Chandrasekhar and modern stellar dynamics

• Published in: Fluid Flows To Black Holes pp. 137 - 149
• Main Author: Evans, N. W.
• Format: Book Chapter
• Language: English
• Published: WORLD SCIENTIFIC 01.12.2011
• Subjects: general – Galaxy; kinematics and dynamics – galaxies; celestial mechanics – stellar dynamics – galaxies; stellar populations
• ISBN: 9789814374767; 9789814405270; 9789814374774; 9814374768; 9814374776; 9814405272
• DOI: 10.1142/9789814374774_0010

Stellar dynamics occupied Chandrasekhar’s interest for a brief interlude between his more prolonged studies of stellar structure and radiative transfer. This paper traces the history of one of his ideas – namely, that the shape of the galactic potential controls the orientation of the stellar velocity dispersion tensor. It has its roots in papers by Eddington (1915) and Chandrasekhar (1939), and provoked a fascinating dispute between these two great scientists – less well-known than their famous controversy over the white dwarf stars. In modern language, Eddington claimed that the integral curves of the eigenvectors of the velocity dispersion tensor provide a one-dimensional foliation into mutually orthogonal surfaces. Chandrasekhar challenged this, and explicitly constructed a counter-example. In fact, the work of neither of these great scientists was without flaws, though further developments in stellar dynamics were to ultimately draw more on Eddington’s insight than Chandrasekhar’s. We conclude with a description of modern attempts to measure the orientation of the velocity dispersion tensor for populations in the Milky Way Galaxy, a subject that is coming into its own with the dawning of the age of precision astrometry.