Pinpointing the Origin of Noisy Compact Binary Mergers

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Gravitational waves are ripples in the fabric of spacetime, which carry information away from the source that created them, at the speed of light. Any non-spherically symmetric accelerated masses will produce gravitational waves, just at differing strengths. Compact object mergers, such as the collisions of neutron stars and black holes, are some of the strongest sources of detectable gravitational waves. Around 1.3 billion years ago, two black holes roughly 30 and 35 times the mass of the Sun collided with one another, and sent gravitational waves rippling throughout our Universe. In 2015, these gravitational waves swept through the Earth, and were detected by the LIGO interferometers. Since this groundbreaking initial discovery, nine more signals from the merger of black holes have been observed with the LIGO and the Virgo detectors. We estimate the masses of the black holes which collided to create these ten signals to be between 5 and 67 times the mass of the Sun. The black hole mass distribution is not thought to be continuous however. Simulations of metal-poor massive stars, around 130-250 the mass of the Sun, predict they end their lives in a pair instability supernova. In these stars, electron and positron pairs are created in the core, which cause the star to become unstable and collapse. In these supernovae no remnant is created. This means there should be a gap in the black hole mass distribution; there should be no black holes with masses between 50 - 130 times the mass of the Sun. Gravitational waves provide a unique way of probing this gap. The aims of this proposal are twofold. Our first aim is to map out the gap in the black hole mass distribution using gravitational-wave observations. The techniques we need to develop to be capable of probing this mass gap will also lead us toward our second goal - facilitating future joint gravitational-wave and electromagnetic observations.The first and only gravitational-wave signal from a neutron star coalescence, was almost simultaneously detected with gamma rays. In subsequent hours and days, the counterpart was observed across the electromagnetic spectrum. With these spectacular observations, we have been able to determine the nature of short gamma ray bursts and understand where much of the heavy elements are made. This proposal will maximise the chances of making further multi-messenger observations, which will be vital for probing many areas of physics, including estimating the expansion of the Universe.Although these two goals are very distinct, the techniques we need to develop to achieve these objectives are very similar. Both aims rely on investigating and improving the output of gravitational-wave detectors. This proposal will therefore develop novel methods of overcoming and understanding the variation of gravitational-wave detector noise. In addition to achieving the goals of this proposal, this research will have far reaching consequences in other areas of gravitational-wave astronomy. For example, our work will allow for more rigorous tests of General Relativity to be performed and ensure confident detections of gravitational-wave signals that are different to those that have currently been observed.