The Poincar\'e pear and Poincar\'e-Darwin fission theory in astrophysics, 1885-1901

Abstract

In the early 1880s, Henri Poincar\'e discovered a new equilibrium figure for uniformly-rotating fluid masses -- the pear, or piriform figure -- and speculated that in certain circumstances the pear splits into two unequal parts, and provides thereby a model for the origin of binary stars. The contemporary emergence of photometric and spectroscopic studies of variable stars fueled the first models of eclipsing binaries, and provided empirical support for a realist view of equilibrium figures -- including the pear -- in the cosmic realm. The paper reviews astrophysical interpretation of the Poincar\'e pear and the Poincar\'e-Darwin fission hypothesis with respect to research on variable stars from 1885 to 1901.