An Inside Out View of Bubbles

TL;DR

This paper reviews recent observations of stellar wind bubbles in X-ray wavelengths, highlighting discrepancies with models and emphasizing the need for more realistic physics in future theoretical work.

Contribution

It provides a comprehensive overview of X-ray observations of stellar wind bubbles and discusses the implications for modeling their evolution.

Findings

X-ray emission detected from various stellar bubbles and nebulae.

Significant differences between observed and predicted X-ray luminosities.

Hot gas temperatures are generally lower than some models predict.

Abstract

Fast stellar winds can sweep up ambient media and form bubbles. The evolution of a bubble is largely controlled by the content and physical conditions of the shocked fast wind in its interior. This hot gas was not clearly observed until the recent advent of Chandra and XMM-Newton X-ray observatories. To date, diffuse X-ray emission has been unambiguously detected from two circumstellar bubbles blown by WR stars, four planetary nebulae, and two superbubbles blown by young clusters. Model fits to the X-ray spectra show that the circumstellar bubbles are dominated by hot gas with low temperatures (<= 3x10^6 K), while the interstellar bubbles contain significant fractions of hotter gas (>= 5x10^6 K). In all cases, large discrepancies in the X-ray luminosity are found between observations and conventional models of bubbles. Future theoretical models of bubbles need to re-examine the validity of heat conduction and take into account realistic microscopic processes such as mass loading from dense clumps/knots and turbulent mixing. Chandra ACIS-S observation of NGC 6888 will shed light on these astrophysical processes.