Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session J14: Numerical Modeling of Neutron StarsLive
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Sponsoring Units: DGRAV Chair: Zach Etienne, West Virginia University Room: Virginia A |
Sunday, April 19, 2020 1:30PM - 1:42PM Live |
J14.00001: Numerical waveforms for neutron star mergers with the SpEC code Francois Foucart Numerical simulations of binary neutron star and black hole-neutron star mergers play an important role in the development, calibration, and testing of waveform models used by current gravitational wave detectors. In this talk, I will discuss recent efforts to improve the accuracy and availability of waveforms generated with the SpEC code, for systems involving at least one neutron star. I will also review the development and use of improved `spectral’ equations of state in merger simulations, and compare these equations of state with standard polytropic and piecewise-polytropic models in the context of accurate waveform generation. Finally, I will discuss what we have learnt about the accuracy of existing waveform models from the most accurate of these numerical simulations. [Preview Abstract] |
Sunday, April 19, 2020 1:42PM - 1:54PM Live |
J14.00002: Search for r-modes from Crab pulsar. Binod Rajbhandari, Benjamin Owen Fluid oscillations of neutron stars can be promising sources of continuous gravitational waves. R-modes are oscillations where the restoring force is the Coriolis force. The modes are damped by viscosity but can be unstable to gravitational radiation via the Chandrasekhar-Friedman-Schutz instability. When relativistic corrections are taken into consideration the mode frequency can be 1.39 to 1.57 times the spin frequency of the star and the frequency derivative can be roughly estimated in terms of the star's measured spin-down parameter. We performed a search for r-mode gravitational waves from the Crab pulsar for the entire LIGO O1 and O2 runs. We did not find any evidence of gravitational waves but instead set upper limits. [Preview Abstract] |
Sunday, April 19, 2020 1:54PM - 2:06PM Live |
J14.00003: Detectability of Interfacial Modes of Hybrid Stars with a Solid Core Shu Yan Lau, Yagi Kent During a binary compact star coalescence, the tidal effect is encoded in the phase of the emitted gravitational wave signal. The tides contain unique information to constrain the equation of state (EOS) of cold high-density matter. While the equilibrium tidal effect can be described by the tidal deformability, the dynamical part could arise from the resonant excitations of non-radial pulsation modes which depend on the detailed features of the stellar internal structures. Out of the many pulsation modes, we focus on the interfacial mode of hybrid stars with a crystalline quark matter core and fluid nuclear matter envelope. This mode originates from the discontinuities in density and shear modulus at the interface separating the quark matter and nuclear matter phase. It is of interest due to its relatively large overlap integral with the external tidal field, which implies a significant excitation amplitude, and its resonant frequency might lie within the sensitive region of ground-based gravitational wave detectors depending on the EOS. In this talk, I will present how the interfacial mode affects the waveform of a binary hybrid star coalescence and comment on its detectability with advanced LIGO and next-generation detectors based on a Fisher analysis. [Preview Abstract] |
Sunday, April 19, 2020 2:06PM - 2:18PM |
J14.00004: Binary neutron star initial data: numerical methods and a public library Joshua Faber, Tanmayee Gupte, Grace Fiacco, Trung Ha Binary neutron star mergers have long been known as a critical target for gravitational wave detection by the LIGO mission, and the recent coincident electromagnetic and gravitational wave observations of GW170817 have served to open up the dawn of the multimessenger age. To simulate such systems, it is critical to begin from relativistically self-consistent quasi-equilibrium binary configurations. Here, we describe advancements made to the publicly available Lorene code to allow for more robust generation of neutron star binaries with either high-mass components or very unequal mass components, for systems where physically motivated neutron star equation of state formulae are modeled as piecewise polytropes. We also describe the release of a publicly available binary neutron star initial data repository, intended for use by researchers using the Einstein Toolkit and other GR evolution codes. [Preview Abstract] |
Sunday, April 19, 2020 2:18PM - 2:30PM On Demand |
J14.00005: Dynamical Tides of Spinning Neutron stars Sizheng Ma, Hang Yu, Yanbei Chen Tidal effects have important imprints on gravitational waves (GWs) emitted during the final stage of the coalescence of binaries that involve neutron stars (NSs). Dynamical tides can be significant when NS oscillations become resonant with orbital motion; understanding this process is important for accurately modeling GW emission from these binaries, and for extracting NS information from GW data. In this talk, I will present some analytic understandings on the excitation of dynamical tides in spinning NSs in coalescencing binaries, including fundamental modes (f-modes) and Rossby modes (r-modes). In particular, I will show a new approximation that can lead to analytic expressions of tidal excitations to a high accuracy, and are valid in all regimes of the binary evolution: adiabatic, transition, and post-resonance. I will also show the significance of dynamical tides to learn more information about binaries with third-generation GW detectors. [Preview Abstract] |
Sunday, April 19, 2020 2:30PM - 2:42PM |
J14.00006: Dynamically stable ergostars exist: General relativistic models and simulations. Antonios Tsokaros, Milton Ruiz, Lunan Sun, Stuart Shapiro, Koji Uryu We construct the first dynamically stable ergostars (equilibrium neutron stars that contain an ergoregion) for a compressible, causal equation of state. We demonstrate their stability by evolving both strict and perturbed equilibrium configurations in full general relativity for over a hundred dynamical timescales and observing their stationary behavior. This stability is in contrast to earlier models which prove radially unstable to collapse. Our solutions are differentially rotating hypermassive neutron stars with a corresponding spherical compaction of C$=$0.3. Such ergostars can provide new insights into the geometry of spacetimes around highly compact, rotating objects and on the equation of state at supranuclear densities. Ergostars may form as remnants of extreme binary neutron star mergers and possibly provide another mechanism for powering short gamma-ray bursts. [Preview Abstract] |
Sunday, April 19, 2020 2:42PM - 2:54PM Not Participating |
J14.00007: Gravitomagnetic tidal resonances in binary inpirals Eric Poisson, Simon Alexandre Pekar The normal modes of oscillation of neutron stars have frequencies that lie beyond the band of interferometric gravitational-wave detectors, and they therefore provide little opportunity to generate resonances that could have an impact on the orbtial dynamics of binary inspirals. An exception are g-modes, which have comparatively low frequencies, and the associated resonances were studied by Lai [MNRAS 270, 611 (1994)]. Another exception is the r-modes of a rotating star, whose frequencies are a numerical factor times the spin frequency of the star, and which can therefore lie within the LIGO/Virgo frequency band. The r-modes are driven mostly by a gravitomagnetic tidal interaction (involving the post-Newtonian vector potential), and the associated resonances were studied by Flanagan and Racine [PRD 75, 044001 (2007)]. But the r-modes are a special case of the broader class of inertial modes first identified by Lockitch and Friedman [ApJ 521, 764 (1999)], and the gravitomagnetic tidal interaction drives all these modes. In this talk I describe the inertial-mode resonances that result when a rotating neutron star is subjected to gravitomagnetic tidal field produced by an orbiting companion, as well as the consequences they might have on the orbital dynamics of binary inspirals. [Preview Abstract] |
Sunday, April 19, 2020 2:54PM - 3:06PM Not Participating |
J14.00008: Higher order equations to describe r-modes in Neutron Stars Giammarco Turriziani Colonna, Benjamin Owen The structure and composition of Neutron Stars (NS) are unknown and the most promising way to understand them is through the Gravitational Waves (GW) asteroseismology. Between all the possible Quasi Normal Modes, the r-modes are the most promising source of GW because they can be unstable at an arbitrary angular velocity. The frequencies of r-mode oscillations of rotating NS can be useful for guiding and interpreting GW and electromagnetic (EM) observations, which makes this study of relevance to both LIGO scientists, and astrophysicists. The frequencies of slowly rotating, barotropic and non magnetic Newtonian stars are well known, but subject to various corrections. The most important one is the relativistic correction, and the second most important is the rapid rotation correction. For this reason we decided to study the Lockitch-Andersson-Friedman (LAF) equations, that describe r-mode oscillations of stars in General Relativity (GR), and we aim to extend these equations to higher order in the rotation rate expansion. Solving these equations would allow us to find a more precise range of frequencies than the one found in the literature. [Preview Abstract] |
Sunday, April 19, 2020 3:06PM - 3:18PM Not Participating |
J14.00009: An averaged-Lagrangian theory of self-consistent metric oscillations in matter Deepen Garg, Ilya Dodin Existing theories of gravitational-wave (GW) coupling with matter are not directly applicable to GWs that are inhomogeneous in space and have more general polarization than those in vacuum. We propose an alternative, variational formulation of this problem, which also leads to the prediction of a nonlinear average force that a GW pulse exerts on massive particles. Using this result, we derive the wave equation for collective oscillations of the self-consistent metric with general polarization, and we reproduce the Jeans instability as a limiting case. Developing further on this equation, we present corrections to geometrical optics, which are of the same order as the GW-matter interaction term for near-vacuum waves. We have also re-calculated the linearized-gravity Ricci tensor in the presence of matter, on which there has been some disagreement in the community. Electromagnetic interactions can be added similarly, which, in the future, will lead to a generalized theory of plasma waves in the astrophysical context. [Preview Abstract] |
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