Interstellar medium

1. Interstellar medium Brittany Griner Robin McCollum

2. 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

4. 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

6. 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