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) |
NASA Moon Missions Could Lead to Mars Travel
Fri, 27 Jun 2008 08:25:00 -0400
The next lunar rocket, Ares V, will be 38 stories tall and ready for passengers in 2020. Scheduled for completion in 2020, the lunar program may be a first step in getting to Mars.
Mars May Have Been Struck by Massive Object
Wed, 25 Jun 2008 17:47:00 -0400
There are competing reasons for why Mars' northern hemisphere is much lower in altitude than the southern hemisphere. Three papers in the journal Nature present new evidence that a massive object struck Mars, giving one of the theories a major boost.
NASA Helps Astronauts Cast Ballots from Space
Mon, 23 Jun 2008 12:53:00 -0400
Astronauts aboard the International Space Station are far away from the action in the presidential race. Luckily for them, NASA and Texas understand the unique needs of space-traveling citizens, who want their votes counted.
NASA Lander Touches Ice on Mars
Fri, 20 Jun 2008 18:55:00 -0400
For the first time, a NASA lander has touched Martian ice. Scientists say they are convinced white chunks dug up by the Phoenix craft are in fact frozen water on the Red Planet.
'Clumpy' Dirt Muddies Mars Research
Sat, 14 Jun 2008 17:46:00 -0400
A mini-drama unfolded millions of miles away this week near the North Pole of Mars when NASA's robotic lander Phoenix had trouble with a shovel-full of dirt. NPR's science correspondent David Kestenbaum wonders if there is life among the dirt on Mars.
Shuttle Discovery Crew Back on Earth
Sat, 14 Jun 2008 12:45:00 -0400
Seven astronauts have wrapped up a mission to the international space station to deliver a Japanese science module. The Kibo lab is now the biggest room on the space station.
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: [ * ]
| above the earth. Now accelerating, faster and faster, up to the interstellar medium. An invisible halo, surrounding ... | |
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