Dark nebula: Difference between revisions
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A '''dark nebula''' or '''absorption nebula''' is a type of [[interstellar cloud]], particularly [[molecular cloud]]s, that is so dense that it obscures the [[Visible spectrum|visible wavelengths]] of [[light]] from objects behind it, such as background stars and [[emission nebula|emission]] or [[reflection nebula|reflection]] nebulae. The [[extinction (astronomy)|extinction]] of the light is caused by [[cosmic dust|interstellar dust]] grains in the coldest, densest parts of molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called [[Bok globule]]s. Like other interstellar dust or material, the things it obscures are visible only using [[radio waves]] in [[radio astronomy]] or [[infrared]] in [[infrared astronomy]]. | A '''dark nebula''' or '''absorption nebula''' is a type of [[interstellar cloud]], particularly [[molecular cloud]]s, that is so dense that it obscures the [[Visible spectrum|visible wavelengths]] of [[light]] from objects behind it, such as background stars and [[emission nebula|emission]] or [[reflection nebula|reflection]] nebulae. The [[extinction (astronomy)|extinction]] of the light is caused by [[cosmic dust|interstellar dust]] grains in the coldest, densest parts of molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called [[Bok globule]]s. Like other interstellar dust or material, the things it obscures are visible only using [[radio waves]] in [[radio astronomy]] or [[infrared]] in [[infrared astronomy]]. | ||
Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen [[carbon monoxide]] and nitrogen, which effectively block the passage of light at visible wavelengths. Also present are molecular hydrogen, atomic helium, C<sup>18</sup>O (CO with [[oxygen]] as the [[Oxygen-18|<sup>18</sup>O isotope]]), CS, NH<sub>3</sub> ([[ammonia]]), H<sub>2</sub>CO ([[formaldehyde]]), c-C<sub>3</sub>H<sub>2</sub> ([[cyclopropenylidene]]) and a molecular ion N<sub>2</sub>H<sup>+</sup> ([[diazenylium]]), all of which are relatively transparent. <ref>{{Cite journal|last1=Di Francesco|first1=James|last2=Hogerheijde|first2=Michiel R.|last3=Welch|first3=William J.|last4=Bergin|first4=Edwin A.|date=November 2002|title=Abundances of Molecular Species in Bernard 68|journal=[[The Astrophysical Journal]]|volume=124|issue=5|pages=2749–2755|arxiv=astro-ph/0208298|bibcode=2002AJ....124.2749D|doi=10.1086/344078|s2cid=119078546}}</ref><ref>[http://www.eso.org/public/outreach/press-rel/pr-1999/phot-29-99.html ESO - eso9934 - Secrets of a Dark Cloud] {{webarchive|url=https://web.archive.org/web/20090204200348/http://eso.org/public/outreach/press-rel/pr-1999/phot-29-99.html |date=2009-02-04 }}</ref> | Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen [[carbon monoxide]] and nitrogen, which effectively block the passage of light at visible wavelengths. Also present are molecular hydrogen, atomic helium, C<sup>18</sup>O (CO with [[oxygen]] as the [[Oxygen-18|<sup>18</sup>O isotope]]), CS, NH<sub>3</sub> ([[ammonia]]), H<sub>2</sub>CO ([[formaldehyde]]), c-C<sub>3</sub>H<sub>2</sub> ([[cyclopropenylidene]]) and a molecular ion N<sub>2</sub>H<sup>+</sup> ([[diazenylium]]), all of which are relatively transparent.<ref>{{Cite journal|last1=Di Francesco|first1=James|last2=Hogerheijde|first2=Michiel R.|last3=Welch|first3=William J.|last4=Bergin|first4=Edwin A.|date=November 2002|title=Abundances of Molecular Species in Bernard 68|journal=[[The Astrophysical Journal]]|volume=124|issue=5|pages=2749–2755|arxiv=astro-ph/0208298|bibcode=2002AJ....124.2749D|doi=10.1086/344078|s2cid=119078546}}</ref><ref>[http://www.eso.org/public/outreach/press-rel/pr-1999/phot-29-99.html ESO - eso9934 - Secrets of a Dark Cloud] {{webarchive|url=https://web.archive.org/web/20090204200348/http://eso.org/public/outreach/press-rel/pr-1999/phot-29-99.html |date=2009-02-04 }}</ref> | ||
The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The closest and largest dark nebulae are visible to the naked eye, since they are the least obscured by stars in between Earth and the nebula, and because they have the largest [[angular size]], appearing as dark patches against the brighter background of the [[Milky Way]] like the [[Coalsack Nebula]] and the [[Great Rift (astronomy)|Great Rift]]. These naked-eye objects are sometimes known as [[Constellation#Dark cloud constellations|dark cloud constellations]] and take on a variety of names. | The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The closest and largest dark nebulae are visible to the naked eye, since they are the least obscured by stars in between Earth and the nebula, and because they have the largest [[angular size]], appearing as dark patches against the brighter background of the [[Milky Way]] like the [[Coalsack Nebula]] and the [[Great Rift (astronomy)|Great Rift]]. These naked-eye objects are sometimes known as [[Constellation#Dark cloud constellations|dark cloud constellations]] and take on a variety of names. | ||
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Dark nebula form in the night sky apparent [[dark cloud constellation]]s. | Dark nebula form in the night sky apparent [[dark cloud constellation]]s. | ||
{{excerpt|Constellation#List of dark cloud constellations}} | {{excerpt|Constellation#List of dark cloud constellations}} | ||
[[File:Milkyway360-hemispheres-32k m14-g1 Clouds.jpg|thumb|650x650px|The Milky Way as seen by Gaia, with prominent dark features labeled in white, as well as prominent [[star cloud]]s labeled in black|center]] | [[File:Milkyway360-hemispheres-32k m14-g1 Clouds.jpg|thumb|650x650px|The Milky Way as seen by ''[[Gaia (spacecraft)|Gaia]]'', with prominent dark features labeled in white, as well as prominent [[star cloud]]s labeled in black|center]] | ||
[[File:Regioni_celesti_scelte_-_Osc_A.png|thumb|650x650px|Main dark nebulae of the [[solar apex]] half of the [[galactic plane]]|center]] | [[File:Regioni_celesti_scelte_-_Osc_A.png|thumb|650x650px|Main dark nebulae of the [[solar apex]] half of the [[galactic plane]]|center]] | ||
[[File:Regioni_celesti_scelte_-_Osc_B.png|thumb|650x650px|Main dark nebulae of the [[solar antapex]] half of the galactic plane|center]] | [[File:Regioni_celesti_scelte_-_Osc_B.png|thumb|650x650px|Main dark nebulae of the [[solar antapex]] half of the galactic plane|center]] | ||
[[File:Dust poster.png|thumb|Dust extinction within 1250 pc]] | |||
== See also == | == See also == | ||
* [[List of dark nebulae]] | * [[List of dark nebulae]] | ||
* [[Bok globule]] | * [[Bok globule]] | ||
* [[Infrared dark cloud]] | |||
* [[Dark Cloud (disambiguation)]] | * [[Dark Cloud (disambiguation)]] | ||
Latest revision as of 13:58, 2 October 2025
Template:Short descriptionScript error: No such module "other uses".Template:More citations needed
Template:Star formation A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains in the coldest, densest parts of molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. Like other interstellar dust or material, the things it obscures are visible only using radio waves in radio astronomy or infrared in infrared astronomy.
Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen carbon monoxide and nitrogen, which effectively block the passage of light at visible wavelengths. Also present are molecular hydrogen, atomic helium, C18O (CO with oxygen as the 18O isotope), CS, NH3 (ammonia), H2CO (formaldehyde), c-C3H2 (cyclopropenylidene) and a molecular ion N2H+ (diazenylium), all of which are relatively transparent.[1][2]
The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The closest and largest dark nebulae are visible to the naked eye, since they are the least obscured by stars in between Earth and the nebula, and because they have the largest angular size, appearing as dark patches against the brighter background of the Milky Way like the Coalsack Nebula and the Great Rift. These naked-eye objects are sometimes known as dark cloud constellations and take on a variety of names.
In the inner molecular regions of dark nebulae, events such as the formation of stars and masers take place.
Complexes and constellations
Along with molecular clouds, dark nebula make up molecular cloud complexes.
Dark nebula form in the night sky apparent dark cloud constellations. Template:Excerpt
See also
References
Template:Nebula Template:Star formation navbox Template:Portal bar Template:Authority control
- ↑ Script error: No such module "Citation/CS1".
- ↑ ESO - eso9934 - Secrets of a Dark Cloud Template:Webarchive