Common envelope: progress and transients

Understand

We review the fundamentals and the recent developments in understanding of common envelope physics.

• We report specifically on the progress that was made by the consideration of the recombination energy.
• This energy is found to be responsible for the complete envelope ejection in the case of a prompt binary formation, for the delayed dynamical ejections in the case of a self-regulated spiral-in, and for the steady recombination outflows during the transition between the plunge-in and the self-regulated spiral-in.
• Due to different ways how the recombination affects the common envelope during fast and slow spiral-ins, the apparent efficiency of the orbital energy use can be different between the two types of spiral-ins by a factor of ten.