An image of Bok globules in the H II region IC 2944, taken with the WFPC2 instrument on the Hubble Space Telescope

A Bok globule is a dark cloud of dense dust and gas in which star formation is taking 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^[1]. 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^[2]. Download high resolution version (746x750, 90 KB)Bok globules in IC2944, as seen by the Hubble Space Telescopes WFPC2. ... Download high resolution version (746x750, 90 KB)Bok globules in IC2944, as seen by the Hubble Space Telescopes WFPC2. ... NGC 604, a giant H II region in the Triangulum Galaxy. ... A Hubble Space Telescope image of the Hubble Deep Field showing the characteristic stairstep composition of WFPC2 images The Wide Field and Planetary Camera 2 (WFPC2) is a camera installed on the Hubble Space Telescope. ... The Hubble Space Telescope is one of the most important telescopes in the history of astronomy. ... Star formation is the process by which gas in molecular clouds gets transformed into stars. ... NGC 604, a giant H II region in the Triangulum Galaxy. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... Molecular hydrogen, H2, is a molecule formed from two atoms of hydrogen. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, p Appearance colorless Atomic mass 4. ... Binary star A binary star system consists of two stars both orbiting around their barycenter. ...

Bok globules were first observed by astronomer Bart Bok in the 1940s. In a paper published in 1947, Bok and E.F. Reilly hypothesised that these clouds were 'cocoons' that were undergoing gravitational collapse to form new stars from which stars and star clusters were born^[3]. 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 infrared observations published in 1990 confirmed that stars were being born inside Bok globules^[4]. Further observations have revealed that some Bok globules contain embedded warm sources^[1], some contain Herbig-Haro objects^[5], and some show outflows of molecular gas^[6]. Millimetre-wave emission line studies have also provided evidence for the infall of material onto an accreting protostar^[7]. Bart Jan Bok ( Hoorn, April 28, 1906 – Tucson, August 5, 1983) was a Dutch-American astronomer. ... Events and trends The 1940s were dominated by World War II, the most destructive armed conflict in history. ... Cocoon has a number of meanings. ... Gravitational collapse in astronomy is the sudden inward fall of a massive body under the influence of the force of gravity. ... The Pleiades star cluster A star is any massive gaseous body in outer space, just like the Sun. ... Globular Cluster M92 in the Hercules constellation. ... The noun spectrum (plural: spectra) has a variety of meanings. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... 1990 is a common year starting on Monday of the Gregorian calendar. ... A Herbig-Haro object is a small patch of nebulosity associated with newly-born stars. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... The protostar period is the period in the evolution of a star after the cloud of hydrogen, helium and dust has started contraction and before the star has reached the main sequence on the Hertzsprung-Russell diagram. ...

See also

• Evaporating gaseous globule
• Giant molecular cloud

A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ...

External links

• Article from American Scientist (May-June 2001)
• A Star in the Making

References

1. Clemens D.P., Yun, J.L., Heyer M.H. (1991). Bok globules and small molecular clouds – Deep IRAS photometry and (C-12)O spectroscopy, Astrophysical Journal Supplement, v.75, p.877
2. Launhardt R., Sargent A.I., Henning T., et al. (2002). Binary and multiple star formation in Bok globules, Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars. Eds Reipurth & Zinnecker, p.103
3. Bok, B. J., Reilly, E. F. (1947). Small Dark Nebulae, Astrophysical Journal, v.105, p.255
4. Yun J.L., Clemens D.P. (1990). Star formation in small globules – Bart Bok was correct, Astrophysical Journal, v.365, p.L73
5. Reipurth, B., Heathcote, S., & Vrba, F. (1992), Star formation in Bok globules and low-mass clouds. IV - Herbig-Haro objects in B335, Astronomy & Astrophysics, v.256, p.225
6. Yun, J. L., & Clemens, D. P. (1992). Discovery of outflows from young stellar objects in BOK globules, Astrophysical Journal, v.385, p.L21
7. Zhou, S., Evans, N. J., II, Kömpe, C., & Walmsley, C. M. (1993). Evidence for protostellar collapse in B335, Astrophysical Journal, v.404, p.232