Speaker: Mark Cropper (MSSL)
For some time, the predominant view of spiral structure in disk galaxies has been that they are spiral density waves, developed by Lin & Shu to produce a long-standing pattern, and to avoid the spiral pattern becoming wound up. However recent numerical simulations have found it difficult to produce long-standing wave patterns, and suggest that indeed the pattern does wind up: new spiral arms are constantly being created and sheared away. I will report on our analyses of the stellar motions within the spiral arms in our simulations, give some observational evidence, and explore the implications for radial migration in spiral galaxies. I will provide a possible explanation for this behaviour in terms of the swing amplification theory of Goldreich & Lynden Bell.