Dark nebula
From Wikipedia, the free encyclopedia
A dark nebula is a type of interstellar cloud that is so dense that it obscures the light from the background emission or reflection nebula (eg. the Horsehead Nebula) or if they block out background stars (eg. the Coalsack Nebula).
The extinction of the light is caused by intersellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulea are associated with Giant Molecular Clouds. Isolated small dark nebulea are called Bok globules.
The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The largest dark nebulae are visible to the naked eye, appearing as dark patches against the brighter background of the Milky Way.
In the inner regions of dark nebulae important events take place, such as the formation of stars and masers.
