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Title Topics in solid-state astrophysics: magnetized neutron star crusts and multicomponent crusts/white dwarfs
Publication Date
Degree PhD
Discipline/Department Physics
Degree Level doctoral
University/Publisher Penn State University
Abstract Two research endeavors are described in this dissertation; both undertake problems in solid-state astrophysics, which is a branch of solid-state physics concerning the extreme conditions found within white dwarfs and the solid crusts of neutron stars. As much of our knowledge about these compact objects comes from observation of astrophysical phenomena, Chapter 1 is devoted to the phenomena, and how they can be exploited as material property probes. Several of the most interesting phenomena involve the enormous magnetic fields (B>10^12 gauss) harbored by many neutron stars, and the interaction between these fields and the charged particles within the solid crust. Accordingly, Chapter 2 reviews some theory of strongly-magnetized electrons, which both sets the stage for Chapter 3, and (hopefully) serves as a useful reference for future research. Let it now be made clear that this dissertation focuses exclusively on the ``outer crusts,'' of neutron stars, where no free neutrons are present (rho<4x10^11 g/cc), and the similarly-composed interiors of white dwarfs, which have central densities ~10^7 g/cc. For the most part we specialize to even lower densities. In Chapter 3, static and dynamic properties of low density (rho<10^6 g/cc) outer envelopes of neutron stars are calculated within the nonlinear magnetic Thomas-Fermi model, assuming degenerate electrons. A novel domain decomposition enables proper description of lattice symmetry and may be seen as a prototype for the general class of problems involving nonlinear charge screening of periodic, quasi-low-dimensionality structures, e.g. liquid crystals. We describe a scalable implementation of the method using Hypre. Over the density range considered, the effective shear modulus appears to be a factor of approximately 20 larger than in the linearly-screened Coulomb crystal model, which could have implications for observables related to astroseismology as well as low temperature phonon-mediated thermal conductivity. Other findings include incipient c'<0 elastic instabilities for both bcc and fcc lattices, reminiscent of the situation in some light actinides, and suggestive of a symmetry-lowering transition to a tetragonal or orthorhombic lattice. Chapter 4 describes a systematic search for multicomponent crystal structures, carried out for five different ternary systems of nuclei in a polarizable background of electrons, representative of accreted neutron star crusts and some white dwarfs. Candidate structures are ``bred'' by a genetic algorithm, and optimized at constant pressure under the assumption of linear response (Thomas-Fermi) charge screening. Subsequent phase equilibria calculations reveal eight distinct crystal structures in the T=0 bulk phase diagrams, five of which are complicated multinary structures not before predicted in the context of compact object astrophysics. Frequent instances of geometrically similar but compositionally distinct phases give insight into structural preferences of systems with pairwise Yukawa interactions, including and extending to…
Subjects/Keywords neutron stars; white dwarfs; dense matter; magnetic fields; numerical methods
Rights Unrestricted
Country of Publication us
Record ID oai:etda.libraries.psu.edu/oai/27294
Repository psu
Date Retrieved
Date Indexed 2017-01-24
Grantor Penn State University

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…xiv 83 Acknowledgments I thank my advisor, Vin Crespi, for his continuous support and generosity, as well as his wide-ranging interests in condensed matter physics, which led me to the fascinating subject of neutron star crusts. Ben Owen also…

…shy of typical pulsar fields, and 8 orders of magnitude less than magnetar fields. Fortunately, a growing list of astrophysical phenomena can (when precision measurements are made) be used to probe compact object matter. Magnetic neutron…

…equation of state (EOS) for matter near the nuclear saturation density ' 2.7 × 1014 g/cc, a problem of intense theoretical interest. For a recent review, see Lattimer [3]. The past five years has seen precision mass measurements of…

…they rule out several theoretical models in which the neutron star core is filled with “exotic” matter such as deconfined quarks, kaon condensates, and hyperons [3,5]. These exotic models tend to have a soft EOS near the stellar center, and…

…builds up in excess of the crustal yield stress, but the precise relationship between quake and flare is an unsettled 5 matter [13]. Additional evidence for the starquake scenario is provided by quasiperiodic oscillations (QPOs) of x…