Erythrohenosis -- The crimson chronicles of two giants

TL;DR

This paper models the complex process of two red giants colliding and merging in dense stellar environments, predicting observable signatures across optical, nebular, and gravitational wave signals to aid future multi-messenger detections.

Contribution

It introduces an integrated end-to-end model combining simulations and analytical methods to characterize the entire evolution of red giant mergers, including gravitational wave signatures.

Findings

Grazing encounters lead to tidal capture and rapid orbital decay.

The merger produces a luminous precursor with quasi-periodic bursts.

The gravitational wave signal has a distinctive, rapidly evolving chirp.

Abstract

We investigate erythrohenosis -- the collision and merger of two red giants -- establishing an end-to-end model for this fundamental evolutionary channel in dense stellar environments. Combining three-dimensional SPH simulations of a binary with analytical modeling, we characterize the event from initial encounter to terminal explosion. We demonstrate that grazing encounters induce tidal capture and rapid orbital decay, accompanied by large-amplitude, nonlinear stellar oscillations. The subsequent inspiral spins up the common envelope into a stable, non-spherical equilibrium, powering a luminous precursor with quasi-periodic bursts. The terminal explosion, modeled with angular momentum conservation, produces an intrinsically flattened remnant that preserves a geometric memory, or morphomnesia, of its binary origin. The associated gravitational wave signal features a rapid, drag-dominated frequency evolution, identifiable by a unique time-varying apparent chirp mass. These results define a distinctive multi-stage observational fingerprint -- linking transient optical precursors, asymmetric nebulae, and anomalous gravitational wave chirps -- to guide identification in current and future multi-messenger surveys.