A stellar wind is a flow of 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. These include red giants and supergiants, and asymptotic giant branch stars.
These winds are understood to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars. Massive stars of Class O and B have stellar winds with lower mass loss rates but very high velocities (v > 1-2000 km/s).
These high-energy stellar winds blow stellar wind bubbles. Class G stars like the Earth’s Sun have a wind driven by their hot, magnetized corona. The Sun’s wind is called the solar wind.
The solar winds flow outward supersonically at varying speeds depending on their origin reaching up to around one million miles per hour to great distances, filling a region known as the heliosphere, an enormous bubble-like volume surrounded by the interstellar medium.
Other related phenomena include the aurora (northern and southern lights), the plasma tails of comets that always point away from the Sun, and geomagnetic storms that can change the direction of magnetic field lines.
These winds consist mostly of high-energy electrons and protons that are able to escape the star’s gravity because of the high temperature of the corona. Stellar winds from main-sequence stars do not strongly influence the evolution of lower mass stars such as the Sun.
However, for more massive stars such as Class O stars, the mass loss can result in a star shedding as much as 50% of its mass whilst on the main sequence: this clearly has a significant impact on the later stages of evolution.
The influence can even be seen for intermediate mass stars, which will become white dwarfs at the ends of their lives rather than exploding as supernovae only because they lost enough mass in their winds.