UC Santa Cruz

In the era of transient, multimessenger astrophysics, dramatic interactions between stellar partners are an essential ingredient in the production of the fantastic light show to which we bear witness. Common envelope interactions, in which a star engulfs a companion, are commonly invoked as the presumed formation channel of numerous exotic close binaries and merger products, from binary black holes to too-bright Algol-type stars and the elusive Thorne-Zytkow object. In this dissertation, I apply a combination of semi-analytical models and high-resolution hydrodynamical simulations in different dimensionalities to understand the role of inspiral dynamics in defining post-common envelope outcomes and to further the development of a fully descriptive, predictive theoretical framework for common envelope. I first define the range of applicability for the common envelope drag formalism, which offers a potential alternative to both global simulations and the oversimplified energy formalism in widespread use to model common envelope outcomes. I then develop a semi-analytical framework as an alternative to the energy formalism that incorporates the physical timescales most relevant to common envelope inspiral to predict how a common envelope event will proceed. Shifting to a focus on specific outcomes, I present a numerical framework that combines one- and three-dimensional hydrodynamics to capture the computationally restrictive range of timescales relevant to stellar mergers, constraining the origins of the B[e] supergiant R4 in the Small Magellanic Cloud as a post-common envelope merger product. Finally, I demonstrate through analytical and numerical modeling of merger via common envelope that Thorne-Zytkow objects are likely not a product of common envelope evolution in field binaries.