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arXiv · 2502.00111

Stellar mergers and common-envelope evolution

Fabian R. N. Schneider·Mike Y. M. Lau·Friedrich K. Roepke
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Abstract

Stellar mergers and common-envelope evolution are fast (dynamical-timescale) interactions in binary stars that drastically alter their evolution. They are key to understanding a plethora of astrophysical phenomena. Stellar mergers are thought to produce blue straggler stars, blue supergiants, and stars with peculiar rotation and surface chemical abundances. Common-envelope evolution is proposed as a key stage in the formation of gravitational wave sources, X-ray binaries, type Ia supernovae, cataclysmic variables, and other systems. A significant fraction (tens of percent) of binary stars undergo such a phase during their evolution. In this chapter, we first discuss processes leading to a stellar merger or common-envelope phase. We then explain these complex interactions, starting from underlying physical principles like entropy sorting in stellar mergers and the energy formalism in common envelopes. This is followed by a more complete picture revealed by three-dimensional (magneto)hydrodynamical simulations. The outcomes of these interactions are discussed comprehensively and special emphasis is given to the role of magnetic fields. Both stellar mergers and common-envelope evolution remain far from fully understood, and we conclude by highlighting open questions in their study.

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Fabian R. N. Schneider, Mike Y. M. Lau, Friedrich K. Roepke. 2025-01-31. Stellar mergers and common-envelope evolution. https://arxiv.org/abs/2502.00111

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