When Stars Fail to Explode — Pa 30's Unusual Filaments

Pa 30 formed when a white dwarf's explosion fizzled: a surviving star launched dense ~15,000 km/s winds and Rayleigh–Taylor instabilities produced its straight filaments.

Pa 30 (SNR 1181) is an unusual supernova remnant whose long, straight filaments trace back to a “guest star” recorded in 1181. Eric Coughlin (Syracuse University) proposes that the progenitor was a white dwarf that experienced a failed Type Iax explosion: surface nuclear burning did not transition to a full detonation, leaving a hyper‑massive white dwarf at the centre that continued to drive a fast, dense wind enriched with heavy elements. How a failed explosion made filaments Coughlin's picture is that the surviving white dwarf launched an extraordinarily fast wind (roughly 15,000 km/s) that pushed into much lighter surrounding gas. At the boundary the Rayleigh–Taylor instability formed finger‑like plumes; because the wind remained dense and was continually fed by the remnant, those plumes elongated into the straight filaments now observed. Why the filaments stayed straight Normally a secondary instability mixes and shreds such fingers into chaotic, cauliflower‑like shapes characteristic of most supernova remnants. In Pa 30 the density contrast between the wind and the ambient material was high enough that the second, shredding instability did not grow, so the filaments persisted and stretched outward rather than breaking apart. Simulations and parallels Coughlin includes simulations showing that very high density contrasts reproduce filamentary structures like those in Pa 30. The work also notes an unexpected visual analogy with declassified images from the 1962 Kingfish nuclear test, where early filamentary patterns briefly appear before later evolving into more chaotic forms—the difference being that Pa 30’s wind kept its filaments growing. Broader implications This scenario places Pa 30 in the Type Iax class of partial thermonuclear explosions, a rare but increasingly recognised subclass. The remnant provides a modern modelling link to the historical 1181 observation and suggests that similar filamentary patterns might appear in other astrophysical events involving dense outflows, such as some tidal disruption events. Suggestions Further multiwavelength observations of Pa 30 and searches for similar filamentary remnants could test how common such failed explosions are. Continued numerical modelling of dense, sustained winds and comparisons with historical records and analogue datasets may clarify when and where Type Iax remnants leave this distinct signature.