Ring Galaxies
	• Cartwheel is an example we’ve already seen. Appear to result from small impact parameters. • The core of the impacted galaxy can be pulled out entirely! • The rings are kinematic waves.  Companion temporarily draws stars into the center. Oscillations are set up and driven by disk gravity, and a density wave slowly propogates toward the outer part of the disk.  Density waves cause star formation! • Will examine some aspects of this in the homework.  Watch carefully!