The Jeans length is the critical size of a gas cloud, of a given temperature and density, above which the cloud must collapse under its own gravity. Below this size, the cloud's internal pressure is enough to resist collapse. The Jean's length, named after James Jeans, is given by
r = √(15kT / 2πdGm)
where k is Boltzmann's constant, T is temperature, d is density, G is the constant
of gravitation and, m is mass.
The Jeans mass is he critical mass a volume of space must contain before it will collapse under the force of its own gravity.