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Interstellar Medium - Coggle Diagram
Interstellar Medium
Structures
Nebulae
Emission nebulae
Reflection nebulae
Molecular clouds
Dust blocks UV, protecting molecules
Neutral hydrogen
Most of it in the disk of Milky Way
Dust clouds
Physical properties
Composition
Dust 1%
Solid core
silicate
carbon
Icy mantle
water
ammonia
methane
Gas 99%
Density
Average
1 atom / cm^3 (gas)
100 - 1000 grains per km^3 (gas)
In a nebula
100 atoms / cm^3 (gas)
Total mass
10 billion suns worth of gas in Milky Way
About 15% of visible mass in Milky Way
Interaction with light
Gas
Emission
Hot H II Regions
Glow red
Cold Neutral hydrogen
21-cm radiation from spin flip
Ultra-hot gases
X-ray emission
Cold Molecular clouds
IR and Radio from molecular vibration & rotation
Absorption
Low-density interstellar clouds
Absorption lines
Dust
Extinction
Blocking light
Scattering
Reflecting blue light out of the line of sight
Reddening
Shorter (bluer) wavelengths are scattered away; longer (redder) wavelengths make it through
Emission
Radiates (blackbody radiation) in IR according to its temperature