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

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

arXiv · 2507.14610

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

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

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Abstract

Much of the carbonaceous dust observed in the early universe may originate from colliding wind binaries (CWBs) hosting hot, luminous Wolf-Rayet (WR) stars. Downstream of the shock between the stellar winds there exists a suitable environment for dust grain formation, and the orbital motion of the stars wraps this dust into richly structured spiral geometries. The Apep system is the most extreme WR-CWB in our Milky Way: two WR 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 WR+WR binary is physically associated with the system, and whether it affects the dusty nebula. Multi-epoch VLT/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 WR+WR binary, yielding the first strong constraints on wind and orbital parameters. We confirm an orbital period of over 190 years for the inner binary - nearly an order of magnitude longer than the next longest period dust-producing WR-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.

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Ryan M. T. White, Benjamin J. S. Pope, Peter G. Tuthill, Yinuo Han, Shashank Dholakia, Ryan M. Lau, Joseph R. Callingham, Noel D. Richardson. 2025-07-19. The Serpent Eating Its Own Tail: Dust Destruction in the Apep Colliding-Wind Nebula. https://arxiv.org/abs/2507.14610

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