An Etymological Dictionary of Astronomy and Astrophysics

In models of star formation, an isothermal sphere in which the density distribution in the static or nearly static outer envelope obeys an r^-2 power law. In the limit of infinite central concentration, the unstable equilibrium approaches the singular isothermal sphere which has the density and mass distributions ρ(r) = (a²/2πG)r^-2 and M(r) = (2a²/G)r, where a is the isothermal → sound speed inside the cloud, G is the → gravitational constant, and r the distance from the center (F. H. Shu, 1977, ApJ 214, 488).

See also: → singular; → isothermal; → sphere.