The Development of Early Pulsation Theory, or, How Cepheids Are Like Steam Engines

Volume 40 number 1 (2012)

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Matthew Stanley

New York University, Gallatin School of Individualized Study, 715 Broadway, New York, NY 10003; matt.stanley@nyu.edu

Abstract

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A. S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. Surprisingly, the pulsation theory not only depended on novel developments in stellar physics, but the theory also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.