An Etymological Dictionary of Astronomy and Astrophysics

The → minimum mass for an → interstellar cloud below which the → thermal pressure of the gas prevents its → collapse under the force of its own → gravity. It is given by the formula M_J = (π^5/2 / 6) G ^-3/2ρ₀^-1/2c_s³, where G is the → gravitational constant, ρ₀ the initial → density, and c_s the isothermal → sound speed.

It can be approximated to M_J
~ 45 (T_K) ^3/2 (n_cm^-3) ^-1/2 in units of solar masses, where T_K is the temperature in → Kelvin, and n_cm^-3 the gas density per cm³. High density favors collapse, while high temperature favors larger Jeans mass. See also: → thermal Jeans mass, → turbulent Jeans mass.

See also: → Jeans; → mass.