Stellar wind

Star wind the continuous stream of material, which extends from the surface of stars. The wind speeds are, depending on the type of star between several tens and several 1000 km / s, the observed mass loss rates range from up solar masses per year.

There are various forms of star winches, which are distinguished by their drive mechanism.

• Winds cool stars, like the one made ​​of red giants from neutral atoms and molecules such as carbon monoxide, silicates, and the like. This dusty winds are only a few tens of km / s relatively slow. The matter is accelerated in the atmosphere of the red giant's by shock waves due to pulsations. At a certain distance from the star, in which the temperature is sufficiently decreased, the gas is condensed into dust. The driving force is the radiation pressure on the molecules of the dust from scattering. The mass loss rates can solar masses per year to be very high up. Such winds occur in the late stages of stellar evolution and are, for example, for the formation of planetary nebulae responsible.

• In solar-like main sequence stars, the wind of charged particles, mostly protons and electrons there. Such winds like the solar wind are mainly driven by the extreme temperatures of the corona of a few million Kelvin. The thereby acting gas pressure accelerates the wind on a few hundred km / s Currently, the sun loses about solar masses per year, you wind therefore has no influence on the development path of the sun. For main sequence stars with an outer Konvektionschicht a corona forms. This thin atmosphere is heated by means of sound waves to several million degrees Kelvin and subsequently the components of the plasma to achieve a movement of heat which is sufficient to allow escape as star wind.

• Winds of hot stars, such as from a surface temperature of 10,000 K, have the same chemical composition as the stellar surface itself Most atoms are ionized in this case one or more times. These winds can a few thousand km / s quickly. Winds of hot stars are also driven by the radiation pressure of the central star, but unlike cool winds he does not act by scattering of the continuous Stern spectrum, but by absorption in spectral lines in the ultraviolet. The mass loss rates range from in main sequence stars over in the supergiant to in Wolf -Rayet stars. The star η Carinae has extreme during a twenty -year outbreak in 1840 lost about half a solar mass per year. The stellar wind of hot stars is highly inhomogeneous. The inhomogeneity can be observed indirectly windakkretierenden X-ray binaries. In this case, the stellar wind from a compact star, a white dwarf, a neutron star or a black hole, captured and transferred via a accretion disk on the star. Upon impact on the surface of a white dwarf or neutron star X-ray radiation is released as thermal radiation, which is directly proportional to the amount of accreted wind. This allows the lumpy structure of the stellar wind of hot star to analyze.

• For some types of stars that accrete material, such as T Tauri stars, a wind can form in the form of a jet. A part of falling on the star material is deflected by a magnetic field and thrown along the polar axis.

While stellar winds in the main sequence stage will not have much influence on the development of the star, the later stages of which are influenced decisively. Many massive stars evolve at the end the only reason to white dwarfs and not explode as a supernova, because they have previously lost sufficient mass.