Towards the extreme

Gravitational-Wave Astronomy ◽

10.1093/oso/9780198568032.003.0012 ◽

2019 ◽

pp. 250-281

Author(s):

Nils Andersson

Keyword(s):

Neutron Star ◽

Equation Of State ◽

First Principles ◽

Observational Constraints ◽

Simple Matter ◽

Matter Model ◽

The Impact

The main aspects of neutron star physics are discussed, including the problem of determing the equation of state from first principles (using a simple matter model as example). Available observational constraints on mass and radius are considered. The effect of rotation is considered and the impact of superfluidity (manifesting itself in terms of pulsar glitches) is discussed.

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Modelling strains and stresses in continuously stratified rotating neutron stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3099 ◽

2019 ◽

Author(s):

E Giliberti ◽

G Cambiotti ◽

M Antonelli ◽

P M Pizzochero

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Neutron Stars ◽

Adiabatic Index ◽

Practical Application ◽

Polytropic Equation ◽

Vela Pulsar ◽

Superfluid Vortices ◽

The Impact ◽

Stellar Configuration

Abstract We introduce a Newtonian model for the deformations of a compressible, auto-gravitating and continuously stratified neutron star. The present framework can be applied to a number of astrophysical scenarios as it allows to account for a great variety of loading forces. In this first analysis, the model is used to study the impact of a frozen adiabatic index in the estimate of rotation-induced deformations: we assume a polytropic equation of state for the matter at equilibrium but, since chemical reactions may be slow, the perturbations with respect to the unstressed configuration are modeled by using a different adiabatic index. We quantify the impact of a departure of the adiabatic index from its equilibrium value on the stressed stellar configuration and we find that a small perturbation can cause large variations both in displacements and strains. As a first practical application, we estimate the strain developed between two large glitches in the Vela pulsar showing that, starting from an initial unstressed configuration, it is not possible to reach the breaking threshold of the crust, namely to trigger a starquake. In this sense, the hypothesis that starquakes could trigger the unpinning of superfluid vortices is challenged and, for the quake to be a possible trigger, the solid crust must never fully relax after a glitch, making the sequence of starquakes in a neutron star an history-dependent process.

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Rotation-Driven Phase Transitions in the Cores of Pulsars

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194517600357 ◽

2017 ◽

Vol 45 ◽

pp. 1760035

Author(s):

Richard D. Mellinger ◽

William Spinella ◽

Fridolin Weber ◽

Gustavo A. Contrera ◽

Milva Orsaria

Keyword(s):

Phase Transitions ◽

Neutron Star ◽

Equation Of State ◽

Neutron Stars ◽

Quark Matter ◽

Nuclear Data ◽

Particle Composition ◽

Nuclear Equation Of State ◽

The Impact ◽

Gravitational Compression

In this paper, we discuss the impact of rotation on the particle composition of rotating neutron stars (pulsars). Particular emphasis is put on the formation of quark matter during stellar spin-down, driven by continuous gravitational compression. Our study is based on modern models for the nuclear equation of state whose parameters are tightly constrained by nuclear data, neutron star masses, and the latest estimates of neutron star radii.

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Neutron Star Properties: Quantifying the Effect of the Crust–Core Matching Procedure

Universe ◽

10.3390/universe6110220 ◽

2020 ◽

Vol 6 (11) ◽

pp. 220

Author(s):

Márcio Ferreira ◽

Constança Providência

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Nuclear Matter ◽

Strong Impact ◽

The Core ◽

Meta Modeling ◽

Low Mass ◽

Matching Procedure ◽

The Impact

The impact of the equation of state (EoS) crust-core matching procedure on neutron star (NS) properties is analyzed within a meta-modeling approach. Using a Taylor expansion to parametrize the core equation of state (EoS) and the SLy4 crust EoS, we create two distinct EoS datasets employing two matching procedures. Each EoS describes cold NS matter in a β equilibrium that is thermodynamically stable and causal. It is shown that the crust-core matching procedure affects not only the crust-core transition but also the nuclear matter parameter space of the core EoS, and thus the most probable nuclear matter properties. An uncertainty of as much as 5% (8%) on the determination of low mass NS radii (tidal deformability) is attributed to the complete matching procedure, including the effect on core EoS. By restricting the analysis, imposing that the same set of core EoS is retained in both matching procedures, the uncertainty on the NS radius drops to 3.5% and below 1.5% for 1.9M⊙. Moreover, under these conditions, the crust-core matching procedure has a strong impact on the Love number k2, of almost 20% for 1.0M⊙ stars and 7% for 1.9M⊙ stars, but it shows a very small impact on the tidal deformability Λ, below 1%.

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Inferring the dense nuclear matter equation of state with neutron star tides

EPJ Web of Conferences ◽

10.1051/epjconf/202225807002 ◽

2022 ◽

Vol 258 ◽

pp. 07002

Author(s):

Pantelis Pnigouras ◽

Nils Andersson ◽

Andrea Passamonti

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Direct Detection ◽

Oscillation Mode ◽

Finite Size ◽

Dense Nuclear Matter ◽

Oscillation Modes ◽

Stellar Oscillation ◽

Star Binary ◽

The Impact

During the late stages of a neutron star binary inspiral finite-size effects come into play, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal. As demonstrated in the case of GW170817—the first direct detection of gravitational waves from a neutron star binary—this can lead to strong constraints on the neutron star equation of state. As detectors become more sensitive, effects which may have a smaller influence on the neutron star tidal deformability need to be taken into consideration. Dynamical effects, such as oscillation mode resonances triggered by the orbital motion, have been shown to contribute to the tidal deformability, especially close to the neutron star coalesence, where current detectors are most sensitive. We calculate the contribution of the various stellar oscillation modes to the tidal deformability and demonstrate the (anticipated) dominance of the fundamental mode. We show what the impact of the matter composition is on the tidal deformability, as well as the changes induced by more realistic additions to the problem, e.g. the presence of an elastic crust. Finally, based on this formulation, we develop a simple phenomenological model describing the effective tidal deformability of neutron stars and show that it provides a surprisingly accurate representation of the dynamical tide close to merger.

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Neutron Star Properties in the Thomas-Fermi Model

International Journal of Modern Physics E ◽

10.1142/s0218301397000329 ◽

1997 ◽

Vol 06 (04) ◽

pp. 669-691 ◽

Cited By ~ 12

Author(s):

K. Strobel ◽

F. Weber ◽

Ch. Schaab ◽

M. K. Weigel

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Optical Potential ◽

Nucleon Nucleon ◽

Neutron Star Matter ◽

Fermi Model ◽

Cooling Behavior ◽

Nucleon Nucleon Interaction ◽

Finite Nuclei ◽

The Impact

The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to the properties of finite nuclei, the parameters of the mass formula, and the behavior of the optical potential is used to calculate the properties of β-equilibrated neutron star matter, and to study the impact of this equation of state on the properties of (rapidly rotating) neutron stars and their cooling behavior. The results are in excellent agreement with the outcome of calculations performed for a broad collection of sophisticated nonrelativistic as well as relativistic models for the equation of state.

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The effect of ionic defect interactions on the hydration of yttrium-doped barium zirconate

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06587k ◽

2021 ◽

Author(s):

Sebastian Eisele ◽

Fabian M. Draber ◽

Steffen Grieshammer

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

First Principles ◽

Barium Zirconate ◽

First Principles Calculations ◽

Defect Interactions ◽

The Impact ◽

Ionic Defect

First principles calculations and Monte Carlo simulations reveal the impact of defect interactions on the hydration of barium-zirconate.

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A Superfluid Perspective on Neutron Star Dynamics

Universe ◽

10.3390/universe7010017 ◽

2021 ◽

Vol 7 (1) ◽

pp. 17

Author(s):

Nils Andersson

Keyword(s):

Neutron Star ◽

Degrees Of Freedom ◽

Temperature Scale ◽

Fluid System ◽

Fluid Core ◽

State Of Matter ◽

Entrainment Effect ◽

Neutron Component ◽

The Impact

As mature neutron stars are cold (on the relevant temperature scale), one has to carefully consider the state of matter in their interior. The outer kilometre or so is expected to freeze to form an elastic crust of increasingly neutron-rich nuclei, coexisting with a superfluid neutron component, while the star’s fluid core contains a mixed superfluid/superconductor. The dynamics of the star depend heavily on the parameters associated with the different phases. The presence of superfluidity brings new degrees of freedom—in essence we are dealing with a complex multi-fluid system—and additional features: bulk rotation is supported by a dense array of quantised vortices, which introduce dissipation via mutual friction, and the motion of the superfluid is affected by the so-called entrainment effect. This brief survey provides an introduction to—along with a commentary on our current understanding of—these dynamical aspects, paying particular attention to the role of entrainment, and outlines the impact of superfluidity on neutron-star seismology.

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