode spectrum, which matches that observed in the simulated SNRs. The unstable layer produces a spectrum of incompressible modes $\propto k^{-3/2}$ locally within the SNRs. Through the inverse cascade mechanism described and measured in Beattie et al. (2025), this opens the possibility that the $\propto k^{-3/2}$ spectrum, arising from corrugated folds in the unstable SNR layer, can imprint itself on kiloparsec scales, thereby connecting small-scale instabilities in the layer to the large-scale incompressible turbulence cascade.