Stellar-wind bubble is the astronomical term usually used to describe a cavity light years across filled with hot gas blown into the interstellar medium by the high-velocity (several thousand km/s) stellar wind from a single massive star of type O or B. Weaker stellar winds still blow bubble structures though, and these are also called astrospheres. The heliosphere blown by the solar wind, within which all the major planets of the Solar System are embedded, is in fact a small example of a stellar-wind bubble.

Stellar-wind bubbles have a two-shock structure. The freely-expanding stellar wind hits an inner termination shock, where its kinetic energy is thermalized, producing 10⁶ K, X-ray emitting plasma. The hot, high-pressure, shocked wind expands, driving a shock into the surrounding interstellar gas. If the surrounding gas is dense enough (number densities Failed to parse (Missing texvc executable; please see math/README to configure.): n > 0.1 \mbox{ cm}^{-3}

A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.

Different types of stars have different types of stellar winds.

Post-main-sequence stars nearing the ends of their lives often eject large quantities of mass in massive (Failed to parse (Missing texvc executable; please see math/README to configure.): \scriptstyle \dot{M} > 10^{-3}

) winds. These include red giants and supergiants, and asymptotic giant branch stars. These winds are likely to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars.

Massive stars of types O and B have stellar winds with lower mass loss rates (Failed to parse (Missing texvc executable; please see math/README to configure.): \scriptstyle \dot{M} < 10^{-6}

). Such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen. These high-energy stellar winds blow stellar wind bubbles.