Abstract

According to the currently prevailing cosmological paradigm, mergers between galaxies are an important part of their evolution. Assuming also that most galaxies contain a supermassive black hole at their center, binary supermassive black holes (BSBH) should be common products of galactic mergers.

The subject of this dissertation is the dynamical evolution of a BSBH at the center of a galaxy. I calculate the rate of change of a binary's orbital elements due to interactions with the stars of the galaxy by means of 3-body scattering experiments. My model includes a new degree of freedom - the orientation of the BSBH's orbital plane - which is allowed to change due to interaction with the stars in a rotating nucleus. The binary's eccentricity also evolves in an orientation-dependent manner. I find that the dynamics are qualitatively different compared to non-rotating nuclei: 1) The orbital orientation of a BSBH changes towards alignment with the plane of rotation of the nucleus. 2) The orbital eccentricity of a BSBH decreases for aligned BSBHs and increases for counter-aligned ones.

I then apply my model to calculate the effects of stellar environment on the gravitational wave background spectrum produced by BSBHs. Using the results of N-body/Monte-Carlo simulations, I account for the different rate of stellar interactions in spherical, axisymmetric and triaxial galaxies. I also consider the possibility that supermassive black hole masses are systematically lower than usually assumed. The net result of the new physical mechanisms included in my model is a spectrum for the stochastic gravitational wave background that has a significantly lower amplitude than in previous treatments, which could explain the discrepancy that currently exists between the models and the upper limits set by pulsar timing array observations.

Publication Date

8-7-2017

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

School of Physics and Astronomy (COS)

Advisor

David Merritt

Advisor/Committee Member

Jeremy Schnittman

Advisor/Committee Member

Michael Kerekes

Campus

RIT – Main Campus

Share

COinS