Stellar wind

Stellar wind

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 (dot{M} > 10^{-3} solar masses per year), slow (v = 10 mbox{ km s}^{-1}) 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.

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. 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.

Massive stars of types O and B have stellar winds with lower mass loss rates (dot{M} < 10^{-6} solar masses per year) but very high velocities (v > 1-2000mbox{ km s}^{-1}). Such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen. [cite journal| url=| last= Castor| first=J.| coauthors=Abbott, D. C., &amp; Klein, R. I.| title=Radiation-driven winds in Of stars| year=1975| journal=Astrophys. J.| volume=195| pages=157–174| doi=10.1086/153315] These high-energy stellar winds blow stellar wind bubbles.

Although stellar winds from main sequence stars do not strongly influence the evolution of the stars, during the later, post-main sequence phase, mass lost by stellar winds can decide the fate of the star. Many intermediate mass stars become white dwarfs at the ends of their lives rather than exploding as supernovae only because they lost enough mass in their winds.

See also

* Solar wind


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