X-Raying the Winds of Massive Stars Using High Mass X-Ray Binaries

We are made of stardust—or, at least in significant parts, of material processed in stars. Hot, massive giant stars can drive the chemical evolution of galaxies and trigger and quench star formation through their strong winds and their final demise as supernovae. Yet optical and X-ray measurements of the wind mass loss strongly disagree and can only be reconciled if the winds are highly structured, with colder, dense clumps embedded in a tenuous hot gas. In (quasi-)single stars, however, wind properties are inferred for the whole wind ensemble only; no measurements of individual clumps or clump groups are possible, limiting our understanding of wind properties and launching and therefore of massive stars themselves. Luckily, nature provides us with perfect laboratories to study clumpy winds: high mass X-ray binaries. The radiation from close to the compact object is quasi-point like and effectively X-rays the wind, in particular the clumps crossing our line of sight.

In this talk, I will discuss how we can use a variety of observations to constrain the wind properties in bright high mass X-ray binaries in particular focussing in advances from recent ears as done by the X-wind collaboration. Time- and absorption-resolved high resolution X-ray spectroscopy reveals the composition of the multicomponent wind plasma, the structure of the accretion wake, and the wind's response to changes in irradiation. New simulations of wind accretion pave the way towards constraining clump properties from stochastic variability of absorption.  Future X-ray telescopes such as the recently launched XRISM and upcoming NewAthena will revolutionise the field, allowing us to observe individual clumps in bright sources and, for the first time, make faint sources accessible for high resolution spectroscopy.