Dark nebula

The dark nebula LDN 1768 in front of background stars

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

* Accretion
* Initial mass function
* Jeans instability
* Kelvin–Helmholtz mechanism
* Nebular hypothesis
* Planetary migration

* v
* t
* e

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 located 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, things it obscures are only visible 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. These clouds are the spawning grounds of stars and planets, and understanding their development is essential to understanding star formation.[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, important events take place, such as the formation of stars and masers.

## 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.

This section is an excerpt from Constellation#List of dark cloud constellations[ edit ]

The Milky Way as seen by Gaia, with prominent dark features labeled in white, as well as prominent star clouds labeled in black.

Main dark nebulae of the solar apex half of the galactic plane.

Main dark nebulae of the solar antapex half of the galactic plane.

## See also

* List of dark nebulae
* Bok globule
* Dark Cloud (disambiguation)

## References

1. ↑ Di Francesco, James; Hogerheijde, Michiel R.; Welch, William J.; Bergin, Edwin A. (November 2002). "Abundances of Molecular Species in Bernard 68". The Astrophysical Journal 124 (5): 2749–2755. doi:10.1086/344078. Bibcode: 2002AJ....124.2749D.
2. ↑ ESO - eso9934 - Secrets of a Dark Cloud

* v
* t
* e

Nebula

Visible nebula|

* Dark nebula
* Diffuse nebula
* Emission nebula
* Planetary nebula
* Supernova remnant
* Nova remnant
* H II region
* Reflection nebula
* Variable nebula
* Preplanetary nebula

Pre-stellar nebula|

* Giant molecular cloud
* Bok globule
* Evaporating gaseous globule
* Solar nebula

Stellar nebula|

* Nova remnant
* Protoplanetary nebula
* Wolf–Rayet nebula

Post-stellar nebula|

* 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

Lists|

* Diffuse
* Planetary (PNe)
* Protoplanetary (PPNe)
* Supernova remnants (SNRs)

* Category
* Commons
* Wiktionary

* 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

Stars portal

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Dark nebula. Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Astronomy:Dark_nebula&oldid=3356395"
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template