Theses and Dissertations at Montana State University (MSU)
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Item Eccentric gravitational waves: modeling and data analysis implications(Montana State University - Bozeman, College of Letters & Science, 2020) Moore, Blake Carroll; Chairperson, Graduate Committee: Nicolas Yunes and Neil J. Cornish (co-chair); Travis Robson, Nicholas Loutrel and Nicolas Yunes were co-authors of the article, 'A Fourier domain waveform for non-spinning binaries with arbitrary eccentricity' in the journal 'Classical and quantum gravity' which is contained within this dissertation.; Nicholas Loutrel was a co-author of the article, 'A 3PN Fourier domain waveform for non-spinning binaries with moderate eccentricity' in the journal 'Classical and quantum gravity' which is contained within this dissertation.; Nicolas Yunes was a co-author of the article, 'Data analysis implications of moderately eccentric gravitational waves' submitted to the journal 'Classical and quantum gravity' which is contained within this dissertation.; Nicolas Yunes was a co-author of the article, 'Constraining gravity with eccentric gravitational waves: projected upper bounds and model selection' submitted to the journal 'Classical and quantum gravity' which is contained within this dissertation.The ground based advanced Laser Interferometer Gravitational wave Observatory (LIGO) has now made numerous detections of compact objects, ushering in an era of gravitational wave astronomy. Soon the Laser Interferometer Space Antenna (LISA) will become operational and allow for even more detections of gravitational waves. With these detections we are able to characterize the physical properties of the sources - the nature of the orbit, the parameters of the individual compact object, and the parameters of the final merged object. Beyond these source measurements, gravitational waves have proven an important test bed for validating General Relativity, as well as testing theoretical astrophysical formation scenarios of these compact binaries. In order to reach these ends, we require accurate and efficient models for the gravitational waves as seen in the detector. While current detections by ground based detectors are consistent with compact binaries in quasi-circular orbits, there are formation scenarios which suggest that some small number of detectable events will be from compact objects in eccentric orbits, and certainly a healthy number of sources detectable by LISA will be in eccentric orbits. We have derived, validated, and explored the data analysis properties of a waveform model for compact objects in eccentric orbits. In the derivation of the waveform we have employed a truncated sum of harmonics, the stationary phase approximation, and a bivariate expansion in eccentricity and orbital velocity. To explore the data analysis implications of this model we have implemented Markov Chain Monte Carlo algorithms to produce the posterior distributions on the waveform parameters. We find that our model is highly accurate for the inspiral phase of compact objects in orbits with eccentricity as high as 0.8, and very computationally efficient - taking only 90ms to evaluate on average. System parameters are best measured when the source eccentricity is about 0.4, sometimes providing two orders of magnitude better measurement than its quasi-circular counterpart, and eccentric signals can provide more stringent constraints on alternative theories of gravity.Item Testing general relativity through the computation of radiative terms and within the neutron star strong-field regime(Montana State University - Bozeman, College of Letters & Science, 2019) Saffer, Alexander; Chairperson, Graduate Committee: Nicolas Yunes; Kent Yagi and Nicolas Yunes were co-authors of the article, 'The gravitational wave stress-energy (pseudo)-tensor in modified gravity' in the journal 'Classical and quantum gravity' which is contained within this thesis.; Nicolas Yunes was a co-author of the article, 'Angular momentum loss for a binary system in Einstein-aether theory' in the journal 'Physical review D' which is contained within this thesis.; Hector O. Silva is an author and Nicolas Yunes is a co-author of the article, 'The exterior spacetime of relativistic stars in scalar-Gauss-Bonnet gravity' submitted to the journal 'Physical review D' which is contained within this thesis.The recent detection of coalescing black holes by the Laser Interferometer Gravitational-wave Observatory has brought forth the era of gravitational wave astronomy. Physicists are only now beginning to probe the mergers of compact objects that send ripples through space and time. These distortions carry with them the information from the system where they originated. The dynamics of black hole collisions and neutron star mergers are new and exciting events which were undetectable just a few years ago. Einstein's theory of General Relativity has done an excellent job of describing gravity and the information that can be extracted from gravitational systems. However, his theory contains several anomalies such as the inability to explain the inflation of the universe, the effects of dark matter and energy, the presence of singularities, as well as a failure to reconcile with quantum mechanics. Modified theories of gravity have been proposed to answer any remaining questions about gravitation while prescribing solutions to the problems General Relativity still has. The work within this thesis describes how we may study modified theories of gravity in the strong field regime through two different means. The first, is through the calculation of the rate of gravitational radiation from binary systems. This rate varies depending on the theory of gravity being studied. Comparing the theoretical predictions of these rates from alternative theories to astronomical observation will allow us to place better constraints on modified gravity and test General Relativity like never before. The second way is through the investigation of the spacetime surrounding a neutron star. Unlike black holes which emit no light, we are able to see neutron stars (more specifically pulsars) through their light curve as they rotate. The shape of the light curve is dictated by the theory of gravitation used to describe the spacetime around the neutron star. My goal of constructing such a spacetime for neutron stars in modified gravity allows for future scientists to study the light curves to be detected and place constraints on the particular theory.Item Global analysis for space-based gravitational wave observatories(Montana State University - Bozeman, College of Letters & Science, 2018) Robson, Travis James; Chairperson, Graduate Committee: Neil J. Cornish; Nicolas Yunes (co-chair); Neil Cornish and Chang Liu were co-authors of the article, 'The construction and use of LISA sensitivity curves' submitted to the journal 'Classical and quantum gravity' which is contained within this thesis.; Neil Cornish was a co-author of the article, 'Impact of galactic foreground characterization on a global analysis for the LISA gravitational wave observatory' in the journal 'Classical and quantum gravity' which is contained within this thesis.; Neil Cornish, Nicola Tamanini and Silvia Toonen were co-authors of the article, 'Detecting hierarchical stellar systems with LISA' in the journal 'Physical Review D' which is contained within this thesis.; Travis Robson, Blake Moore, Nicholas Loutrel and Nicolas Yunes were all authors of the article, 'A fourier domain waveform for non-spinning binaries with arbitrary eccentricity' in the journal 'Classical and quantum gravity' which is contained within this thesis.; Neil Cornish was a co-author of the article, 'Detecting gravitational wave bursts with LISA in the presence of instrumental glitches' submitted to the journal 'Physical review D' which is contained within this thesis.; Dissertation contains one article of which Travis Robson is not the main author.The Laser Interferometer Space Antenna (LISA) is a space-based gravitational wave detector in development under a joint venture between ESA and NASA. LISA will be sensitive to a wealth of signals from a variety of sources--both astrophysical and instrumental. Since many of these signals will be overlapping we must carry out a global analysis where we model everything believed to be present in the data simultaneously. To analyze the data this way we must understand what types of signals we expect, develop fast signal generators, and develop data analysis algorithms to handle this problem. We must also be flexible to characterize signals that we do not expect such as instrumental glitches of unknown morphology, or exotic astrophysical sources. We employ the Markov Chain Monte Carlo algorithm to address these multiple facets of the global analysis problem through a Bayesian approach. We have developed fast models for a variety of sources, characterized what we can learn about the sources, and assessed the nature of LISA's global analysis problem.Item Spin-precessing compact binaries : gravitational wave modeling and information extraction(Montana State University - Bozeman, College of Letters & Science, 2016) Chatziioannou, Katerina; Chairperson, Graduate Committee: Nicolas YunesIn this dissertation we study the effect of spin-precession on gravitational waves emitted by quasicircular compact binary systems. In their most generic configuration, compact objects in a binary system are subject to interactions between the spin and the orbital angular momenta. These interactions give rise to precessional effects that add rich structure to the emitted gravitational waveforms. We study this spin-induced structure with an emphasis on extracting the information it encodes. In particular, we construct gravitational wave models that accurately capture spin-precessional effects. We then use them to study how much information relevant to astrophysics and nuclear physics we can extract from future observations of gravitational waves from compact binary coalescences.