Rapid Binary Mass Transfer: Circumbinary Outflows and Angular Momentum Losses
Creators
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1.
California Institute of Technology
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2.
University of California, Berkeley
Abstract
High rates of stable mass transfer likely occur for some binary star systems, but the resulting flow of mass and angular momentum (AM) is unclear. We perform hydrodynamical simulations of a polytropic donor star and a point-mass secondary to determine the mass, AM, and velocity of gas that leaves the system, and the dependence on binary parameters such as mass ratio. The simulations use an adiabatic equation of state and do not include radiative cooling or irradiation of the outflow. Mass transfer is initiated by injecting heat into the stellar envelope, causing it to gradually inflate and overflow its Roche lobe. The transferred mass flows into an accretion disk, but soon begins to escape through the outer Lagrange point (L2), with a lesser amount escaping through the L3 point. This creates an equatorially concentrated circumbinary outflow with an opening angle of 10°–30° with a wind-like density profile ρ ∝ r−2. We find that the ratios of the specific AM of the outflowing gas over that of the L2 point are approximately {0.95, 0.9, 0.8, 0.65} for mass ratios q = {0.25, 0.5, 1, 2} (accretor/donor). The asymptotic radial velocity of the outflowing gas, in units of the binary orbital velocity, is approximately 0.1–0.2 for the same mass ratios, except for q = 0.25, where it might be higher. This outflow, if ultimately unbound from the binary, may be a source of circumstellar material that interacts with ejecta from a subsequent supernova or stellar merger.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We are grateful for support from the NSF through grant AST-2205974. This research benefited from interactions enabled by the Gordon and Betty Moore Foundation through grant GBMF5076. Numerous conversations have helped lead this project to its current state. We thank Sterl Phinney for advice that initiated this project, Morgan MacLeod for help with the simulation setup, and Elias Most for advice on running the simulations on a cluster. We thank Dan Kasen and Tony Piro for useful feedback that generated more points of discussion. We are grateful to the organizers and participants of the 41ST Liége International Astrophysical Colloquium and the 2024 ZTF Theory Network Conference, at which we received advice and questions that led to new analysis. We thank the anonymous referee for providing thoughtful comments, which greatly improved this work. We also thank the data editor for providing feedback.
This work used the Purdue Anvil supercomputer through allocation PHY240274 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by U.S. National Science Foundation grant Nos. 2138259, 2138286, 2138307, 2137603, and 2138296.
Software References
PLUTO, Python, NumPy (C. R. Harris et al. 2020), Matplotlib (J. D. Hunter 2007), SciPy (P. Virtanen et al. 2020), Roche lobe calculator (D. A. Leahy & J. C. Leahy 2015), Roche_tidal_equilibrium5 (W. Lu 2025).
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Scherbak_2025_ApJ_990_172.pdf
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2505.21264 (arXiv)
Funding
- National Science Foundation
- AST-2205974
- Gordon and Betty Moore Foundation
- GBMF5076
Dates
- Accepted
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2025-07-14
- Available
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2025-09-05Published online