Cometary Nebulas

small (about 1 parsec in diameter) galactic nebulas with continuous emission spectra having, as a rule, the shape of comets. There is usually a young star (T Tauri type) in the head of such a “comet,” and it is this star’s radiation that provides the nebula’s luminescense. Also observed are cometary nebulas having the appearance of two comets directed opposite to the star or of globules with a bright ring in whose center the star is located. It is assumed that cometary nebulas were formed out of specific gas-dust occlusions in diffuse nebulas (“elephant trunks”). After the dissipation of the nebula and the “disappearance” of the hot star that excited it, the occlusion remains, and in its regions of greatest density a young star is formed whose radiation is scattered by the dust and makes the nebula visible.