Stellar wind
Encyclopedia
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 outflow
s 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
star
s nearing the ends of their lives often eject large quantities of mass in massive (
solar masses per year), slow (
) winds. These include red giant
s 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 bubble
s.
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 proton
s (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
star
s 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 dwarf
s at the ends of their lives rather than exploding as supernova
e only because they lost enough mass in their winds.
Stellar atmosphere
The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone. It is divided into several regions of distinct character:...
of a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
. It is distinguished from the bipolar outflow
Bipolar outflow
A bipolar outflow represents two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars , or with evolved post-AGB stars ....
s characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.
Different types
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
of stars have different types of stellar winds.
Post-main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s nearing the ends of their lives often eject large quantities of mass in massive (
solar masses per year), slow () winds. These include red giantRed giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
s and supergiants, and asymptotic giant branch
Asymptotic Giant Branch
The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives....
stars. These winds are likely to be driven by radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
on dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
condensing in the upper atmosphere of the stars.
Massive stars of types
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
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 bubbleStellar wind bubble
Stellar-wind bubble is the astronomical term usually used to describe a cavity light years across filled with hot gas blown into the interstellar medium by the high-velocity stellar wind from a single massive star of type O or B. Weaker stellar winds still blow bubble structures though, and these...
s.
G type stars like the Earth's
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, have a wind driven by their hot, magnetized corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
. The Sun's wind is called the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
. These winds consist mostly of high-energy electrons and proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s (about 1 keV) that are able to escape the star's gravity because of the high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of the corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
.
Stellar winds from main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s 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 dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s at the ends of their lives rather than exploding as supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
e only because they lost enough mass in their winds.