|
A small interstellar cloud the shape of which bears a superficial resemblance to that of a
comet. A cometary globule is the remnant of a relatively dense condensation within a
cloud of interstellar gas and dust after the more tenuous gas around it has been swept
away by the action of strong ultraviolet radiation from nearby stars. The condensation
becomes the head of the globule and, in its "shadow", some of the material of the
original cloud is protected from the ultraviolet light, giving rise to the comet-like
tail structures.
Cometary globules occur in regions of star formation and it is thought that, over time, they evolve to become Bok globules. About forty are known in the Gum Nebula . The Horsehead Nebula is a cometary globule in the process of formation.
|