Circumstellar medium

The circumstellar medium is gas and dust surrounding a star. Its structure and composition reflect the star’s mass loss and interactions with its environment.

Stellar wind: A flow of charged particles expelled from a star into surrounding space. It carries stellar material outward and helps set the medium’s density and shape.
Asymptotic giant branch: A late evolutionary phase of low- and intermediate-mass stars with a cool, luminous atmosphere and strong mass loss. Its dense winds are a major source of circumstellar gas and dust.
Stellar mass loss: The loss of material from a star through winds, eruptions, or other outflows. Circumstellar gas and dust preserve evidence of this transfer from star to space.
Betelgeuse: A nearby red supergiant in the constellation Orion, known for variability and substantial mass loss. Its asymmetric surrounding material records changing outflows from a massive evolved star.
Radiation pressure: The force exerted when electromagnetic radiation transfers momentum to matter. It can push dust grains outward from luminous stars.
Red supergiant: A massive, evolved star with an extended, cool atmosphere. Its powerful mass loss builds a substantial surrounding envelope.
Circumstellar dust: Solid grains surrounding a star, produced by condensation or captured from nearby material. Its thermal emission and extinction make it observable across multiple wavelengths.
Mira: A pulsating red giant in the constellation Cetus and the prototype of Mira variable stars. Its long trailing wake shows how circumstellar ejecta interact with interstellar gas.
Dust formation: The process by which solid particles condense from gas in space. Cooling ejecta from evolved stars can condense into circumstellar dust.
Planetary nebula formation: The ejection and ionization of a low- or intermediate-mass star’s outer layers near the end of its life. It transforms an earlier outflow into an expanding, luminous nebula.

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