When a couple's squabbling leads to cosmic bubbles

TL;DR

This paper reviews how binary star interactions influence planetary nebula shapes, emphasizing recent discoveries of binary central stars and evidence for mass transfer before the common envelope phase.

Contribution

It provides an overview of the binary hypothesis for planetary nebulae and discusses recent statistical and observational advances in the field.

Findings

Quadrupling of known post-common envelope binary central stars.

Evidence for mass transfer before the common envelope phase.

Insights into the role of binarity in nebula morphology.

Abstract

Binarity and mass transfer appear to play a key role in the shaping and, possibly, formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a quadrupling of the number of post-common envelope binary central stars of PNe compared to the end of the last century, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer - and accretion - prior to the common envelope phase.