Numerical models for the circumstellar medium around Betelgeuse

TL;DR

This paper uses hydrodynamic simulations of stellar evolution to model Betelgeuse's circumstellar medium, suggesting its bow shock may be a recent feature from a transition from blue to red supergiant.

Contribution

It introduces a novel 2D hydrodynamic model incorporating stellar evolution to explain Betelgeuse's circumstellar structures and bow shock features.

Findings

The bow shock around Betelgeuse may be a recent formation from a blue supergiant phase transition.

The model reproduces the observed bow shock and bar feature around Betelgeuse.

The outer shell could explain the bar feature observed ahead of Betelgeuse's bow shock.

Abstract

The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium out to at least 0.5 parsecs from its surface, shaped by its mass-loss history within the past 0.1 Myr, its environment, and its motion through the interstellar medium (ISM). In principle its mass-loss history can be constrained by comparing hydrodynamic models with observations. Observations and numerical simulations indicate that Betelgeuse has a very young bow shock, hence the star may have only recently become a RSG. To test this possibility we calculated a stellar evolution model for a single star with properties consistent with Betelgeuse. We incorporated the resulting evolving stellar wind into 2D hydrodynamic simulations to model a runaway blue supergiant (BSG) undergoing the transition to a RSG near the end of its life. The collapsing BSG wind bubble induces a bow shock-shaped inner shell which at least superficially resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We investigate whether this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.