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.
See also: → dust; → grain.
