Bok globule

A Bok globule is a dark cloud of dense dust and gas in which star formation sometimes takes place. Bok globules are found within H II regions, and typically have a mass of about 10–50  solar masses contained within a region about a light year or so across. They contain molecular hydrogen (H2), carbon oxides and helium, and around 1% (by mass) of silicate dust. Bok globules most commonly result in the formation of double or multiple star systems.
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Spherical dark nebulae which are believed to be regions of interstellar clouds, undergoing gravitational collapse. They appear as round clouds which are silhouetted by background stars or emission nebulae. They consist predominantly of gas, although they do have a dust component. The temperature of these globules is usually about 10 - 15 degrees Kelvin, which is sufficiently low for the kinetic energy of the gas particles not to resist the collapse. As the globule collapses, it breaks up and then the fragments, in turn, collapse into protostars. Bok globules vary in the mass they contain from a fraction of a solar mass to several hundred solar masses. They are named after Bart Bok, a Dutch astronomer who first observed the less massive variety earlier this century.