Post–accretion-induced collapse (AIC) outcome of FQ Cir

Determine the dynamical and evolutionary outcome of FQ Circini immediately following the accretion-induced collapse of its oxygen–neon white dwarf to a neutron star, specifically the fate of the common envelope and the surviving core of the B1 V(n)(e) companion, and whether the system emerges as a neutron-star–helium-star binary or proceeds to further collapse to a black hole.

Background

The paper argues that sustained mass transfer could grow the mass of the oxygen–neon (ONe) white dwarf in FQ Cir to near the Chandrasekhar limit, at which point an accretion-induced collapse (AIC) to a neutron star is expected rather than a Type Ia supernova. However, the authors explicitly state uncertainty about what happens immediately after the AIC, including the behavior of the envelope and the companion’s core.

Resolving the post-AIC outcome is central to predicting the long-term fate and observational signatures of FQ Cir (e.g., whether it becomes a neutron-star–helium-star binary or evolves further to a black hole), and would clarify evolutionary pathways for high-mass cataclysmic variables (HMCVs).

References

After the collapse to a NS, we do not know what will happed to the envelope and the surviving core of the companion. Perhaps a clear binary will appear consisting of a NS and a helium star, all in a tight orbit. Perhaps enough mass will land onto the NS so that it will collapse quietly to a BH, perhaps still in a tight orbit with the core of the companion.

— FQ Circini: An Ordinary Nova with a High-mass B1 V(n)(e) Companion Whose Decretion Disk Transfers Mass to the White Dwarf via Roche-Lobe Overflow  (2511.16594 - Schaefer et al., 20 Nov 2025) in Section 5.3 (The future evolution)