Long-term fate of the white dwarf with debris envelope

Determine the long-term evolution and ultimate fate of a white dwarf with debris envelope formed in a binary–supermassive-black-hole encounter by modelling thermal relaxation, nuclear burning, accretion onto the degenerate core, and mass loss from the envelope.

Background

The simulations end approximately 53 hours after pericentre, while the captured solar-like material remains an extended, non-degenerate envelope that has not reached hydrostatic or thermal equilibrium. In some cases, the total white-dwarf-plus-envelope mass exceeds the Chandrasekhar mass, although the degenerate core itself remains below that limit.

The ultimate outcome depends on the competition between accretion, nuclear burning, and mass loss. Possible outcomes include nova-like episodes, a thermonuclear explosion after sufficient core growth, or a peculiar red-giant-like configuration, but the simulations do not determine which outcome occurs.

References

This is set by the competition between accretion from the envelope and mass loss, and cannot be resolved by our simulations, which end long before the envelope has had time to evolve thermally. We do not expect an immediate Type~Ia supernova explosion, as the mass transfer occurs over a few hours, characterizing a highly dynamical, non-equilibrium accretion process. It is more probable that once the accretion rate onto the core exceeds the rate at which the accreted material can be burned stably, which for a WD of this mass is of order $10{-6}\,M_\odot\,\mathrm{yr{-1}$, a fraction of the material is expelled through nova-like episodes. Depending on the final mass retention, the WDDE might eventually undergo a thermonuclear explosion or settle into a peculiar red-giant--like configuration, as suggested by previous literature \citep[e.g.,][]{shara1977white,shara1986hydrodynamic, van20243d}.

— Tidal disruption of stellar binaries as a pathway to exotic transients  (2608.22735 - González-Servín et al., 24 Aug 2026) in Section 5.2, 'Fate of the WDDE'