Gourt > Science > Astronomy > Interstellar Medium (3)
In astronomy, the interstellar medium (or ISM) is the matter (interstellar matter, also abbreviated by ISM) and energy (interstellar radiation field, ISRF) content that exists between the stars within a galaxy. The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae, stellar winds, and supernovae. In turn, this interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, and therefore its lifespan of active star formation.
The ISM consists of an extremely dilute (by terrestrial standards) plasma, gas and dust, consisting of a mixture of ions, atoms, molecules, larger dust grains, electromagnetic radiation, cosmic rays, and magnetic fields. The matter consists of about 99% gas and 1% dust by mass. It fills interstellar space. This mixture is usually extremely tenuous, with typical gas densities ranging from a few hundred to a few hundred million particles per cubic meter. As a result of primordial nucleosynthesis, the gas is roughly 90% hydrogen and 10% helium by number, with additional elements ("metals" in astronomical parlance) present in trace amounts.
| Component | Fractional Volume | Temperature (K) | Density (atoms/cm³) | State |
|---|---|---|---|---|
| Molecular clouds | < 1 % | 20 - 50 | 103 - 106 | hydrogen molecules |
| Cold Neutral Medium (CNM) | 1-5% | 50 - 100 | 1 - 103 | neutral hydrogen atoms |
| Warm Neutral Medium (WNM) | 10-20% | 1000 - 5000 | 10-1 - 10 | neutral hydrogen atoms |
| Warm Ionized Medium (WIM) | 20-50% | 103 - 104 | 0.01 | ionized hydrogen |
| H II regions | ~10% | 104 | 102 - 104 | ionized hydrogen |
| Coronal gas Hot Ionized Medium (HIM) | 30-70% | 106 - 107 | 10-4 - 10-2 | highly ionized (both hydrogen and trace metals) |
Umm, missing oxygen... Oxygen Depletion in the Interstellar Medium http://arxiv.org/abs/0912.3298 #arxiv
oneeyeopen (O. Morata) Mon, 21 Dec 2009 11:14:59 -0000
Umm, missing oxygen... Oxygen Depletion in the Interstellar Medium http://arxiv.org/abs/0912.3298 #arxiv
I think i am breaking the internet with these calculations. 1 metric tonne of interstellar medium would be a cube the size of the earth.
mibi (mibi) Mon, 21 Dec 2009 06:46:00 -0000
I think i am breaking the internet with these calculations. 1 metric tonne of interstellar medium would be a cube the size of the earth.
hmm so it goes like "termination shock" > "heliosheath" > "heliopause" > "interstellar medium"
kyourinsama (Rain) Thu, 17 Dec 2009 04:00:52 -0000
hmm so it goes like "termination shock" > "heliosheath" > "heliopause" > "interstellar medium"
The Web Nebulae - An overview of nebulae, with color images and links.
Colorado Model of the Local Interstellar Cloud - The hydrogen cloud in which the Solar System is immersed. 3D pictures of the cloud, view from any direction, movie, calculate hydrogen column density in any direction.
Interstellar Medium Learning pages - About ISM from history of observation to current status of understanding.
Interstellar Molecules evolutionary cycle - Evolutionary cycle of Interstellar Organic Molecules - Fullerenes, PAHs, Polyyenes, and biomolecules.
Meta Description: [ Shantanu Rastogi's interests in Interstellar Organic Molecules ]
Nebulae - Part of a larger site on plasma physics.
Observations of Interstellar Molecules - About observation of Interstellar molecules in the ISM and Physical information obtained from them.
Meta Description: [ Observations and identification of interstellar molecules. Overview of the interstellar medium.
Rotational spectroscopy. ]
The UCL Centre for Cosmic Chemistry and Physics - University College London. Research into the chemistry which occurs throughout the universe in interstellar space.
Meta Description: [ * ]
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