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 ( solar masses per year), slow 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 ( solar masses per year) but very high velocities . 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.
G-type stars like the Earth's Sun, have a wind driven by their hot, magnetized corona. The Sun's wind is called the solar wind. These winds consist mostly of high-energy electrons and protons (about 1 keV) 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 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.
Famous quotes containing the word wind:
“I have hardly begun to live on Staten Island yet; but, like the man who, when forbidden to tread on English ground, carried Scottish ground in his boots, I carry Concord ground in my boots and in my hat,—and am I not made of Concord dust? I cannot realize that it is the roar of the sea I hear now, and not the wind in Walden woods. I find more of Concord, after all, in the prospect of the sea, beyond Sandy Hook, than in the fields and woods.”
—Henry David Thoreau (1817–1862)