3D Simulations of Betelgeuse's Bow Shock

TL;DR

This paper presents the first 3D hydrodynamic simulations of Betelgeuse's bow shock, revealing how different instabilities shape its structure and indicating the star's recent transition into the red supergiant phase.

Contribution

The study introduces realistic 3D simulations of Betelgeuse's bow shock, exploring the effects of instabilities and star's recent evolution, which were not previously modeled in detail.

Findings

Bow shock morphology varies with stellar velocity due to different instabilities.

The bow shock is likely very young and not in steady state.

Betelgeuse's recent entry into the red supergiant phase is suggested.

Abstract

Betelgeuse, the bright, cool red supergiant in Orion, is moving supersonically relative to the local interstellar medium. The star emits a powerful stellar wind which collides with this medium, forming a cometary structure, a bow shock, pointing in the direction of motion. We present the first 3D hydrodynamic simulations of the formation and evolution of Betelgeuse's bow shock. The models include realistic low temperature cooling and cover a range of plausible interstellar medium densities and stellar velocities between 0.3 - 1.9 cm-3 and 28 - 73 km/s. We show that the flow dynamics and morphology of the bow shock differ substantially due to the preferential growth of Rayleigh-Taylor or Kelvin-Helmholtz instabilities in the models. The former dominate the models with slow stellar velocities resulting in a clumpy bow shock sub-structure, whereas the latter produce a smoother, more layered sub-structure in the fast models. If the mass in the bow shock shell is low, as seems to be implied by the AKARI luminosities (~0.003 Msun), then Betelgeuse's bow shock is very young and is unlikely to have reached a steady state. The circular nature of the bow shock shell is consistent with this conclusion. Thus, our results suggest that Betelgeuse entered the red supergiant phase only recently.