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 sometimes 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. ... The factual accuracy of this article is disputed. ... 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 (HST) is a telescope in orbit around the Earth. ... Star formation is the process by which gas in molecular clouds change into the ball of plasma we call a star. ... NGC 604, a giant H II region in the Triangulum Galaxy. ... Mass is a property of a physical object that quantifies the amount of matter and energy it contains. ... 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, s Appearance colorless Atomic mass 4. ... Artists impression of a binary star system consisting of a black hole, with an accretion disc around it, and a main sequence star. ...

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 near 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 World War II was a truly global conflict with many facets: immense human suffering, fierce indoctrination, and the use of new, extremely devastating weapons such as the atomic bomb. ... Cocoon has a number of meanings. ... This article or section does not cite its references or sources. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... Globular Cluster M92 in the Hercules constellation. ... The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of wavelengths that are studied in the field of optics. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... This article is about the year. ... Herbig-Haro object HH47, imaged by the Hubble Space Telescope. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... 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. ... Protostar is a period after clouds of hydrogen, helium and dust begin to contract and before the star reaches the main sequence. ...

Bok globules are still a subject of intense research. Known to be some of the coldest objects in the natural universe (as cold as 3 kelvins) their structure and density remains somewhat 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. The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ...

See also

• Evaporating gaseous globule
• Giant molecular cloud
• Thackeray's Globules

A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ... Thackerays Globules are dense, opaque dust clouds in outer space, known as globules, in the star-forming region IC 2944. ...

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