A huge mass of hot gas whose radiation is provided by
its internal → thermonuclear reactions.
A star represents a → hydrodynamic equilibrium
between two opposing forces, the inward → gravitational force,
which is attempting to make the mass collapse and the pressure
caused by the generation of nuclear energy. Below a certain mass (0.08
→ solar masses),
the central pressures and temperatures are insufficient to trigger
the → hydrogen fusion (→ brown dwarf).
Stars have a variety of masses and sizes.
→ Massive stars are less common than
→ low-mass stars
(→ initial mass function).
→ Star formation results from
→ gravitational collapse of
→ molecular clouds
(→ fragmentation; → pre-stellar core;
→ protostar; → accretion).
After leaving the → main sequence, they
pass through several evolutionary stages (e.g., → red giant,
→ supergiant, → white dwarf,
→ supernova, → neutron star)
depending on their initial masses.
See also: → internal structure of stars;
→ spectral classification;
→ luminosity class;
→ variable star;
→ multiple star.
The term star is sometimes loosely applied to objects that do not comply
with the above specifications, but are evolutionary products of stars, such as
neutron stars and white dwarfs. For ancient civilizations a star was anything
appearing in the night sky, apart from perhaps the Moon.
Etymology (EN): M.E. sterre, O.E. steorra;
cf. O.S. sterro, O.N. stjarna, O.Fris. stera,
Du. ster, O.H.G. sterro, Ger. Stern, Goth. stairno;
cognate with Gk. aster, astron, L. stella
(Fr. étoile, Sp. esterella, It. stella), Bret. sterenn,
Pers. setâré, as below.
Etymology (PE): Setâré, variants star, estâr, estâré, and probably axtar,
→ astro-, (Lori, Laki) âsâra, (Laki) hasâra,
(Tabari) essâra, (Baluci) istâr, (Ossetic) st’aly, (i)sthalu,
(Tâti) usdurâ; Mid.Pers. stârag, stâr; Av. star-; cf.
Skt. stár-, tāra-, tārakā- “star;” akin to
Gk. and L., as above; PIE base *ster- “star.”
