David J. Kaup and Boson Stars

ABSTRACT David Kaup's 1968 paper, “Klein–Gordon Geon”, introduced one of the first detailed studies of self‐gravitating configurations of a complex scalar field, known as boson stars. These objects, formed by a massive complex scalar field interacting with gravity, provide a compelling theoretical model for understanding various phenomena in astrophysics and cosmology, particularly in the context of dark matter. Kaup's pioneering work, which considered the Einstein–Klein–Gordon equations, remains foundational in the study of nontopological solitons and self‐gravitating systems in general.