Molecular Cloud

7/25/2019 Molecular Cloud

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Molecular cloud

From Wikipedia, the free encyclopedia

See also: Solar nebula

Within a few million years the light from bright stars will have boiled away this molecularcloud of gas and dust. The cloud has broken off from the Carina ebula. ewly formed stars

are visible nearby, their images reddened by blue light being preferentially scattered by the

pervasive dust. This image spans about two light!years and was taken by the "ubble Space

Telescopein #$$$.

% molecular cloud, sometimes called a stellar nursery&if star formationis occurring

within', is a type ofinterstellar cloud, the density and si(e of which permit the formation of

molecules, most commonly molecular hydrogen&")'. This is in contrast to other areas of the

interstellar medium that contain predominantly ioni(ed gas.

*olecular hydrogen is difficult to detect by infrared and radio observations, so the molecule

most often used to determine the presence of ")is carbon mono+ide&C'. The ratio between

Cluminosityand ")massis thought to be constant, although there are reasons to doubt this

assumption in observations of some othergala+ies.-#

Contents

# ccurrence

) Types of molecular cloud

o ).# /iant molecular clouds

o ).) Small molecular clouds

o ).0 "igh!latitude diffuse molecular clouds

0 1rocesses

o 0.# Star formation

o 0.) 1hysics
https://en.wikipedia.org/wiki/Solar_nebulahttps://en.wikipedia.org/wiki/Carina_Nebulahttps://en.wikipedia.org/wiki/Hubble_Space_Telescopehttps://en.wikipedia.org/wiki/Hubble_Space_Telescopehttps://en.wikipedia.org/wiki/Star_formationhttps://en.wikipedia.org/wiki/Interstellar_cloudhttps://en.wikipedia.org/wiki/Interstellar_cloudhttps://en.wikipedia.org/wiki/Molecular_hydrogenhttps://en.wikipedia.org/wiki/Ionized_gashttps://en.wikipedia.org/wiki/Carbon_monoxidehttps://en.wikipedia.org/wiki/Luminosityhttps://en.wikipedia.org/wiki/Luminosityhttps://en.wikipedia.org/wiki/Masshttps://en.wikipedia.org/wiki/Masshttps://en.wikipedia.org/wiki/Galaxyhttps://en.wikipedia.org/wiki/Galaxyhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-1https://en.wikipedia.org/wiki/Molecular_cloud#Occurrencehttps://en.wikipedia.org/wiki/Molecular_cloud#Types_of_molecular_cloudhttps://en.wikipedia.org/wiki/Molecular_cloud#Giant_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#Small_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#High-latitude_diffuse_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#Processeshttps://en.wikipedia.org/wiki/Molecular_cloud#Star_formationhttps://en.wikipedia.org/wiki/Molecular_cloud#Physicshttps://en.wikipedia.org/wiki/Carina_Nebulahttps://en.wikipedia.org/wiki/Hubble_Space_Telescopehttps://en.wikipedia.org/wiki/Hubble_Space_Telescopehttps://en.wikipedia.org/wiki/Star_formationhttps://en.wikipedia.org/wiki/Interstellar_cloudhttps://en.wikipedia.org/wiki/Molecular_hydrogenhttps://en.wikipedia.org/wiki/Ionized_gashttps://en.wikipedia.org/wiki/Carbon_monoxidehttps://en.wikipedia.org/wiki/Luminosityhttps://en.wikipedia.org/wiki/Masshttps://en.wikipedia.org/wiki/Galaxyhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-1https://en.wikipedia.org/wiki/Molecular_cloud#Occurrencehttps://en.wikipedia.org/wiki/Molecular_cloud#Types_of_molecular_cloudhttps://en.wikipedia.org/wiki/Molecular_cloud#Giant_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#Small_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#High-latitude_diffuse_molecular_cloudshttps://en.wikipedia.org/wiki/Molecular_cloud#Processeshttps://en.wikipedia.org/wiki/Molecular_cloud#Star_formationhttps://en.wikipedia.org/wiki/Molecular_cloud#Physicshttps://en.wikipedia.org/wiki/Solar_nebula


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2 See also

3 4eferences

5 6+ternal links

Occurrence

*olecular cloud 7arnard 58, about 399 ly distant and 9.3 ly in diameter.

Within the *ilky Way,molecular gas clouds account for less than one percent of the volume

of theinterstellar medium&S*', yet it is also the densest part of the medium, comprising

roughly half of the total gas mass interior to the Sun;s galactic orbit. The bulk of the molecular

gas is contained in a ring between 0.3 and the

time it takes for material to pass through the arm region. -2

Circinus molecular cloud has a mass around )39,999 times that of the Sun.-3

?ertically to the plane of the gala+y, the molecular gas inhabits the narrow midplane of the

galactic disc with a characteristic scale height, Z, of appro+imately 39 to


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This distribution of molecular gas is averaged out over large distances@ however, the small

scale distribution of the gas is highly irregular with most of it concentrated in discrete clouds

and cloud comple+es.-)

Types of molecular cloud

Giant molecular clouds

1art of the Taurus *olecular Cloud.-


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Bistribution of molecular gas in 09 merging gala+ies.-#)

Small molecular clouds

*ain article:7ok globule

solated gravitationally!bound small molecular clouds with masses less than a few hundred

times that of the Sun are called7ok globules. The densest parts of small molecular clouds are

euivalent to the molecular cores found in /*Cs and are often included in the same studies.

High-latitude diffuse molecular clouds

*ain article:nfrared cirrus

n #$82 4%Sidentified a new type of diffuse molecular cloud.-#0These were diffuse

filamentary clouds that are visible at high galactic latitudes. These clouds have a typical

density of 09 particles per cubic centimeter.-#2

Processes

Doung stars in and around molecular cloud Cepheus7. 4adiation from one bright, massive

star is destroying the cloud &from top to bottom in this image' while simultaneously triggering

the formation of new stars.-#3

Star formation
https://en.wikipedia.org/wiki/Molecular_cloud#cite_note-12https://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Infrared_cirrushttps://en.wikipedia.org/wiki/Infrared_cirrushttps://en.wikipedia.org/wiki/IRAShttps://en.wikipedia.org/wiki/IRAShttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-13https://en.wikipedia.org/wiki/Galactic_coordinate_systemhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-14https://en.wikipedia.org/wiki/Molecular_cloud#cite_note-14https://en.wikipedia.org/wiki/Cepheus_(constellation)https://en.wikipedia.org/wiki/Cepheus_(constellation)https://en.wikipedia.org/w/index.php?title=Triggered_star_formation&action=edit&redlink=1https://en.wikipedia.org/wiki/Molecular_cloud#cite_note-15https://en.wikipedia.org/wiki/Molecular_cloud#cite_note-12https://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Bok_globulehttps://en.wikipedia.org/wiki/Infrared_cirrushttps://en.wikipedia.org/wiki/IRAShttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-13https://en.wikipedia.org/wiki/Galactic_coordinate_systemhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-14https://en.wikipedia.org/wiki/Cepheus_(constellation)https://en.wikipedia.org/w/index.php?title=Triggered_star_formation&action=edit&redlink=1https://en.wikipedia.org/wiki/Molecular_cloud#cite_note-15


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*ain article:Star formation

The formation of starsoccurs e+clusively within molecular clouds. This is a natural

conseuence of their low temperatures and high densities, because the gravitational force

acting to collapse the cloud must e+ceed the internal pressures that are acting AoutwardA to

prevent a collapse. There is observed evidence that the large, star!forming clouds are confinedto a large degree by their own gravity &like stars, planets, and gala+ies' rather than by e+ternal

pressure. The evidence comes from the fact that the AturbulentA velocities inferred from C

linewidth scale in the same manner as the orbital velocity &a virialrelation'.

Physics

*olecular cloud 4%S #535)!0$3$, clearly visible as an orange smudge among the many

stars at the center of the image.-#5

The physics of molecular clouds are poorly understood and much debated. Their internal

motions are governed by turbulencein a cold, magneti(edgas, for which the turbulent

motions are highly supersonicbut comparable to the speeds of magnetic disturbances. This

state is thought to lose energy rapidly, reuiring either an overall collapse or a steady

reinEection of energy. %t the same time, the clouds are known to be disrupted by some process

>most likely the effects of massive stars>before a significant fraction of their mass has

become stars.

*olecular clouds, and especially /*Cs, are often the home of astronomical masers.
https://en.wikipedia.org/wiki/Star_formationhttps://en.wikipedia.org/wiki/Star_formationhttps://en.wikipedia.org/wiki/Starhttps://en.wikipedia.org/wiki/Virial_theoremhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-16https://en.wikipedia.org/wiki/Turbulencehttps://en.wikipedia.org/wiki/Magnetismhttps://en.wikipedia.org/wiki/Supersonichttps://en.wikipedia.org/wiki/Supersonichttps://en.wikipedia.org/wiki/Astrophysical_maserhttps://en.wikipedia.org/wiki/Star_formationhttps://en.wikipedia.org/wiki/Starhttps://en.wikipedia.org/wiki/Virial_theoremhttps://en.wikipedia.org/wiki/Molecular_cloud#cite_note-16https://en.wikipedia.org/wiki/Turbulencehttps://en.wikipedia.org/wiki/Magnetismhttps://en.wikipedia.org/wiki/Supersonichttps://en.wikipedia.org/wiki/Astrophysical_maser

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Molecular Cloud