ASTR 1102 Lecture : Lecture17
Document Summary
Average density of the universe ~ 1 particle per cubic meter. 103 nearby intergalactic space (i. e. 103 particles per cubic meter) Hydrogen is ionized by ultraviolet emission from hot stars (young o and b stars) - energetic uv photons knock off electrons. H ii means ionized hydrogen (h i is normal, neutral hydrogen) When electrons recombine with hydrogen nuclei, they give off light. Characteristic pinkish color (like solar chromosphere and hydrogen lamp) There is also dust in the interstellar medium. We see large dust clouds throughout the milky way. Dust is also spread diffusely throughout the galaxy. If we look at a dusty nebula away from stars, we see blue scattered light. Nebula on the left is 3x as far away. Astronomers use infrared telescopes to see inside dark nebulae. Infrared is also more suited to very cool protostars (wien"s law) Life as a star is a constant battle . Whole life of star is battle between these forces.
