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Brittany Griner
Robin McCollum
INTERSTELLAR MEDIUM
INTERSTELLAR MEDIUM
• Matter among the stars
• Made up of two components: gas and dust
• Gas atoms exists at a size of 10^-10 m and at density of one atom per cubic centimeter
• Dust particles exist at a size of 10^-7 m and at density 1000 per cubic kilometer
• Interstellar matter are mainly individual atoms and particles
• Wavelengths smaller than the matter from distant stars cannot penetrate the interstellar matter resulting in the dimming stars or extinction
• Because the blue, higher wavelengths are affected, stars are subject to the reddening effect
COMPOSITION
• 90% of the gas is atomic molecular hydrogen; 9% is helium; 1% consists of heavier elements
• Abundances of carbon, oxygen, silicon, magnesium, and iron are very low
• Infrared evidence suggests that it is composed of silicates, graphite, and iron which supports the theory the interstellar dust forms out of interstellar gas
• Dust probably also contains some “dirty ice” which is a frozen mixture of ordinary water ice contaminated by ammonia, methane, and other chemical compounds
PHYSICAL PROPERTIES
• Dust particles are not spherical
• Individual dust grains are apparently elongated or rod-like
• Can tell the shape because the light emitted by stars is dimmed and partially polarized by the dust
• Is heated by low-energy cosmic rays, photoionization, x-rays, photoelectric heating, chemical heating, and grain-gas heating
• Is cooled by permitted lines and fine structure cooling