Identification of the Long-Sought Common-Envelope Events

TL;DR

This paper proposes a direct observational signature for common-envelope events (CEEs) based on a physical model of ejected matter cooling, matching observed red transient outbursts.

Contribution

It introduces a physical model linking CEE ejected matter cooling to observable signatures, providing direct evidence for CEEs.

Findings

Model predicts specific light-curve shapes and colors.

Ejection velocities and event rates align with observations.

Supports the occurrence of CEEs through observable signatures.

Abstract

Common-envelope events (CEEs), during which two stars temporarily orbit within a shared envelope, are believed to be vital for the formation of a wide range of close binaries. For decades, the only evidence that CEEs actually occur has been indirect, based on the existence of systems that could not be otherwise explained. Here we propose a direct observational signature of CEE arising from a physical model where emission from matter ejected in a CEE is controlled by a recombination front as the matter cools. The natural range of timescales and energies from this model, as well the expected colors, light-curve shapes, ejection velocities and event rate, match those of a recently-recognized class of red transient outbursts.