The Serpent Eating Its Own Tail: Dust Destruction in the Apep Colliding Wind Nebula

November 2025 • 2025ApJ...994..121W

Authors • White, Ryan M. T. • Pope, Benjamin J. S. • Tuthill, Peter G. • Han, Yinuo • Dholakia, Shashank • Lau, Ryan M. • Callingham, Joseph R. • Richardson, Noel D.

Abstract • Much of the carbonaceous dust observed in the early Universe may originate from colliding wind binaries (CWBs) hosting hot, luminous Wolf─Rayet (W-R) stars. Downstream of the shock between the stellar winds there exists a suitable environment for dust grain formation, and the orbital motions of the stars wrap this dust into richly structured spiral geometries. The Apep system is the most extreme W-R CWB in our Milky Way: two W-R stars produce a complex spiral dust nebula, whose slow expansion has been linked to a gamma-ray burst progenitor. It has been unclear whether the O-type supergiant 0 .″ 7 distant from the W-R + W-R binary is physically associated with the system, and whether it affects the dusty nebula. Multiepoch Very Large Telescope/VISIR and JWST/MIRI observations show that this northern companion star routinely carves a cavity in the dust nebula—the first time such an effect has been observed in a CWB—which unambiguously associates the O star as a bound component to the Apep system. These observations are used together with a new geometric model to infer the cavity geometry and the orbit of the W-R + W-R binary, yielding the first strong constraints on wind and orbital parameters. We confirm an orbital period of over 190 yr for the inner binary—nearly an order of magnitude longer than the next longest-period dust-producing W-R CWB. This, together with the confirmed classification as a hierarchical triple, cements Apep as a singular astrophysical laboratory for studying colliding winds and the terminal life stages of the most massive star systems.

Links

• SIMBAD https://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2025ApJ...994..121W
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/adfbe1/pdf
• PREPRINT http://arxiv.org/abs/2507.14610
• DATA http://archive.eso.org/bin/ads2eso?2025ApJ...994..121W
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2025ApJ...994..121W
• DATA https://doi.org/10.17909/mf14-ga19
• DATA https://doi.org/10.5281/zenodo.15875502
• ELECTR https://doi.org/10.3847/1538-4357/adfbe1