What the study found
The study found that higher companion-to-primary mass ratios can produce wider post-common-envelope separations in red giant binary interactions, but the widest separations they predicted were still smaller than the observed range. The authors also report that the inspiral becomes more stable around mass ratio q ≥ 1, and that fall-back material from the leftover bound envelope is a more likely source of circumbinary discs in their setup.
Why the authors say this matters
The authors are trying to explain post-red giant and post-asymptotic giant binary systems, which have longer periods and eccentric orbits than a standard common-envelope inspiral would leave. The study suggests that high mass ratio interactions and fall-back discs may help account for some of the observed features, although the abstract says their simulated separations remain too small.
What the researchers tested
The researchers carried out a series of three-dimensional hydrodynamical common-envelope binary interaction simulations using the smoothed particle hydrodynamics code Phantom. They modeled a 0.88 solar-mass, 90-solar-radius red giant branch star with companions spanning mass ratios q = M2/M1 from 0.68 to 1.5.
What worked and what didn't
Larger q values led to wider post-common-envelope separations, and the pre-common-envelope mass transfer phase lasted longer for more massive companions. Around q ≥ 1, the inspiral became significantly more stable, as predicted by analytical theory, but the abstract says this phase was not converged with respect to simulation resolution. Even with more material flowing through the L2 and L3 Lagrange points, the authors conclude that fall-back of bound envelope material is more likely than L2/L3 flow to form circumbinary discs for their parameters.
What to keep in mind
The abstract says the maximum predicted separation was only about 50 solar radii, which is still below the observed range for the systems they discuss. It also notes that the stability of the pre-inspiral phase was not converged with simulation resolution, so higher-resolution simulations are expected to give even more stability and a longer pre-inspiral phase. The available summary does not describe other limitations.
Key points
- Higher companion-to-primary mass ratios produced wider post-common-envelope separations.
- The widest predicted separation was still only about 50 solar radii, below the observed range.
- The inspiral became more stable around mass ratio q ≥ 1.
- The pre-common-envelope mass transfer phase lasted longer for more massive companions.
- The authors conclude that circumbinary discs are more likely to form from fall-back of bound envelope material than from L2/L3 outflow.
Disclosure
- Research title:
- High mass ratios widen post-common-envelope separations somewhat
- Authors:
- Jack Patrick Nibbs, Orsola De Marco, Lionel Siess, Ryosuke Hirai, Daniel J. Price
- Institutions:
- ARC Centre of Excellence for Gravitational Wave Discovery, Centre National de la Recherche Scientifique, Institut de Planétologie et d'Astrophysique de Grenoble, Macquarie University, Macquarie University, Monash University, Monash University, Université Grenoble Alpes, Université Libre de Bruxelles
- Publication date:
- 2026-01-01
- OpenAlex record:
- View
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