Bok globules were first observed by astronomer
Bart Bok in the 1940s. In an article published in 1947, he and
Edith F. Reilly hypothesized that these clouds were "similar to insect's
cocoons" that were undergoing
gravitational collapse to form new stars, from which
stars and
star clusters were born. This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured all
visible light emitted from within it. An analysis of near-
infrared observations published in 1990 confirmed that stars were being born inside Bok globules. Further observations have revealed that some Bok globules contain embedded warm sources, and some show
outflows of
molecular gas. Millimeter-wave
emission line studies have provided evidence for the infall of material onto an accreting
protostar. It is now thought that a typical Bok globule contains about 10
solar masses of material in a region about a light-year or so across, and that Bok globules most commonly result in the formation of double- or multiple-star systems. Bok globules are still a subject of intense research. Known to be some of the coldest objects in the natural universe, their structure and density remain something of a mystery. Methods applied so far have relied on column density derived from near-infrared
extinction and even star counting in a bid to probe these objects further. Bok globules that are irradiated by ultraviolet light from hot nearby stars exhibit stripping of materials to produce a tail. These types are called "
cometary globules" (
CG). ==Image gallery==