Unified equations of state for cold nonaccreting neutron stars with Brussels-Montreal functionals. III. Inclusion of microscopic corrections to pasta phases

ABSTRACT We investigate the impact of using high-order numerical methods to study the merger of magnetized neutron stars with finite-temperature microphysics and neutrino cooling in full general relativity. By implementing a fourth-order accurate conservative finite-difference scheme we model the inspiral together with the early post-merger and highlight the differences to traditional second-order approaches at the various stages of the simulation. We find that even for finite-temperature equations of state, convergence orders higher than second order can be achieved in the inspiral and post-merger for the gravitational-wave phase. We further demonstrate that the second-order scheme overestimates the amount of proton-rich shock-heated ejecta, which can have an impact on the modelling of the dynamical part of the kilonova emission. Finally, we show that already at low resolution the growth rate of the magnetic energy is consistently resolved by using a fourth-order scheme.

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Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽

10.3390/universe6050063 ◽

2020 ◽

Vol 6 (5) ◽

pp. 63

Author(s):

Hui Wang ◽

Zhi-Fu Gao ◽

Huan-Yu Jia ◽

Na Wang ◽

Xiang-Dong Li

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Neutron Stars ◽

General Expression ◽

Equations Of State ◽

Rotation Period ◽

Ohmic Dissipation ◽

Hartree Fock ◽

Induction Equation ◽

The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

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Model Atmospheres for Cooling Neutron Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900161212 ◽

1987 ◽

Vol 125 ◽

pp. 459-459

Author(s):

Roger W. Romani ◽

Roger D. Blandford ◽

Lars Hernquist

Keyword(s):

Neutron Stars ◽

Supernova Remnants ◽

Equations Of State ◽

Black Body ◽

X Ray ◽

Electron Heat ◽

Parallel Field ◽

Effective Temperatures ◽

Calculated Model ◽

Magnetic Case

The failure of Einstein X-ray observations to detect central neutron stars in most young supernova remnants (Helfand and Becker 1984) has provided interesting constraints on cooling theories (cf. review by Tsuruta 1985). The comparison of the measured fluxes with the predicted effective temperatures is sensitive to the nature of the emitted spectrum, commonly assumed to be blackbody. The presence of a substantial absorbing atmosphere can, however, produce significant departures. We have calculated model atmospheres for unmagnetized neutron stars with effective temperatures 105K ≦ Teff ≦ 106.5K using Los Alamos opacities and equations of state (Romani 1986). We consider a range of surface compositions, since the accretion of ∼10−19M⊙ will cover the surface to the X-ray photosphere and subsequent settling in the strong gravitational field can severely deplete the heavy species. In a low Z atmosphere (eg. He) the measured X-ray flux will substantially exceed the blackbody value–the Einstein limits on Teff are correspondingly lowered (eg. by ∼1.6 for SN1006 with a helium surface). For high Z atmospheres, the flux is close to the black body value, but prominent absorption edges are present. Recent calculations of the electron heat transport in magnetized neutron star envelopes (Hernquist 1984, 1985) have shown that, contrary to earlier estimates, magnetic fields will have a small effect on the heat flux (≳ 3 for parallel field geometries and ∼1 for tangled fields). Extension of the atmosphere computations to the magnetic case is important for comparison with X-ray observations of known pulsars.

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FINITE TEMPERATURE EQUATIONS OF STATE FOR MIXED STARS

International Journal of Modern Physics D ◽

10.1142/s0218271804005389 ◽

2004 ◽

Vol 13 (07) ◽

pp. 1249-1253

Author(s):

DÉBORA P. MENEZES ◽

C. PROVIDÊNCIA

Keyword(s):

Field Theory ◽

Neutron Stars ◽

Quark Matter ◽

Finite Temperature ◽

Equations Of State ◽

Mean Field Theory ◽

Mean Field ◽

Relativistic Mean Field Theory ◽

Relativistic Mean Field

We investigate the properties of mixed stars formed by hadronic and quark matter in β-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. The calculations were performed for T=0 and for finite temperatures and also for fixed entropies with and without neutrino trapping in order to describe neutron and proto-neutron stars. The star properties are discussed. Maximum allowed masses for proto-neutron stars are much larger when neutrino trapping is imposed.

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Unified equations of state for cold non-accreting neutron stars with Brussels-Montreal functionals. I. Role of symmetry energy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty2413 ◽

2018 ◽

Cited By ~ 23

Author(s):

J M Pearson ◽

N Chamel ◽

A Y Potekhin ◽

A F Fantina ◽

C Ducoin ◽

...

Keyword(s):

Neutron Stars ◽

Symmetry Energy ◽

Equations Of State

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Fundamental physics and the absence of sub-millisecond pulsars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833521 ◽

2018 ◽

Vol 620 ◽

pp. A69 ◽

Cited By ~ 4

Author(s):

B. Haskell ◽

J. L. Zdunik ◽

M. Fortin ◽

M. Bejger ◽

R. Wijnands ◽

...

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Neutron Stars ◽

Gravitational Wave ◽

Equations Of State ◽

Rotation Frequency ◽

Hadronic Matter ◽

Spin Distribution ◽

Test Models ◽

State Of Matter

Context. Rapidly rotating neutron stars are an ideal laboratory to test models of matter at high densities. In particular, the maximum rotation frequency of a neutron star depends on the equation of state and can be used to test models of the interior. However, observations of the spin distribution of rapidly rotating neutron stars show evidence for a lack of stars spinning at frequencies higher than f ≈ 700 Hz, well below the predictions of theoretical equations of state. This has generally been taken as evidence of an additional spin-down torque operating in these systems, and it has been suggested that gravitational wave torques may be operating and be linked to a potentially observable signal. Aims. We aim to determine whether additional spin-down torques (possibly due to gravitational wave emission) are necessary, or if the observed limit of f ≈ 700 Hz could correspond to the Keplerian (mass-shedding) break-up frequency for the observed systems, and is simply a consequence of the currently unknown state of matter at high densities. Methods. Given our ignorance with regard to the true equation of state of matter above nuclear saturation densities, we make a minimal physical assumption and only demand causality, that is, that the speed of sound in the interior of the neutron star should be lower than or equal to the speed of light c. We then connected our causally limited equation of state to a realistic microphysical crustal equation of state for densities below nuclear saturation density. This produced a limiting model that gave the lowest possible maximum frequency, which we compared to observational constraints on neutron star masses and frequencies. We also compared our findings with the constraints on the tidal deformability obtained in the observations of the GW170817 event. Results. We rule out centrifugal breakup as the mechanism preventing pulsars from spinning faster than f ≈ 700 Hz, as the lowest breakup frequency allowed by our causal equation of state is f ≈ 1200 Hz. A low-frequency cutoff, around f ≈ 800 Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M ≈ 2 M⊙. This would have to be due either to selection effects, or possibly to a phase transition in the interior of the neutron star that leads to softening at high densities and a collapse to either a black hole or a hybrid star above M ≈ 2 M⊙. Such a scenario would, however, require a somewhat unrealistically stiff equation of state for hadronic matter, in tension with recent constraints obtained from gravitational wave observations of a neutron star merger.

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Constraints on Microscopic and Phenomenological Equations of State of Dense Matter from GW170817

Universe ◽

10.3390/universe5100204 ◽

2019 ◽

Vol 5 (10) ◽

pp. 204 ◽

Cited By ~ 1

Author(s):

Domenico Logoteta ◽

Ignazio Bombaci

Keyword(s):

Neutron Star ◽

Neutron Stars ◽

Equations Of State ◽

Mean Field ◽

Dense Matter ◽

Neutron Star Matter ◽

Field Approach ◽

Relativistic Mean Field ◽

Three Body ◽

Good Agreement

We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the β -stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary’s component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data.

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