dâne-ye qobâr (#)
Fr.: grains de poussière
A small, solid flake of → graphite and/or → silicates coated with water ice, found in the → interstellar medium or the → interplanetary medium. Dust grains are irregularly shaped with sizes from microns to Angstroms (→ very small grain; → big grain; → PAH). It is believed that the dust is mainly formed in the cool outer layers of → red giants and dispersed in the interstellar medium. In dense environments, such as → molecular clouds and around → protostars, dust grains grow due to collisions (→ grain growth). Therefore, dust grains in → protostellar disks should be larger than interstellar grains. Dust grains absorb and scatter optical and ultraviolet light and re-radiate in infrared (→ dust emission). Dust acts as a catalyst in the interstellar medium, because molecules form via reactions on the surface of dust grains.
fluffy dust grain
dâne-ye qobâr-e korkvâr
Fr.: grain de poussière duveteux
An aggregate of small particles loosely stuck together. Same as → porous dust grain.
interstellar dust grain
dâne-ye qobâr-e andaraxtari
Fr.: grain de poussière interstellaire
→ dust grain.
porous dust grain
dâne-ye qobâr-e porlik
Fr.: grain de poussière poreux
A type of → interstellar dust grain made up of an aggregate of components with a hollow structure. Various processes operating in interstellar and → circumstellar media are believed to produce inhomogeneous and porous dust grains. Porous grains can produce more → extinction per unit mass than their combined individual dust components. They are generally cooler than compact grains (see, e.g., Iati et al. 2001, MNRAS 322, 749).