Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
3 results
Search Results
Item Exploring the low-frequency gravitational-wave universe with pulsar timing arrays(Montana State University - Bozeman, College of Letters & Science, 2022) Becsy, Bence; Chairperson, Graduate Committee: Neil J. Cornish; This is a manuscript style paper that includes co-authored chapters.Pulsar timing arrays monitor millisecond pulsars to detect gravitational waves with nanohertz frequencies. They provide valuable information about various astophysical processes inaccessible to electromagnetic observations. In particular, they could shed light on unsolved problems related to the formation and evolution of supermassive black holes. We present several new methods which will help us fully realize the detection potential of pulsar timing arrays. We explore how the large collection of supermassive black hole binaries in the Universe can appear as a stochastic gravitational wave background, and how it might also result in a few individually detectable binaries. We describe a new method to efficiently search for such individual binaries, and also how we can detect multiple binaries in the presence of the confusion noise from the stochastic background. Finally, we introduce a new approach to search for generic gravitational-wave bursts, which enables us to hunt for unexpected new types of sources on the nanohertz gravitational-wave sky.Item Testing alternative theories of gravity using low frequency gravitational waves(Montana State University - Bozeman, College of Letters & Science, 2019) O'Beirne, Logan Tyler; Chairperson, Graduate Committee: Neil J. Cornish; Bennett Link (co-chair); Logan O'Beirne, Stephen R. Taylor and Nicolas Yunes were co-authors of the article, 'Constraining alternative theories of gravity using pulsar timing arrays' in the journal 'Physical review letters' which is contained within this thesis.; Neil J. Cornish were co-authors of the article, 'Constraining the polarization content of gravitational waves with astrometry' in the journal 'Physical review D' which is contained within this thesis.; Neil J. Cornish, Sarah J. Vigeland and Stephen R. Taylor were co-authors of the article, 'Constraining alternative polarizations of continuous gravitational waves using pulsar timing arrays' submitted to the journal 'Physical review D' which is contained within this thesis.General Relativity aptly describes current gravitational observations. However, there is great theoretical interest in its validity in untested regimes. Alternative theories of gravity attempt to relax some of the assumptions made, leaving distinct signatures that are absent in Einstein's theory, namely the presence of alternative polarizations of gravitational waves that manifest from the emission of gravitational scalar and vector dipole radiation in black hole binaries. To study this lower order multipole of radiation, it is desirable to work in a regime where the quadrupolar tensor radiation of general relativity is as quiet as possible. This motivates working with supermassive black hole binaries in their slowly evolving inspiral phase, when they are well separated from merger, emitting low frequency gravitational waves. Using a frequentist framework, we study the detectability of a stochastic background of each polarization using pulsar timing arrays, which is currently the most technically developed and viable method for studying low frequency gravitational waves, correlating the observed time delays of pulsars. We also find that astrometry, which measures transverse displacements of the apparent position of stars, turns out to have a very similar correlation structure as the time delays measured by pulsar timing arrays. We lastly study how effective using a pulsar timing array is at studying a loud, foreground binary with these alternative polarizations, using a Bayesian framework. Low frequency gravitational wave astronomy proves advantageous for studying these exotic signatures.Item Measuring surface temperature of isolated neutron stars and related problems(Montana State University - Bozeman, College of Letters & Science, 2001) Teter, Marcus Alton