Stellar Wind

Fast continuous outflow of material (p+, e–, and atoms of heavier metals) ejected from stars. Stellar winds are characterized by speeds of 20–2,000 km/sec. The causes, ejection rates and speeds of stellar winds vary with the mass of the star. In relatively cool, low-mass stars, such as the Sun, the wind is caused by the extremely high temperature (106s K) of the corona. This high temperature probably results from interactions between magnetic fields at the star’s surface, and gives the coronal gas sufficient energy to escape the gravitational attraction of the star. These stars eject only a tiny fraction of their mass per year as a stellar wind but this still represents losses of millions of tonnes of material each second. Over their entire lifetime, stars like our Sun lose only a tiny fraction of 1% of their mass through stellar winds.

In contrast, hot, massive stars can produce stellar winds ~109 times stronger than those of low-mass stars and over their short lifetimes, they can eject up to 50% of their initial mass as 2,000 km/sec winds. These stellar winds are driven directly by radiation pressure from photons escaping the star. In some cases, high-mass stars can eject virtually all of their outer envelopes in winds. The result is a Wolf-Rayet star. Stellar winds play an important part in the chemical evolution of the Universe, as they carry dust and metals back into the interstellar medium where they will be incorporated into the next generation of stars.