Theory of Spiral Structure

Abstract

It is an honor for me to continue the discussion of galactic spirals following Professor Bok, who has contributed to the subject for many years. My experience has been relatively short. My first encounter with the study of galactic spirals occurred in 1961, when I was invited by Professor Bengt Strömgren to attend a conference on interstellar matter at Princeton, N.J. There I first learned about the winding dilemma from Professor Jan Oort. After the conference, Professor Lodewijk Woltjer, who edited the Proceedings, visited me for about a month. Thus, I began slowly to learn about spiral galaxies and to work on the subject. It turned out to be an extremely rewarding experience, for the observational data were already ripe for theoretical analysis, and the hydromagnetic theory of spiral arms was clearly encountering great difficulties. Since I was not educated as an astronomer, I owe my gratitude to Professors Strömgren, Woltjer, and Kevin Prendergast, on whom I depended for correct astronomical facts as I started my work. Without their help, I would not be standing here today. Later on, I was to receive help from many other distinguished astronomers, including Professor Bok from whom you just heard. I am greatly impressed with the community of astronomers as a dedicated group of scientists.