Bok globule: Difference between revisions

Bok globule
Bok globule
	The Finger of God Globule in the Carina Nebula
Characteristics
Type	Isolated Dark nebulae
Found	HII regions
Mass range	2M☉-50M☉
Chemical composition	Molecular hydrogen, carbon oxides, helium, and silicate dust
Size range	~1ly
External links
	Media category
	Q213936
Additional Information
Discovered	Bart Bok, 1940s

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In astronomy, Bok globules are isolated and relatively small dark nebulae containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about two^[1] to 50 solar masses contained within a region about a light year or so across (about 4.5×10⁴⁷ m³).^[2] They contain molecular hydrogen (H₂), carbon oxides and helium, and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation of double- or multiple-star systems.^[3]

History

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.^[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 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.^[5] Further observations have revealed that some Bok globules contain embedded warm sources,^[2] some contain Herbig–Haro objects,^[6] and some show outflows of molecular gas.^[7] Millimeter-wave emission line studies have provided evidence for the infall of material onto an accreting protostar.^[8] 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.^[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-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).^[11]

Image gallery

Thackeray's Globules, a set of Bok globules in the H II region IC 2944, taken with the WFPC2 instrument on the Hubble Space Telescope
Bok globules located within the NGC 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

^ Michael Szpir (May–June 2001). "Bart Bok's Black Blobs". American Scientist. Archived from the original on 2017-04-24. Retrieved 2008-11-19. Bok globules such as Barnard 68 are only about half a light-year across and weigh in at about two solar masses
^ ^a ^b Clemens, 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 ^b Yun, 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

[1] Michael Szpir (May–June 2001). "Bart Bok's Black Blobs". American Scientist. Archived from the original on 2017-04-24. Retrieved 2008-11-19. Bok globules such as Barnard 68 are only about half a light-year across and weigh in at about two solar masses

[Clemens91-2] Clemens, 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.

[3] 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.

[Bok1947-4] Bok, Bart J.; Reilly, Edith F. (March 1947). "Small Dark Nebulae". Astrophysical Journal. 105: 255. Bibcode:1947ApJ...105..255B. doi:10.1086/144901.

[Yun1990-5] Yun, 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.

[Reipurth1992-6] 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.

[Yun1992-7] 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.

[Zhou1993-8] 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-9] 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-10] 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.

[11] Cometary globules. 1 Formation, evolution and morphology, B. Lefloch and B. Lazareff, 1994.

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@@ Line 1: / Line 1: @@
+{{Short description|Isolated, small, and opaque nebula}}
-{{Star formation}}
+{{Infobox astronomical formation
-In [[astronomy]], '''Bok globules''' are isolated and relatively small [[dark nebula]]e, containing dense [[cosmic dust]] and gas from which [[star formation]] may take place. Bok globules are found within [[H II region]]s, and typically have a [[mass]] of about 2<ref>{{cite web |author=Michael Szpir |title=Bart Bok's Black Blobs |url=http://www.americanscientist.org/template/AssetDetail/assetid/14678 |date=May–June 2001 |archiveurl=https://web.archive.org/web/20030629033609/http://www.americanscientist.org/template/AssetDetail/assetid/14678 |archivedate=2003-06-29 |publisher=[[American Scientist]] |quote=Bok globules such as Barnard 68 are only about half a light-year across and weigh in at about two solar masses |accessdate=2008-11-19}}</ref> to 50 [[solar mass]]es contained within a region about a [[light year]] or so across (about [[Orders of magnitude (one cubic gigametre and greater)|{{val|4.5|e=47|u=m3}}]]).<ref name="Clemens91">{{cite journal
+|name=Bok globule
-| last = Clemens
+|image=File:"Finger of God" Bok globule in the Carina Nebula.jpg
-| first = Dan P.
+|caption=The [[Finger of God Globule]] in the [[Carina Nebula]]
+|where=[[HII regions]]
+|Mass=2{{solar mass}}-50{{solar mass}}
+|size= ~1ly
+|discover= [[Bart Bok]], 1940s
+|comp= [[Molecular hydrogen]], [[carbon oxides]], [[helium]], and [[silicate dust]]
+|thing= Isolated [[Dark nebulae]]
+|commonscat= Bok globules
+|qid=Q213936
+}}{{Star formation}}
+In [[astronomy]], '''Bok globules''' are isolated and relatively small [[dark nebula]]e containing dense [[cosmic dust]] and gas from which [[star formation]] may take place. Bok globules are found within [[H II region]]s, and typically have a [[mass]] of about two<ref>{{cite web |author=Michael Szpir |title=Bart Bok's Black Blobs |url=http://www.americanscientist.org/issues/pub/bart-boks-black-blobs |date=May–June 2001 |publisher=[[American Scientist]] |quote=Bok globules such as Barnard 68 are only about half a light-year across and weigh in at about two solar masses |access-date=2008-11-19 |archive-date=2017-04-24 |archive-url=https://web.archive.org/web/20170424002432/http://www.americanscientist.org/issues/pub/bart-boks-black-blobs  }}</ref> to 50 [[solar mass]]es contained within a region about a [[light year]] or so across (about [[Orders of magnitude (one cubic gigametre and greater)|{{val|4.5|e=47|u=m3}}]]).<ref name="Clemens91">{{cite journal
+| last1 = Clemens
+| first1 = Dan P.
 | last2 = Yun
-| first2 = Joao Lin
+| first2 = João Lin
 | last3 = Meyer
 | first3 = Mark H.
 | date = March 1991
 | title = BOK globules and small molecular clouds – Deep IRAS photometry and (C-12)O spectroscopy
-| url = http://adsabs.harvard.edu/abs/1991ApJS...75..877C
 | journal = Astrophysical Journal Supplement
 | volume = 75
-| pages = 877
+| page = 877
 | bibcode = 1991ApJS...75..877C
 | doi = 10.1086/191552
-}}</ref> They contain [[molecular hydrogen]] (H<sub>2</sub>), [[carbon]] oxides and [[helium]], and around 1% (by mass) of silicate dust.  Bok globules most commonly result in the formation of [[Binary star|double]] or multiple star systems.<ref>{{Cite conference | first = R. | last = Launhardt
+}}</ref> They contain [[molecular hydrogen]] (H<sub>2</sub>), [[carbon]] oxides and [[helium]], and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation of [[Binary star|double]]- or multiple-star systems.<ref>{{Cite conference | first1 = R. | last1 = Launhardt
-| first2 = A.I.
+| first2 = A. I. | last2  = Sargent
+| first3 = T. | last3  = Henning
+| first4 = R. | last4  = Zylka
+| first5 = H. | last5  = Zinnecker
+| title = Binary and multiple star formation in Bok globules | book-title = Birth and Evolution of Binary Stars, Poster Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars | page = 103 | publisher = Bo Reipurth and Hans Zinnecker | date = 10–15 April 2000 | location = Potsdam, Germany | bibcode = 2000IAUS..200P.103L }}</ref>
+== History ==
-| last2  = Sargent
+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 [[cocoon (silk)|cocoons]]" that were undergoing [[gravitational collapse]] to form new stars, from which [[star]]s and [[star cluster]]s were born.<ref name="Bok1947">{{cite journal
+| last1 = Bok | first1 = Bart J.
-| first3 = T.
+| last2 = Reilly | first2 = Edith F.
-| last3  = Henning
-| first4 = R.
-| last4  = Zylka
-| first5 = H.
-| last5  = Zinnecker
-| title = Binary and multiple star formation in Bok globules | booktitle = Birth and Evolution of Binary Stars, Poster Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars | pages = 103 | publisher = Bo Reipurth and Hans Zinnecker | date = 10–15 April 2000 | location = Potsdam, Germany | url = http://adsabs.harvard.edu/abs/2000IAUS..200P.103L | accessdate = 2010-03-29}}</ref>
-Bok globules were first observed by astronomer [[Bart Bok]] in the 1940s. In a paper published in 1947, Bok and E.F. Reilly hypothesized that these clouds were "similar to insect's [[cocoon (silk)|cocoons]]" that were undergoing [[gravitational collapse]] to form new stars from which [[star]]s and [[star cluster]]s were born.<ref name="Bok1947">{{cite journal
-| last = Bok
-| first = Bart J.
-| last2 = Reilly
-| first2 = Edith F.
 | date = March 1947
 | title = Small Dark Nebulae
-| url = http://adsabs.harvard.edu/abs/1947ApJ...105..255B
 | journal = Astrophysical Journal
 | volume = 105
-| pages = 255
+| page = 255
 | bibcode = 1947ApJ...105..255B
 | doi = 10.1086/144901
+}}</ref>{{Failed verification| date= January 2017| reason = The 3-page source discusses issues in finding such ''Small Dark Nebulae'', and lists and describes a number of such in various locations, but does not use the "cocoon" simile or express any part of the stated hypothesis.}}
-}}</ref> 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 spectrum|visible]] light emitted from within it.  An analysis of near [[infrared]] observations published in 1990 confirmed that stars were being born inside Bok globules.<ref name="Yun1990">{{cite journal
+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 spectrum|visible]] light emitted from within it.
-| last       = Yun
-| first      = Joao Lin
+An analysis of near-[[infrared]] observations published in 1990 confirmed that stars were being born inside Bok globules.<ref name="Yun1990">{{cite journal
+| last1       = Yun
+| first1      = João Lin
 | last2      = Clemens
 | first2     = Dan P.
 | date       = December 20, 1990
 | title      = Star formation in small globules – Bart Bok was correct
-| url        = http://adsabs.harvard.edu/abs/1990ApJ...365L..73Y
 | journal    = Astrophysical Journal Letters
 | volume     = 365
@@ Line 58: / Line 61: @@
 | bibcode    = 1990ApJ...365L..73Y
 | doi        = 10.1086/185891
+| doi-access= free
 }}</ref> Further observations have revealed that some Bok globules contain embedded warm sources,<ref name="Clemens91" /> some contain [[Herbig–Haro object]]s,<ref name="Reipurth1992">{{cite journal
-| last       = Reipurth
+| last1       = Reipurth | first1      = Bo
-| first      = Bo
+| last2      = Heathcote | first2     = Steve
-| last2      = Heathcote
+| last3      = Vrba | first3     = Frederick
-| first2     = Steve
-| last3      = Vrba
-| first3     = Frederick
 | date       = March 1992
-| title      = Star formation in Bok globules and low-mass clouds. IV – Herbig-Haro objects in B335
+| title      = Star formation in Bok globules and low-mass clouds. IV – Herbig–Haro objects in B335
-| url        = http://adsabs.harvard.edu/abs/1992A%26A...256..225R
 | journal    = Astronomy & Astrophysics
 | volume     = 256
 | issue      = 1
-| pages      = 225
+| page      = 225
 | bibcode    = 1992A&A...256..225R
-| doi        =
 }}</ref> and some show [[Bipolar outflow|outflows]] of [[Molecular cloud|molecular gas]].<ref name="Yun1992">{{cite journal
-| last       = Yun
+| last1       = Yun
-| first      = Joao Lin
+| first1      = João Lin
 | last2      = Clemens
 | first2     = Dan P.
 | date       = January 1992
 | title      = Discovery of outflows from young stellar objects in BOK globules
-| url        = http://adsabs.harvard.edu/abs/1992ApJ...385L..21Y
 | journal    = Astrophysical Journal Letters
 | volume     = 385
@@ Line 87: / Line 85: @@
 | bibcode    = 1992ApJ...385L..21Y
 | doi        = 10.1086/186268
+| doi-access= free
 }}</ref>  Millimeter-wave [[emission line]] studies have provided evidence for the infall of material onto an accreting [[protostar]].<ref name="Zhou1993">{{cite journal
-| last       = Zhou
+| last1       = Zhou | first1      = Shudong
-| first      = Shudong
+| last2      = Evans | first2     = Neal J. II
-| last2      = Evans
+| last3      = Koempe | first3     = Carsten
-| first2     = Neal J., II
+| last4      = Walmsley | first4     = C. M.
-| last3      = Koempe
-| first3     = Carsten
-| last4      = Walmsley
-| first4     = C.M.
 | date       = March 1993
 | title      = Evidence for protostellar collapse in B335
-| url        = http://adsabs.harvard.edu/abs/1993ApJ...404..232Z
 | journal    = Astrophysical Journal, Part 1
 | volume     = 404
 | issue      = 1
-| pages      = 232
+| page      = 232
 | bibcode    = 1993ApJ...404..232Z
 | doi        = 10.1086/172271
+| s2cid = 120834998
 }}</ref>
+It is now thought that a typical Bok globule contains about 10 [[solar mass]]es 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.<ref name="Yun1990" /><ref name= Clemens>{{cite journal |last=Clemens |first=D. P. |author2= Yun, J. L.|author3= Heyer, M. H. |date=1991 |title=Bok globules and small molecular clouds—Deep IRAS photometry and (C-12)O spectroscopy |journal=Astrophysical Journal Supplement |volume=75 |pages=877–904 | doi=10.1086/191552 |bibcode=1991ApJS...75..877C}}</ref><ref name=Launhardt>{{cite conference |last=Launhardt |first=R. |author2=Sargent, A. I. |author3=Henning, T. |author4=Zylka, R. |author5= Zinnecker, H.  |date=2000 |title=Binary and multiple star formation in Bok globules |book-title=Birth and Evolution of Binary Stars, Poster Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars |editor1=Reipurth, B.|editor2=Zinnecker, H. |page=103 |bibcode=2000IAUS..200P.103L}}</ref>
-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 infrared [[extinction (astronomy)|extinction]] and even star counting in a bid to probe these objects further.
+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-infrared [[extinction (astronomy)|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''').<ref>[http://adsabs.harvard.edu/full/1994A%26A...289..559L Cometary globules. 1 Formation, evolution and morphology], B. Lefloch and B. Lazareff, 1994</ref>
+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''').<ref>[http://adsabs.harvard.edu/full/1994A%26A...289..559L Cometary globules. 1 Formation, evolution and morphology], B. Lefloch and B. Lazareff, 1994.</ref>
 ==Image gallery==
+<gallery mode="packed">
-[[File:Bok globules in IC2944.jpg|thumb|250px|left|An image of [[Thackeray's Globules]], a set of Bok globules in the [[H II region]] [[IC 2944]], taken with the [[Wide Field and Planetary Camera 2|WFPC2]] instrument on the [[Hubble Space Telescope]]]]
+File:Bok globules in IC2944.jpg|[[Thackeray's Globules]], a set of Bok globules in the [[H II region]] [[IC 2944]], taken with the [[Wide Field and Planetary Camera 2|WFPC2]] instrument on the [[Hubble Space Telescope]]
-[[File:NGC 281HSTFull.jpg|thumb|250px|center|Bok globules located within the [[NGC 281]] nebula (IC 1590 cluster).]]
+File:NGC 281HSTFull.jpg|Bok globules located within the [[NGC 281]] nebula (IC 1590 cluster)
+File:Barnard 68.jpg|[[Barnard 68]], at a distance of only 410 light-years, is one of the nearest Bok globules. Its diameter is about {{cvt|12,500|AU|ly}} (≈ 2 trillion km)
+</gallery>
 == See also ==
-{{commons category|Bok_globule|Bok Globule}}
 * [[Molecular cloud]]
-*[[Barnard 68]]
+* [[Barnard 68]]
 * [[CG 4]]
-*[[NGC 281]]
+* [[NGC 281]]
 * [[IC 2944]]
@@ Line 128: / Line 125: @@
 == External links ==
+{{Commons category|Bok globules}}
 * [http://www.universetoday.com/am/publish/star_in_the_making.html A Star in the Making]
+* [https://apod.nasa.gov/apod/ap240521.html Cometary globule CG4] at [[APOD]]
 {{Star}}
+{{Star formation navbox}}
 {{nebula}}
+{{Portal bar|Astronomy|Spaceflight|Outer space|Solar System}}
+{{Authority control}}
 [[Category:Dark nebulae|*Bok globule]]
+[[Category:1940s in science]]

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 Integrated Flux Nebula
Post-stellar nebulae	Planetary nebula Supernova remnant Pulsar wind nebula Supershell
Clouds	Interstellar cloud Molecular cloud Infrared cirrus 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