What the study found
The study found that higher companion mass ratios can produce wider orbits after a common-envelope event, which is an episode where two stars share a single outer envelope. Even so, the widest separation predicted here was still only about 50 solar radii, smaller than the observed range.
Why the authors say this matters
The authors say this matters because some post-red and post-asymptotic giant binaries have orbital properties that are hard to explain with standard common-envelope inspiral alone. The study suggests that higher mass ratios may help explain some of the observed behavior, and that the resulting circumbinary discs may be consistent with those seen in these systems.
What the researchers tested
The researchers ran three-dimensional hydrodynamical common-envelope simulations using the smoothed particle hydrodynamics code Phantom. They modeled a red giant branch star of 0.88 solar masses and 90 solar radii, with companions chosen to give mass ratios from 0.68 to 1.5.
What worked and what didn't
Larger mass ratios generally led to wider post-common-envelope separations. Around mass ratio q greater than or about 1, the inspiral became more stable and the pre-common-envelope mass-transfer phase lasted longer, although this part of the calculation was not converged with simulation resolution. The study also found that circumbinary discs are more likely to form from fallback of leftover bound envelope material than from material flowing through the L2 and L3 Lagrange points.
What to keep in mind
The authors note that the mass-transfer and inspiral phase around q greater than or about 1 was not converged with respect to resolution, so higher-resolution work may change the degree of stability and the length of that phase. The simulations covered one giant-star model and a limited range of mass ratios, so the results apply only within those parameters. The abstract does not describe additional limitations.
Key points
- Higher companion mass ratios produced wider post-common-envelope separations.
- The widest predicted separation was about 50 solar radii, still below the observed range.
- For q greater than or about 1, the inspiral became more stable and pre-inspiral mass transfer lasted longer.
- The pre-inspiral phase was not converged with simulation resolution.
- Circumbinary discs were judged more likely to come from fallback of leftover bound envelope material.
Disclosure
- Research title:
- High-mass companions can widen common-envelope outcomes in giant stars
- 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, Macquarie University, Macquarie University, Monash University, Monash University, Pioneer (United States), Université Grenoble Alpes, Université Libre de Bruxelles
- Publication date:
- 2026-01-01
- OpenAlex record:
- View
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