Astronomy 1011A/B Lecture Notes - Lecture 15: Orbital Speed, Radiography

• School: Western University
• Department: Astronomy
• Course: Astronomy 1011A/B
• Professor: Prof.a

Document Summary

The milky way lives in the local group. 21-cm radio waves emitted by atomic hydrogen show where gas has cooled and settled into the disk. Radio waves from carbon monoxide (co) show the locations of molecular clouds. Long-wavelength infrared emission shows where young stars are heating dust grains. Infrared light reveals stars whose visible light is blocked by gas clouds. X-rays are emitted by hot gas above and below the milky way"s disk. The orbital speed (v) and radius (r) of an object on a circular orbit around the galaxy tell us the mass (mr) w/i that orbit. Stars in the disk orbit in circles going in the same direction with a little up-and- down motion. Orbits of halo and bulge stars have random orientations. Gas from dying stars mixes new elements into the interstellar medium, which slowly cools, making the molecular clouds where stars form. Those stars will eventually return much of their matter to interstellar space.