UC Santa Cruz

Despite spanning more than ten orders of magnitude in physical scale, common-envelope interactions and galactic bars are governed by the same fundamental process: gravitational torques redistribute angular momentum, drive dissipation, and reshape self-gravitating systems far from equilibrium. In common envelopes, this transport proceeds through hydrodynamical drag and shock-driven dissipation in collisional gas, while in barred galaxies it emerges through largely collisionless stellar dynamics. This dissertation explores how these processes govern the evolution of astrophysical systems across vastly different environments.This thesis is divided into two parts. The first and primary part investigates interacting binary evolution, focusing on common-envelope (CE) inspiral, stellar mergers, luminous red novae, and Thorne–Żytkow object (TŻO) formation. Using one-dimensional stellar evolution calculations together with three-dimensional hydrodynamical simulations, I examine how orbital energy and angular momentum are redistributed during compact-object inspiral inside massive stellar envelopes. These studies revisit the long-standing paradigm for classical TŻO formation and demonstrate that angular momentum deposited during inspiral naturally produces rotationally supported accretion flows and strong feedback, challenging the assumptions of long-term quasi-spherical accretion. Instead, the simulations favor the formation of thin-envelope TŻOs, in which disk accretion onto an embedded compact remnant powers the removal of most of the stellar envelope and may generate high-energy transients such as ultra-long gamma-ray bursts. I further investigate the hydrodynamical response of mildly evolved CE donor stars relevant to luminous red novae, showing that their observational diversity depends not only on ejecta mass, but also on the temporal structure of the outflow and the transition between impulsive ejection and prolonged mass-loss evolution. The second part of this dissertation examines the secular evolution of galactic bars using observations from the Hubble Space Telescope and Galaxy Zoo. By constructing and analyzing a catalog of galactic bar measurements across cosmic time, I investigate how angular momentum redistribution shapes bar structure and drives the long-term dynamical evolution of disk galaxies.Together, these studies demonstrate how gravitational torques and dissipative processes govern the evolution of astrophysical systems across an enormous range of scales, from compact stellar mergers to galactic structure.