Cometary Astropause of Mira Revealed in the Far-Infrared

TL;DR

This study uses far-infrared imaging to spatially resolve Mira's astropause, revealing its structure, size, and shock dynamics, thus confirming theoretical models of stellar wind-ISM interactions.

Contribution

First direct imaging of Mira's astropause in the far-infrared, providing detailed structural and dynamical insights into stellar wind interactions with the ISM.

Findings

Resolved the contact surface and termination shock of Mira's astropause.

Estimated the age of the astropause to be about 40,000 years.

Confirmed theoretical predictions of shock re-establishment time in the Local Bubble.

Abstract

Evolved mass-losing stars such as Mira enrich the interstellar medium (ISM) significantly by their dust-rich molecular wind. When these stars move fast enough relative to the ISM, the interaction between the wind and ISM generates the structure known as the astropause (a stellar analog of the heliopause), which is a cometary stellar wind cavity bounded by the contact discontinuity surface between the wind and ISM. Far-infrared observations of Mira spatially resolve the structure of its astropause for the first time, distinguishing the contact surface between Mira's wind and the ISM and the termination shock due to Mira's wind colliding with the ISM. The physical size of the astropause and the estimated speed of the termination shock suggest the age of the astropause to be about 40,000 yr, confirming a theoretical prediction of the shock re-establishment time after Mira has entered the Local Bubble.