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