Date of Graduation

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Space & Planetary Sciences

Advisor/Mentor

Kennefick, Daniel J.

Committee Member

Kennefick, Julia D.

Second Committee Member

Lehmer, Bret D.

Third Committee Member

Oliver, William F. III

Fourth Committee Member

Van Horn-Morris, Jeremy

Keywords

emri; emris; gravitational-waves; gravity; lisa; peeps

Abstract

Scattering events around a massive black hole will occasionally toss a stellar-mass compact object into an orbit around the massive black hole, beginning an extreme mass ratio inspiral. The early stages of such a highly eccentric orbit will not produce detectable gravitational waves as the source will only be in a suitable frequency band briefly when it is close to periapsis during each long-period orbit. This burst of emission, firmly in the millihertz band, is the gravitational wave peep. While a single peep is not likely to be detectable, if we consider an ensemble of such subthreshold sources, spread across the universe, together they produce an unresolvable background noise that may obscure sources otherwise detectable by the Laser Interferometer Space Antenna, the proposed space-based gravitational wave detector. Previous studies of the extreme mass ratio signal confusion background focused more on parabolic orbits going very near the massive black hole and on events near the galactic center. We seek to improve this characterization by implementing numerical kludge waveforms that can calculate highly eccentric orbits with relativistic effects focusing on orbits that are farther away from the massive black hole and thus less likely to be detectable on their own but will otherwise contribute to the background signal confusion noise. Here we present the waveforms and spectra of the gravitational wave peeps generated from recent calculations of extreme mass ratio inspirals/bursts capture parameters and discuss how these can be used to estimate the signal confusion noise generated by such events. We demonstrate the effects of changing the orbital parameters on the resulting spectra as well as showing direct comparisons to parabolic orbits and why the gravitational wave "peep" needs to be studied further. We expand on this by using Illustris, a cosmological simulation to generate a massive black hole mass function to obtain the counts of massive black holes as a function of redshift and mass out to a redshift of z=3. With these counts, an expected capture rate of extreme mass ratio inspirals, and recent estimates of capture parameters, we can model a full background of peeps. With the 1470 peeps created in this study, we show that the background generated by gravitational wave peeps should not cover up otherwise detectable sources by LISA.

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