Author ORCID Identifier

https://orcid.org/0000-0002-8340-614X

Semester

Spring

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Sean McWilliams

Committee Member

Zachariah Etienne

Committee Member

Aldo Romero

Committee Member

Tudor Stanescu

Abstract

The modeling of black hole binaries requires accurate descriptions of both their relativistic vacuum dynamics and their interaction with surrounding astrophysical environments. Although these problems are often treated separately, this dissertation develops a unified view: key observables of black hole binary systems can be understood by identifying the dynamical instabilities that control their evolution. In the vacuum problem, the relevant unstable structure is associated with the remnant spacetime and its role in shaping the merger-ringdown gravitational waveform. In the environmental problem, the relevant instability is the epicyclic instability of orbits in the binary potential, which controls the location and evolution of the circumbinary gap. The first part of this dissertation develops the Spinning Effective-to-Backwards One Body framework, a hybrid waveform model that combines an Effective-One-Body inspiral with a Backwards-One-Body description of the merger and ringdown. This construction reduces reliance on phenomenological numerical-relativity calibration while retaining competitive waveform accuracy for aligned-spin black hole binaries. The model provides a physically motivated map from the inspiral to the remnant-dominated regime and offers a transparent path toward more interpretable waveform models for next-generation gravitational-wave astronomy. The second part investigates the interaction between black hole binaries and circumbinary accretion disks. Using Newtonian hydrodynamic simulations and analytical epicyclic-stability theory, this dissertation shows that circumbinary gaps are maintained on orbital timescales by instabilities driven by the binary potential, rather than solely by long-timescale resonant torque balance. This framework is extended to inclined disk-binary systems, where it predicts an unstable sector near intermediate inclinations and explains persistent time-dependent disk oscillations. Together, these results show that instability-based modeling provides a common analytical language for understanding gravitational-wave signals and electromagnetic environments of black hole binaries. This perspective strengthens the physical interpretability of waveform models, clarifies the dynamics of circumbinary disks, and contributes to the theoretical foundation needed for multi-messenger observations with future detectors.

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