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Bok globule

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Isolated, small, and opaque nebula

Bok globule
TheFinger of God Globule in theCarina Nebula
Characteristics
Type	IsolatedDark nebulae
Found	HII regions
Mass range	2`M`_☉-50`M`_☉
Chemical composition	Molecular hydrogen,carbon oxides,helium, andsilicate dust
Size range	~1ly
External links
Media category
Q213936
Additional Information
Discovered	Bart Bok, 1940s

Star formation

Object classes
Interstellar medium Molecular cloud Bok globule Dark nebula Young stellar object Protostar Pre-main-sequence star T Tauri star Herbig Ae/Be star Herbig–Haro object
Theoretical concepts
Accretion Initial mass function Jeans instability Kelvin–Helmholtz mechanism Nebular hypothesis Planetary migration
v t e

Inastronomy,Bok globules are isolated and relatively smalldark nebulae containing densecosmic dust and gas from whichstar formation may take place. Bok globules are found withinH II regions, and typically have amass of about two^[1] to 50solar masses contained within a region about alight year or so across (about4.5×10⁴⁷ m³).^[2] They containmolecular hydrogen (H₂),carbon oxides andhelium, and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation ofdouble- or multiple-star systems.^[3]

History

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Bok globules were first observed by astronomerBart Bok in the 1940s. In an article published in 1947, he andEdith F. Reilly hypothesized that these clouds were "similar to insect'scocoons" that were undergoinggravitational collapse to form new stars, from whichstars andstar clusters were born.^[4]^{[failed verification]} This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured allvisible light emitted from within it.

An analysis of near-infrared observations published in 1990 confirmed that stars were being born inside Bok globules.^[5] Further observations have revealed that some Bok globules contain embedded warm sources,^[2] some containHerbig–Haro objects,^[6] and some showoutflows ofmolecular gas.^[7] Millimeter-waveemission line studies have provided evidence for the infall of material onto an accretingprotostar.^[8]It is now thought that a typical Bok globule contains about 10solar 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.^[5]^[9]^[10]

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 remains somewhat a mystery. Methods applied so far have relied on column density derived from near-infraredextinction 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).^[11]

Image gallery

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Thackeray's Globules, a set of Bok globules in theH II region IC 2944, taken with theWFPC2 instrument on theHubble Space Telescope
Bok globules located within theNGC 281 nebula (IC 1590 cluster)
Barnard 68, at a distance of only 410 light-years, is one of the nearest Bok globules. Its diameter is about 12,500 AU (0.198 ly) (≈ 2 trillion km)

References

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^Michael Szpir (May–June 2001)."Bart Bok's Black Blobs".American Scientist. Archived fromthe original on 2017-04-24. Retrieved2008-11-19.Bok globules such as Barnard 68 are only about half a light-year across and weigh in at about two solar masses
^^a ^bClemens, Dan P.; Yun, João Lin; Meyer, Mark H. (March 1991). "BOK globules and small molecular clouds – Deep IRAS photometry and (C-12)O spectroscopy".Astrophysical Journal Supplement.75: 877.Bibcode:1991ApJS...75..877C.doi:10.1086/191552.
^Launhardt, R.; Sargent, A. I.; Henning, T.; Zylka, R.; Zinnecker, H. (10–15 April 2000). "Binary and multiple star formation in Bok globules".Birth and Evolution of Binary Stars, Poster Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars. Potsdam, Germany: Bo Reipurth and Hans Zinnecker. p. 103.Bibcode:2000IAUS..200P.103L.
^Bok, Bart J.; Reilly, Edith F. (March 1947). "Small Dark Nebulae".Astrophysical Journal.105: 255.Bibcode:1947ApJ...105..255B.doi:10.1086/144901.
^^a ^bYun, João Lin; Clemens, Dan P. (December 20, 1990)."Star formation in small globules – Bart Bok was correct".Astrophysical Journal Letters.365: L73.Bibcode:1990ApJ...365L..73Y.doi:10.1086/185891.
^Reipurth, Bo; Heathcote, Steve; Vrba, Frederick (March 1992). "Star formation in Bok globules and low-mass clouds. IV – Herbig–Haro objects in B335".Astronomy & Astrophysics.256 (1): 225.Bibcode:1992A&A...256..225R.
^Yun, João Lin; Clemens, Dan P. (January 1992)."Discovery of outflows from young stellar objects in BOK globules".Astrophysical Journal Letters.385: L21.Bibcode:1992ApJ...385L..21Y.doi:10.1086/186268.
^Zhou, Shudong; Evans, Neal J. II; Koempe, Carsten; Walmsley, C. M. (March 1993). "Evidence for protostellar collapse in B335".Astrophysical Journal, Part 1.404 (1): 232.Bibcode:1993ApJ...404..232Z.doi:10.1086/172271.S2CID 120834998.
^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.75:877–904.Bibcode:1991ApJS...75..877C.doi:10.1086/191552.
^Launhardt, R.; Sargent, A. I.; Henning, T.; Zylka, R.; Zinnecker, H. (2000). "Binary and multiple star formation in Bok globules". In Reipurth, B.; Zinnecker, H. (eds.).Birth and Evolution of Binary Stars, Poster Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars. p. 103.Bibcode:2000IAUS..200P.103L.
^Cometary globules. 1 Formation, evolution and morphology, B. Lefloch and B. Lazareff, 1994.

External links

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Wikimedia Commons has media related toBok globules.

Stars

List

Formation

Evolution

Classification

Early Late Main sequence O B A F G K M Subdwarf O B WR OB Subgiant Giant Blue Red Yellow Bright giant Supergiant Blue Red Yellow Hypergiant Yellow Carbon S CN CH White dwarf Chemically peculiar Am Ap/Bp CEMP HgMn He-weak Barium Lambda Boötis Lead Technetium Be Shell B[e] Helium Extreme Blue straggler
Remnants	Compact star White dwarf Helium planet Neutron Radio-quiet Pulsar Binary X-ray Magnetar Black hole Stellar black hole Supermassive black hole X-ray binary Burster SGR
Hypothetical	Blue dwarf Black dwarf Exotic Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Quasi-star Gravastar Thorne–Żytkow object Iron Blitzar White hole

Nucleosynthesis

Structure

Properties

Star systems

Earth-centric
observations

Lists

v t e Star formation
Object classes	Interstellar medium Molecular cloud Bok globule Dark nebula Young stellar object Protostar T Tauri star Pre-main-sequence star Herbig Ae/Be star Herbig–Haro object
Theoretical concepts	Initial mass function Jeans instability Kelvin–Helmholtz mechanism Nebular hypothesis Planetary migration
Category Stars portal Commons

v t e Nebulae
Visible nebula	Dark nebula Diffuse nebula Emission nebula Planetary nebula Supernova remnant Nova remnant H II region Reflection nebula Variable nebula Protoplanetary nebula
Pre-stellar nebulae	Giant molecular cloud Bok globule Evaporating gaseous globule Solar nebula
Stellar nebula	Nova remnant Protoplanetary nebula Wolf–Rayet nebula
Post-stellar nebulae	Planetary nebula Supernova remnant Pulsar wind nebula Supershell
Clouds	Interstellar cloud Molecular cloud Infrared cirrus Integrated Flux Nebula High-velocity cloud H I region
Morphology	Bipolar nebula Pinwheel nebula
Intergalactic blobs	Lyman-alpha blob
Lists	Diffuse Largest Nebulae Planetary (PNe) Protoplanetary (PPNe) Supernova remnants (SNRs)
Related	Cometary knot
Category Commons Wiktionary