UC Berkeley

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition; they provide stringent tests of general relativity; they make possible the study of faint and rare objects such as black holes and neutron stars; they are the progenitors of gravitational wave events. The components of binaries often interact, dramatically changing their evolution and giving rise to a bewildering zoo of astrophysical phenomenology. Binaries are not rare: about half of all Sun-like stars are binaries, and the binary fraction is even higher for massive stars. To understand stars -- especially massive stars -- it is thus critical to understand binaries. In the last decade, industrial-scale stellar surveys have provided exquisite spectroscopic, photometric, and astrometric data for hundreds of millions of stars in the Milky Way. The goal of this thesis has been to leverage this deluge of data toward new insight into the formation, evolution, and cosmic importance of binaries. On the one hand, binary population demographics represent the end state of the star formation process and thus inform theoretical star formation models. On the other, binary population demographics are an important input for stellar population models: stars in interacting binaries follow qualitatively different evolutionary histories from single stars of similar mass and composition. An improved census of the binary population thus has broad utility across astrophysics. Among other results, this thesis expands the total number of binaries known by more than a factor of 10. The methods developed here are expected to continue to bear fruit in the coming decades as panchromatic surveys look ever deeper into the Galaxy.