Theses and Dissertations at Montana State University (MSU)
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Item Numerical methods for rotating compact objects in modified gravity theories(Montana State University - Bozeman, College of Letters & Science, 2020) Sullivan, Andrew Patrick Kyung; Chairperson, Graduate Committee: Neil J. Cornish and Nicolas Yunes (co-chair); Nicolas Yunes was a co-author of the article, 'Slowly-rotating neutron stars in massive bigravity' in the journal 'Classical and quantum gravity' which is contained within this dissertation.; Nicolas Yunes, and Thomas Sotiriou were co-authors of the article, 'Numerical black hole solutions in modified gravity theories: spherical symmetry case' in the journal 'Physical review D' which is contained within this dissertation.; Nicolas Yunes, and Thomas Sotiriou were co-authors of the article, 'Numerical black hole solutions in modified gravity theories: axial symmetry case' submitted to the journal 'Physical review D' which is contained within this dissertation.Detailed observations of phenomena involving compact objects will provide us with a new avenue to test general relativity in the strong field regime. So as to not bias our analysis of these new experiments, we require knowledge of the spacetimes around these objects both within and beyond general relativity. Here I will describe work that applies two specific methods to solve the modified Einstein's equations that describe the exotic spacetimes beyond general relativity for neutron stars and black holes. The first method is a fourth-order Runge-Kutta-Fehlberg ordinary differential equation numerical integrator method. The second method is a relaxed Newton- Raphson method applied to a system of nonlinear partial differential equations. Using these methods, we solve for the spacetimes of slowly rotating neutron stars in massive bigravity and rotating black holes in scalar Gauss-Bonnet gravity in a theory independent methodology. We validate our numerical methods by applying them to compact objects in general relativity and using them to recover known perturbative solutions. We can then compare the fully nonlinear solutions to these perturbative solutions and comment on their differences. We then use these numerical solutions to calculate the physical observables of these systems and finally construct analytic fitted models that can be used in rapid computation methods that future experiments may use to constrain the free parameters in these theories.Item The structure of energy-extracting black hole magnetospheres(Montana State University - Bozeman, College of Letters & Science, 2019) Thoelecke, Kevin; Chairperson, Graduate Committee: Yves U. IdzerdaSpinning black holes can store enormous amounts of rotational energy. Efficiently extracting that rotational energy can lead to significant energy outflows capable of powering very high energy astrophysical phenomena, such as gamma-ray bursts and active galactic nuclei. Black holes are unique in that they do not exist as physical objects in the same way a rock, planet, or star exists; instead, black holes exist only as spacetime curvature. As such processes for extracting a black hole's rotational energy are largely unique to black holes. This work explores one such process, the extraction of a black hole's rotational energy via an appropriately configured magnetosphere. Both analytic perturbation techniques and numerical codes are developed in order to solve for thousands of energy-extracting black hole magnetospheres. Those magnetospheres broadly sample the relevant solution space, allowing correlations to be drawn between different rates of black hole rotational energy and angular momentum extraction and global magnetosphere structure. The most fundamental behavior discovered is that magnetospheres that extract the most energy per unit angular momentum direct that energy away from the black hole's rotational axis, while magnetospheres that extract the least amount of energy per unit angular momentum direct that energy into jet-like structures aligned with the black hole's rotational axis. Exploration of the solutions obtained also suggests that magnetospheres most compatible with nearby accreting matter can very naturally launch jets, implying that black hole energy extraction and jet launching are likely to be concurrent and common features of astrophysical black hole magnetospheres.Item Superfluid effects on thermal evolution and rotational dynamics of neutron stars(Montana State University - Bozeman, College of Letters & Science, 2001) Larson, Michelle BeauvaisItem Transpirational heat and momentum transfer from a rotating cylinder(Montana State University - Bozeman, College of Engineering, 1974) Spannuth, Robert JohnItem Rotation patterns in the large-scale solar corona(Montana State University - Bozeman, College of Letters & Science, 1999) Weber, Mark AlanItem Rotation and dynamics for simple solenoidal maps of Tori(Montana State University - Bozeman, College of Letters & Science, 2012) Mathison, Mark Tyler; Chairperson, Graduate Committee: Jaroslaw KwapiszThe rotation number for a circle map has provided a complete and useful classification for that class of maps. In higher dimensions there is still progress to be made towards obtaining a more complete understanding of the relationship between the map and its average rotation. In this dissertation, we explore a class of homeomorphisms on the d dimensional torus T d that preserve each leaf of a foliation of the torus into parallel lines densely winding on T d. First the rotation sets of such maps are explored, with particular emphasis on those maps that have a single fixed point; zero is necessarily an element of those rotation sets. Conditions are found that show when these maps have a non-trivial rotation set. When such maps, with non trivial rotation sets, are created as the time-one map of a flow it is shown that the existence of merely two, or infinitely many ergodic measures is connected to the solvability of a cohomological equation. An example, of the infinitely many ergodic measure case, is provided. Finally, we explore on T ² maps without a fixed point that happen to also have a point whose orbit has bounded deviation from the mean rotation. Such maps are seen to be akin to circle maps with irrational rotation number; the irrationally sloped foliation leads to the map being semi-conjugate to an irrational translation of T ².