ASTRON 100 Lecture Notes - Lecture 24: Dark Matter Halo, Gravitational Energy, Density Wave Theory
Document Summary
The galaxy is mainly disk shaped, but also has an elliptical bulge. bar of stars as within the dashed circle around the sun well as a round halo of stars and dark matter. The disk is orbiting around the galactic center3 in an organized fashion. Differential rotation can produce a spiral pattern in the disk. But differential rotation alone is also too efficient in making the spiral arms. The observed spirals rarely have more than 2 turns and must be a long lasting feature. Gas/dust/stars orbit the center of the galaxy, passing through the spiral arms. Short-lived o and b stars make arms blue and bright the vicinity of the excess of . Pop i stars rotate in the disk with an orbital speed of ~220 km/s and are (on. Pop ii stars typically orbit across the disk and are mostly in the halo. they have average) bluer. fewer heavy elements and are therefore .
