Einstein's general theory of relativity describes how the curvature of spacetime is determined by the energy and momentum of massive objects. He found that his field equations admit wave solutions which he called gravitational waves: plane waves traveling at the speed of light and carrying a perturbation of the spacetime metric as they propagate throughout the universe. The physical existence of such waves was in doubt for many years, until their indirect observation via the slow orbital decay of the binary pulsar system, PSR 1913 + 16, by Russell Hulse and Joseph Taylor. At this point, the endeavor to directly observe gravitational waves was begun.

It took many years to develop experimental techniques capable of observing the tiny magnitude of strain expected from compact binary mergers (h~10^-21), but finally on September 14th 2015 the Advanced LIGO detectors succeeded in making the first observation of gravitational waves from a pair of merging black holes with the signal known as GW150914. This was a landmark moment in physics, confirming the prediction of Einstein's theory nearly one hundred years later and opening up an entirely new window with which to observe the universe. Since that date, gravitational waves have become regular cosmic messengers carrying with them information about their extreme sources and unexpected new insights in many diverse areas of physics. Without a doubt the single most informative detection has been the joint observation of gravitational waves and electromagnetic radiation from the merging neutron stars and short gamma ray burst, known as GW170817 and GW170817A, respectively. This observation marked the beginning of multi-messenger astronomy with gravitational waves and advanced our knowledge of the universe by leaps and bounds. However, as all great discoveries do, this observation brought even more unanswered questions.

While we have seen an unprecedented rate of growth in the field of gravitational wave astronomy in just a decade of observation, we are still in the early years. There is much still to learn from gravitational waves, however to get there we must aim to make as many detections as possible, building up populations of gravitational waves to reveal bulk properties of their sources. This has been the subject of my dissertation.

GstLAL is a data analysis algorithm, known as a search pipeline, used to identify quiet gravitational wave signals within the noisy LIGO, Virgo, and KAGRA strain data. My work has focused on the development and operation of this pipeline, particularly towards detecting gravitational waves in near real time to enable multi-messenger astronomy. This dissertation will overview the methods and results of the various gravitational wave searches which I have led, culminating in O(100) new detections in just a few years. I additionally present a study towards the next generation of gravitational wave observation, showing how detection in ground-based interferometers can be used to identify stellar-mass binary black hole mergers in the low-frequency data of LISA. The methods presented here all seek to advance our detection capabilities and particularly, to improve our immediate prospects for multi-messenger astronomy. The population of new gravitational wave signals which have been identified as a result of my work will certainly have long-lasting implications for astrophysics, cosmology, and fundamental physics.