Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session C16: Compact Object Structure and Magnetic Fields |
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Sponsoring Units: DAP DGRAV Chair: Zaven Arzoumanian, NASA Room: B232-233 |
Saturday, April 14, 2018 1:30PM - 1:42PM |
C16.00001: Faithful Representations of Causal Barotropic Neutron Star Equations of State Lee Lindblom Parameterized representations of the neutron-star equation of state are used in efforts to measure the properties of the high density matter in those stars using astronomical observations. New representations are presented here that are capable of representing any equation of state to any desired level of accuracy, and that impose causality and thermodynamic stability constraints automatically on those equations of state. Numerical tests are presented that measure how well these new parameterizations represent a collection of published theoretical neutron-star equations of state. [Preview Abstract] |
Saturday, April 14, 2018 1:42PM - 1:54PM |
C16.00002: The Deconfinement Phase Transition in Proto-Neutron-Star Matter Jacob Roark Neutron stars have masses between 1.4 and 3 M$_{\odot}$, all packed into a sphere just 12 to 13 km across (roughly the size of Manhattan). Consequently, neutron stars exhibit some the of highest material densities in the universe, averaging around 7$\times$10$^{17}$ kg/m$^3$, over three times the density of an atomic nucleus. Under such astronomical pressures, some very interesting, novel states of matter can be achieved, such as quark matter, in which hadrons effectively dissolve and quark deconfinement occurs. In this work, we study in detail the deconfinement phase transition that takes place in hot/dense nuclear matter in the context of neutron stars and proto-neutron stars (in which lepton fraction is fixed). The possibility of different mixtures of phases with different locally and globally conserved quantities is considered in each case. For this purpose, the Chiral Mean Field (CMF) model, an effective relativistic model that includes self-consistent chiral symmetry restoration and deconfinement to quark matter, is employed. Finally, we compare our results with data provided by PQCD for different temperatures and conditions. [Preview Abstract] |
Saturday, April 14, 2018 1:54PM - 2:06PM |
C16.00003: Consequences of Axial Symmetry on Compact Stellar Objects Omair Zubairi, Fridolin Weber Compact objects with high magnetic fields such as magnetars and/or neutron stars, which may contain color-superconducting quark matter cores can break from standard spherical symmetry and are expected to be deformed, making them oblong spheroids with distinct polar and equatorial radii. Recent studies on the stellar structure of these deformed stars indicate that the mass could either increase or decrease depending on the shape of these objects. Thus, due to these deformations, the gravitational quadrupole moment (mass distribution) of these compact stars is not homogeneous and is expected to be non-zero. In this work, we examine this inhomogeneity by computing the gravitational mass quadrupole moment of non-rotating deformed neutron stars in the framework of general relativity and investigate any changes from conventional spherical models. [Preview Abstract] |
Saturday, April 14, 2018 2:06PM - 2:18PM |
C16.00004: Delta isobars in neutron star matter William Spinella, Fridolin Weber The possible formation of hyperons and delta isobars ($\Delta$s) in neutron stars remains an open question and active area of research. While the meson-hyperon coupling constants can be somewhat constrained by experiment and theory, few results exist that can be used to unambiguously constrain the meson-$\Delta$ coupling constants. In this work we investigate the parameter space of the scalar- and vector-meson-$\Delta$ coupling constants using relativistic mean-field (RMF) models. We calculate the neutron star mass, canonical radius, critical density, and $\Delta$ fraction for the coupling space with and without the inclusion of hyperons using RMF parameterizations that take into account recent constraints from nuclear physics and neutron star observations. Our results suggest that the two-solar-mass constraint set by PSR J0348+0432 does not exclude the formation of $\Delta$s in neutron star matter, and that the presence of $\Delta$s may lead to a reduction of the calculated canonical neutron star radius. [Preview Abstract] |
Saturday, April 14, 2018 2:18PM - 2:30PM |
C16.00005: Selective Excitation of Stellar Oscillations of a Magnetar with an Externally Coupled Tangled Magnetic Field Joseph Bretz, Anthony van Eysden, Bennett Link Magnetars are neutron stars with strong magnetic fields (10$^{\mathrm{15}}$ Gauss) that form tangled configurations to stabilize. Some of them produce giant flares that exhibit quasi-periodic oscillations which have been attributed to stellar oscillations that modulate the emission. A tangled magnetic field supports normal modes that agree with observed quasi-periodic oscillations. We show that for a tangled field that extends outside of the magnetar, a local deposition of energy leads to selective mode excitation. [Preview Abstract] |
Saturday, April 14, 2018 2:30PM - 2:42PM |
C16.00006: The Structure of Magnetically Dominated Black Hole Magnetospheres Kevin Thoelecke, Masaaki Takahashi, Sachiko Tsuruta In the stationary and axisymmetric limit, ideal black hole magnetospheres can be largely described by the distributions of four field-aligned conserved quantities: field line angular velocity, energy flux, angular momentum flux, and particle flux. In this talk I will present how different distributions of those conserved quantities can modify the structure of ingoing energy-extracting black hole magnetospheres in the magnetically dominated limit. Distributions that might be of more astrophysical interest will be presented, along with a discussion of the relaxation of the force-free approximation and the explicit consideration of plasma properties. [Preview Abstract] |
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