An Etymological Dictionary of Astronomy and Astrophysics

A physical process which allows a → molecular cloud to decouple from → interstellar magnetic field in order to undergo → gravitational collapse. A cloud of pure molecular gas would form stars very fast through collapse
since neutral matter does not respond to the magnetic field. However, the magnetic
field holds up a collapse because the ions present in the cloud collide with the
neutrals and tie them to the field. The collapse can then only proceed if the
magnetic field can be separated from the gas. In denser molecular cores the ionization degree decreases substantially and therefore neutrals and ions decouple.

See also: → ambipolar; → diffusion.