molecular cloud
(dense cloud)
(interstellar gas cloud that includes molecules)
A molecular cloud (or dense cloud) is
a gas cloud of sufficient size and density
and sufficiently low temperature that
molecules form, particularly molecular hydrogen
(aka HH or H2).
They are cooler than HI regions or HII regions
because too high a temperature would dissociate the molecules.
Stars form in molecular clouds, where the low temperature
leads to the highest cloud densities.
Molecular clouds are typically detected and measured by observing the
luminosity of carbon monoxide (CO), which is presumed
present. The amount and density of H2 is
estimated using the CO to H2 factor.
The cloud's temperature and density are of interest with respect
to star formation activity/potential and can be determined
from the relative strength of various molecular spectral lines.
A cloud's diameter is typically in the 5 to 200 parsec range.
The largest are termed giant molecular clouds (GMCs), a term generally used for those
on the order of a thousand solar masses and above,
and which can be as much as ten million solar masses
A magnetized molecular cloud is such a cloud with a
(significant/detectable) magnetic field.
If incoming electromagnetic radiation ionizes some of the cloud matter
making it conductive, an external magnetic field can interact
with the cloud, affecting its behavior, perhaps helping
or hindering collapses leading to star formation. A cloud's
magnetism can be inferred from the Zeeman effect,
presumably observed through Zeeman-Doppler imaging.
Some terms used for molecular clouds, or dense portions
of them, used in various contexts:
Some example molecular clouds are Taurus Molecular Cloud 1 and Serpens Cloud,
and some complexes are the Taurus-Auriga Complex,
the Rho Ophiuchi Cloud Complex,
and the Orion Molecular Cloud Complex (which includes the Orion Nebula).
(hydrogen,star formation,cloud type,molecular hydrogen,gas)
Further reading:
https://en.wikipedia.org/wiki/Molecular_cloud
https://astronomy.swin.edu.au/cosmos/m/Molecular+Cloud
https://www.daviddarling.info/encyclopedia/M/molcloud.html
https://www.sun.org/encyclopedia/molecular-clouds-and-dark-nebulae
http://spiff.rit.edu/classes/phys230/lectures/ism_gas/ism_gas.html
http://spiff.rit.edu/classes/phys230/lectures/sf/chap6_3.html
https://ned.ipac.caltech.edu/level5/Sept10/Krumholz/Krumholz_contents.html
Prefix | Example | | |
MCLD | MCLD 126.6+24.5 | rarely used | |
|
Referenced by pages:
abundances
age-metallicity relation (AMR)
age-velocity-dispersion relation (AVR)
Atacama Pathfinder Experiment (APEX)
carbon (C)
carbon dioxide (CO2)
carbon monoxide (CO)
chemical tagging
cloud
cloud fragmentation
CO ladder
CO to H2 factor (XCO)
cold gas
COMPLETE Survey
COPSS
cosmic dust
DeGaS-MC
dendrogram
dense core
dense core mass function (DCMF)
evaporating gas globule (EGG)
filament
FIRE Simulations
galaxy cloud
gas flow
giant molecular cloud (GMC)
glycine (Gly)
HI region (HI)
HII region (HII)
HL Tau
hydrogen (H)
hydrogen deuteride (HD)
hydroxyl (OH)
infrared dark cloud (IRDC)
interstellar astrophysics
interstellar medium (ISM)
Lyman-Werner photon
Mach number
main sequence fitting
maser
Messier 100 (M100)
Messier 74 (M74)
metallicity (Z)
microwave
molecular cloud turbulence
open cluster (OC)
Orion Molecular Cloud Complex
Orion Nebula (M42)
PAH emissions
photodissociation
photodissociation region (PDR)
photoevaporation
planet formation
polycyclic aromatic hydrocarbon (PAH)
position-position-velocity space (PPV)
protostar
quenched galaxy
rare designator prefixes
Rho Ophiuchi Cloud Complex
rocky planet
Sag A*
Serpens Cloud
shock wave
spectral line
SPHEREx
SSP
star formation (SF)
star formation feedback
star formation rate (SFR)
star-forming region (SFR)
stellar age determination
stellar association
submillimeter astronomy
T association
T-Tauri star (TTS)
Taurus Molecular Cloud 1 (TMC-1)
Taurus-Auriga Complex (Tau-Aur Complex)
The H2O Southern Galactic Plane Survey (HOPS)
three dimensional model
Toomre Q parameter (Q)
tracer
velocity-metallicity relation
virial parameter
water (H2O)
Whirlpool Galaxy (M51a)
Index