Discovering and characterizing binary black hole merger signals with new methods in gravitational wave data analysis

Abstract

We discuss improvements in gravitational wave (GW) data analysis and use these techniques to reanalyze binary black hole (BBH) merger signals, study the detected population, and discover undetected events in the first half of the third observing run (O3a) of the LIGO and Virgo detectors. Chapter 1 introduces GW detection. Chapter 2 presents the data analysis framework and highlights challenges limiting accuracy and precision. In chapter 3, we use a more accurate signal model to reanalyze the second BBH merger detection, GW151226, where we find an alternative solution that is preferred by the data and displays signs of precession and higher harmonics. In chapter 4, we explore the role of mass and spin priors in parameter inference of GW190521, the first source inferred by the LIGO--Virgo Collaboration (LVC) to have masses in the pair instability mass gap predicted by supernova theory. We develop a likelihood mapping method to show that the gap-avoiding solution requires the primary spin to be precessing and oriented opposite to the orbit. In chapter 5, we model the BBH population using the catalog of detections through O3a. Our results for the inferred black hole (BH) mass distribution are largely consistent with the LVC population study, but we interpret the measured spins differently. With a more flexible model of the effective spin distribution, we argue that the catalog is consistent with noisy measurements from a non-spinning population and a subpopulation of systems with positive effective spin. In chapter 6, we reanalyze the coincident O3a data in the LIGO-Hanford and LIGO-Livingston detectors using an independent pipeline, with recent methodological improvements described in the appendices. We find 10 previously undetected mergers including a number of interesting astrophysical scenarios, such as constituents in the lower and upper BH mass gaps and rapidly spinning BHs. Notably, we make the first measurement of anti-alignment between the BH spin and orbital angular momentum under the spin prior describing formation channels likely to produce such systems. These new events will impact the inferred BH mass and spin distributions, and help constrain cosmological measurements with some of the most distant sources yet detected.