A

David

Darling

gas-bounded nebula

A gas-bounded nebula is an interstellar cloud that is kept more-or-less completely ionized by one or more hot, luminous stars within it. The visible extent of the nebula is thus limited by the actual size of the cloud and the quantity of material it contains, rather than in the case of a radiation-bounded nebula, where the limiting factor is the amount of ionizing radiation available.