Abstract

Mergers and other close interactions between astrophysical objects such as black holes and stars are powerful and energetic occurrences, capable of creating heavy elements, forming intriguing remnants, and shaping the populations of stars and compact objects around them. In this thesis, we describe two studies which examine two types of close gravitational events: isolated binary black hole mergers and dynamic stellar interactions in a dense environment. For our first study, we investigate how modifying the speed of convection in the engine behind core-collapse supernova explosions affects the population of merging binary black holes. To get an accurate picture of this population, we simulate a "universe" of isolated binary black hole mergers for each realization of our convection parameter. We use the COSMIC population synthesis code, ran for 32 metallicity bins, integrated over cosmic time and run through a gravitational wave detection model similar to LIGO-Virgo-KAGRA's third observing run. We represent our results through detection-weighted cumulative distribution functions (CDFs) of the primary black hole mass, which we plot alongside the observed distribution. We find that slower convection in the supernova engine corresponds to more low-mass binary black hole (BBH) mergers, and due to our lack of hierarchical BBH mergers (needed to represent the higher-mass end of the distribution), our CDFs rise much more quickly than their observed counterpart. We also quantitatively compare our models using Bayesian inference, finding that slower convection is preferred by the merger detection rate, whilst the shape of a quicker convection model better fits the shape of the observed distribution. For the second study, we build a methodology to closely study star-star and star-black hole interactions in the disks of active galactic nuclei (AGN), which should host many stellar and compact objects. We modify the output of the McFACTS AGN channel population synthesis code to serve as input for orbit integrations, which will reveal details of closer encounters between stars and black holes. Additionally, we use the pAGN disk modeling package to obtain inputs for the ambient gas environment. Once this methodology is completed, we will be able to quickly test many star-star and star-black hole systems flagged by McFACTS to see what types of gravitational interactions these systems undergo. For systems that get very close to one another, we will also be able to use the location information as initial conditions for a future hydrodynamic study, which may reveal whether any of these interactions could outshine their host AGN.

Publication Date

8-2026

Document Type

Thesis

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (MS)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Richard O’Shaughnessy

Advisor/Committee Member

Jason Nordhaus

Advisor/Committee Member

Andrew Robinson

Campus

RIT – Main Campus

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