Clumpy Heart of a Supernova express
When a star explodes, its material flies into space. In the supernova remnant SNR 0509-67.5, this material did not spread into a smooth cloud but gathered into separate clumps, like lumps in batter that is quickly stirred. The MUSE telescope in Chile saw these clumps in the faint glow of forbidden iron and calcium lines. Such lines only arise in very rarefied gas, so they clearly show where the ejected material is located.
The iron glow varies from clump to clump: some have more ionized atoms, others fewer. This allowed tracking how iron atoms lose electrons one by one as the shock wave catches up with them. It turned out that the clumps were denser than the surrounding gas even before the explosion — otherwise they could not glow so brightly in the iron-14 line. A computer model of a double white dwarf explosion showed that the Rayleigh-Taylor instability played the main role in forming the clumps: it arises when denser material pushes through less dense material, and the boundary between them becomes wavy.
Original abstract
as written by the authors arXiv:2608.17465v1
We report the discovery of a spatially resolved clumpy ejecta structure in the reverse-shocked ejecta of SNR 0509-67.5, revealed through multiple faint and broad forbidden coronal emission lines in deep MUSE observations. We also identify two new broad coronal emission lines not reported before in this remnant, [Fe xi] 7894 A and [Fe x] 6374.5 A , which extend the set of previously reported [Fe xv] 7059.59 A, [Fe xiv] 5302.86 A , [Fe ix] 8236.55 A , [Ca xv] 5695 A, and [S xii] 7611.0 A. Near-continuous ionisation states of Fe allow us to follow the ionisation progression behind the reverse shock. We use a 1D analytical model to evolve Fe charge states following reverse shock interaction to compare with observations, indicating the need for preshock clumping or over-density in order to reproduce the observed surface brightness of the [Fe xiv] line. Additionally, we report the spatially resolved distribution of ejecta clumps and show that reverse-shock interaction drives their compression and fragmentation. We also find a clear trend of decreasing velocity width with increasing Fe ionisation state, from the broadest [Fe ix] emission to the narrowest [Fe xv], with intermediate-ionisation species ([Fe x], [Fe xi], [Fe xiv]) showing intermediate widths. Finally, we compare our observations to a dynamically driven double-degenerate double detonation (D6) 3D remnant model at similar Fe and S ionisation states and conclude that the observed clumps are predominantly due to Rayleigh-Taylor instabilities.
The iron-14 line that revealed the clumps glows green — the same hue seen in auroras on Earth, though there it is produced by oxygen atoms.