Bipolar planetary nebulae from common-envelope evolution of binary stars

Abstract

Asymmetric shapes and evidence for binary central stars suggest a common-envelope origin for many bipolar planetary nebulae. The bipolar components of the nebulae are observed to expand faster than the rest, and the more slowly expanding material has been associated with the bulk of the envelope ejected during the common-envelope phase of a stellar binary system. Common-envelope evolution in general remains one of the biggest uncertainties in binary star evolution, and the origin of the fast outflow has not been explained satisfactorily. We perform three-dimensional magnetohydrodynamic simulations of common-envelope interaction with the moving-mesh code AREPO. Starting from the plunge-in of the companion into the envelope of an asymptotic-giant-branch star and covering hundreds of orbits of the binary star system, we are able to follow the evolution to complete envelope ejection. We find that magnetic fields are strongly amplified in two consecutive episodes: first, when the companion spirals in the envelope and, second, when it forms a contact binary with the core of the former giant star. In the second episode, a magnetically driven, high-velocity outflow of gas is launched self-consistently in our simulations. The outflow is bipolar, and the gas is additionally collimated by the ejected common envelope. The resulting structure reproduces typical morphologies and velocities observed in young planetary nebulae. We propose that the magnetic driving mechanism is a universal consequence of common-envelope interaction that is responsible for a substantial fraction of observed planetary nebulae. Such a mechanism likely also exists in the common-envelope phase of other binary stars that lead to the formation of Type Ia supernovae, X-ray binaries, and gravitational-wave merger events.

From 3D hydrodynamic simulations of common-envelope interaction to gravitational-wave mergers

“…The seed magnetic field is strongly amplified in our simulation (cf. Ohlmann et al 2016b), and magnetically driven bipolar outflows are observed similar to those in the CE simulation with a low-mass primary star of Ondratschek et al (2022). The magnetic-field energy saturates at around 10 45 erg, and the ratio of magnetic to kinetic energy never exceeds 3% in our simulations.…”

“…The NS and BH companions are not resolved and we do not consider accretion processes, jet launching, or neutrino cooling from such objects among other things. Similar simulations of CE interaction in lower mass systems with the arepo code were published by Ohlmann et al (2016a,b), Sand et al (2020), Kramer et al (2020), and Ondratschek et al (2022). We demonstrate that the high-mass star regime is accessible to current three-dimensional (3D) hydrodynamic simulations comprising the entire CE system and covering the full inspiral phase.…”

“…The magnetic-field energy saturates at around 10 45 erg, and the ratio of magnetic to kinetic energy never exceeds 3% in our simulations. The magnetic fields are irrelevant for the orbital evolution during the dynamic plunge-in of the CE phase and the ejection of the bulk of the hydrogen-rich envelope, similar to what is found in lower mass CE simulations by Ohlmann et al (2016b) and Ondratschek et al (2022). In the future evolution of the remaining binary systems, the magnetically driven outflow may affect the binary orbit.…”

“…5). We therefore expect the orbital separation to settle to a final value once the rest of the envelope material is expelled completely and the drag forces cease, as is the case in the CE simulations of lower mass stars of Ondratschek et al (2022). However, in our simulations with a massive primary star, the CFL-restricted time-steps become prohibitively small, preventing us from following the evolution over many more orbits.…”

The Common Envelope Origins of the Fast Jet in the Planetary Nebula M 3–38

“…Models predict that the orbit decays and orbital energy and angular momentum are transferred to the CE within a timescale of months to years (e.g., Chamandy et al 2020). The subsequent evolution naturally explains the formation of bipolar ejecta (see, e.g., Zou et al 2020;García-Segura et al 2021;López-Cámara et al 2022;Ondratschek et al 2022 and references therein) of material in the direction perpendicular to the orbital plane (see Hillwig et al 2016b). Indeed, high-resolution ALMA observations of water fountain objects, which are often interpreted as transitional sources between the AGB and proto-PNe phases, imply that they have experienced a recent (<200 yr) CE evolution (Khouri et al 2021).…”