Quantify spin-orbit back-reaction effects in dynamically unstable triples

Determine whether including spin-orbit interactions and their back-reaction on the orbital dynamics of dynamically unstable triples significantly changes their black-hole-binary merger rates or merger properties.

Background

The simulations evolve black-hole spin precession but omit the corresponding spin-orbit back-reactions on the orbital motion. The omission is expected to be relatively unimportant for dynamically stable systems, whose inner orbital angular momentum is much larger than the spin magnitudes.

Dynamically unstable triples undergo chaotic close encounters and democratic interactions, where even small perturbations could alter the subsequent evolution. The paper therefore leaves unresolved whether spin-orbit back-reactions materially affect the predicted merger rates or observable merger properties of this population.

References

Whether or not this would have a noticeable effect on the merger rates or merger properties likely depends on the specific dynamics experienced by the unstable systems.

— Triple-induced mergers of black hole binaries: A comprehensive look at the role of stellar evolution, dynamical stability, and spin evolution  (2608.25538 - Bruenech et al., 26 Aug 2026) in Section 5.1, “Merger rates and model uncertainties”