Magnetically Confined Wind Shocks in X-rays - a Review

TL;DR

This review discusses how magnetic fields in massive stars confine stellar winds, leading to shocks that produce X-rays, highlighting recent observational and theoretical advances in understanding these phenomena.

Contribution

It synthesizes recent observational data and theoretical models on magnetically confined wind shocks in massive stars, emphasizing new insights and future prospects.

Findings

Magnetic confinement leads to X-ray emitting shocks in massive stars.

Recent X-ray observations have characterized hot plasma properties.

Advances in MHD modeling explain shock dynamics and emission features.

Abstract

A subset (~ 10%) of massive stars present strong, globally ordered (mostly dipolar) magnetic fields. The trapping and channeling of their stellar winds in closed magnetic loops leads to magnetically confined wind shocks (MCWS), with pre-shock flow speeds that are some fraction of the wind terminal speed. These shocks generate hot plasma, a source of X-rays. In the last decade, several developments took place, notably the determination of the hot plasma properties for a large sample of objects using XMM-Newton and Chandra, as well as fully self-consistent MHD modelling and the identification of shock retreat effects in weak winds. Despite a few exceptions, the combination of magnetic confinement, shock retreat and rotation effects seems to be able to account for X-ray emission in massive OB stars. Here we review these new observational and theoretical aspects of this X-ray emission and envisage some perspectives for the next generation of X-ray observatories.