Bayesian Inference of High-density Nuclear Symmetry Energy from Radii of Canonical Neutron Stars

Wang, Xie; Li, Bao-An

doi:10.3847/1538-4357/ab3f37

Cited by 110 publications

(106 citation statements)

References 116 publications

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“…Various studies have empirically identified correlations between various combinations of parameters that characterize the symmetry energy and its density dependence with the neutron star radius and tidal parameters [246,[266][267][268][269] or terrestrial experimental results [239,[270][271][272], as they all are linked to the low-density behavior of the equation of state around (twice) saturation. The tidal constraints from GW170817, and more recently radius constraints from NICER have been used to examine implications for the symmetry energy [273][274][275][276][277][278][279][280][281][282] as well as potential systematics in the mapping [283].…”

Section: Microscopic Propertiesmentioning

confidence: 99%

Neutron-star tidal deformability and equation-of-state constraints

2020

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Despite their long history and astrophysical importance, some of the key properties of neutron stars are still uncertain. The extreme conditions encountered in their interiors, involving matter of uncertain composition at extreme density and isospin asymmetry, uniquely determine the stars' macroscopic properties within General Relativity. Astrophysical constraints on those macroscopic properties, such as neutron star masses and radii, have long been used to understand the microscopic properties of the matter that forms them. In this article we discuss another astrophysically observable macroscopic property of neutron stars that can be used to study their interiors: their tidal deformation. Neutron stars, much like any other extended object with structure, are tidally deformed when under the influence of an external tidal field. In the context of coalescences of neutron stars observed through their gravitational wave emission, this deformation, quantified through a parameter termed the tidal deformability, can be measured. We discuss the role of the tidal deformability in observations of coalescing neutron stars with gravitational waves and how it can be used to probe the internal structure of Nature's most compact matter objects. Perhaps inevitably, a large portion of the discussion will be dictated by GW170817, the most informative confirmed detection of a binary neutron star coalescence with gravitational waves as of the time of writing.

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Section: Microscopic Propertiesmentioning

confidence: 99%

Neutron-star tidal deformability and equation-of-state constraints

2020

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“…As an example, shown in Figure 3 is the magnitude of symmetry energy at twice the saturation density of nuclear matter from nine recent analyses of neutron stars in comparison with the two results from earlier heavy-ion reaction experiments (from the FOPI-LAND [93] and the ASY-EOS [94] Collaborations by analyzing the relative flows and yields of light mirror nuclei, as well as neutrons and protons in heavy-ion collisions at beam energies of 400 MeV/nucleon). More specifically, the nine analyses were from (1) (Zhang and Li 2019) directly inverting observed NS radii, tidal deformability, and maximum mass in the high-density EOS space [95][96][97], (2) (Xie and Li 2019) a Bayesian inference from the radii of canonical NSs observed by using Chandra X-rays and gravitational waves from GW170817 [98] While certainly the model dependence and the error bars are still relatively large, all results from both heavy-ion reactions and neutron stars scatter around an overall mean of E sym (2ρ 0 ) ≈ 51 ± 13 MeV at a 68% confidence level, as indicated by the green line. The symmetry energy around 2ρ 0 is particularly interesting because the pressure around this density determines the radii of canonical NSs [5].…”

Section: Symmetry Energy At 2ρ 0 Extracted From Neutron Star Observablesmentioning

confidence: 99%

Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817

Cai²,

Wang

et al. 2021

Universe

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137

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The density dependence of nuclear symmetry energy is among the most uncertain parts of the Equation of State (EOS) of dense neutron-rich nuclear matter. It is currently poorly known especially at suprasaturation densities partially because of our poor knowledge about isovector nuclear interactions at short distances. Because of its broad impacts on many interesting issues, pinning down the density dependence of nuclear symmetry energy has been a longstanding and shared goal of both astrophysics and nuclear physics. New observational data of neutron stars including their masses, radii, and tidal deformations since GW170817 have helped improve our knowledge about nuclear symmetry energy, especially at high densities. Based on various model analyses of these new data by many people in the nuclear astrophysics community, while our brief review might be incomplete and biased unintentionally, we learned in particular the following: (1) The slope parameter L of nuclear symmetry energy at saturation density ρ0 of nuclear matter from 24 new analyses of neutron star observables was about L≈57.7±19 MeV at a 68% confidence level, consistent with its fiducial value from surveys of over 50 earlier analyses of both terrestrial and astrophysical data within error bars. (2) The curvature Ksym of nuclear symmetry energy at ρ0 from 16 new analyses of neutron star observables was about Ksym≈−107±88 MeV at a 68% confidence level, in very good agreement with the systematics of earlier analyses. (3) The magnitude of nuclear symmetry energy at 2ρ0, i.e., Esym(2ρ0)≈51±13 MeV at a 68% confidence level, was extracted from nine new analyses of neutron star observables, consistent with the results from earlier analyses of heavy-ion reactions and the latest predictions of the state-of-the-art nuclear many-body theories. (4) While the available data from canonical neutron stars did not provide tight constraints on nuclear symmetry energy at densities above about 2ρ0, the lower radius boundary R2.01=12.2 km from NICER’s very recent observation of PSR J0740+6620 of mass 2.08±0.07M⊙ and radius R=12.2–16.3 km at a 68% confidence level set a tight lower limit for nuclear symmetry energy at densities above 2ρ0. (5) Bayesian inferences of nuclear symmetry energy using models encapsulating a first-order hadron–quark phase transition from observables of canonical neutron stars indicated that the phase transition shifted appreciably both L and Ksym to higher values, but with larger uncertainties compared to analyses assuming no such phase transition. (6) The high-density behavior of nuclear symmetry energy significantly affected the minimum frequency necessary to rotationally support GW190814’s secondary component of mass (2.50–2.67) M⊙ as the fastest and most massive pulsar discovered so far. Overall, thanks to the hard work of many people in the astrophysics and nuclear physics community, new data of neutron star observations since the discovery of GW170817 have significantly enriched our knowledge about the symmetry energy of dense neutron-rich nuclear matter.

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“…(Zhang et al 2018;Zhang & Li 2019a), one can examine how each NS observable may help constrain the high-density EOS parameter space. We note that results from the direct inversion and statistical inversion using the Bayesian approach were found consistent (Xie & Li 2019). As examples relevant for the present study, shown in Figure 4 are the constant surfaces of several observables and physics conditions in the 3D K sym −J sym −J 0 EOS parameter space: the NS maximum mass of M=2.14 M ⊙ (green surface) or 2.01 M ⊙ (pink surface), the radius of canonical NS R 1.4 = 12.83 km (yellow surface) or R 1.28 = 11.52 km (orange surface) for a NS of mass 1.28 M ⊙ , the dimensionless tidal deformability of canonical NS Λ 1.4 = 580 (red surface), and the causality surface (blue) on which the speed of sound equals the speed of light at the central density of the most massive NS supported by the nuclear pressure at each point with the specific EOS there (Zhang & Li 2019a).…”

Section: Observational Constraints On the High-density Eos Parameter mentioning

confidence: 56%

“…Indeed, observations of NSs using several different kinds of messengers in recent years have already provided some useful constraints on the high-density EOS. Within the model framework discussed above, we have recently studied how the three high-density EOS parameters are constrained by NS observations (Zhang et al 2018;Zhang & Li 2019a,b,c;Xie & Li 2019). These include the radii R 1.4 of canonical NSs, e.g., 10.62 < R 1.4 < 12.83 km from analyzing quiescent low-mass X-ray binaries (Lattimer & Steiner 2014), the dimensionless tidal deformability 70 ≤ Λ 1.4 ≤ 580 from the refined analysis of GW170817 data (Abbott et al 2018), and the latest NS maximum mass M = 2.14 +0.10 −0.09 M ⊙ from the observations of PSR J0740+6620 (Cromartie et al 2019).…”

Section: Observational Constraints On the High-density Eos Parameter mentioning

confidence: 99%

Constraints on the Muon Fraction and Density Profile in Neutron Stars

Zhang

2020

ApJ

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Muons in neutron stars (NSs) play especially important roles in addressing several interesting new physics questions associated with detecting as well as understanding interactions and astrophysical effects of muonphilic dark matter particles. The key model inputs for studying the latter are the total muon mass M µ , the muon mass fraction M µ /M NS over the NS mass M NS and the muon radial density profile ρ µ (r) in NSs of varying masses. We investigate these quantities within a minimum model for the core of NSs consisting of neutrons, protons, electrons, and muons using an explicitly isospin-dependent parametric Equation of State (EOS) constrained by available nuclear laboratory experiments and the latest astrophysical observations of NS masses, radii and tidal deformabilities. We found that the absolutely maximum muon mass M µ and its mass fraction M µ /M NS in the most massive NSs allowed by causality are about 0.025 M ⊙ and 1.1%, respectively. For the most massive NS of mass 2.14 M ⊙ observed so far, they reduce to about 0.020 M ⊙ and 0.9%, respectively. We also study respective effects of individual parameters describing the EOS of high-density neutron-rich nucleonic matter on the muon contents in NSs with varying masses. We found that the most important but uncertain nuclear physics ingredient for determining the muon contents in NSs is the high-density nuclear symmetry energy. Keywords: Dense matter, equation of state, stars: neutron 9 12 15 J sym =200 J 0 =200 M NS [M sun ] K sym =100 K sym =0 K sym =-100 K sym =100 J 0 =200 J sym =800 J sym =600 J sym =400 J 0 =400 J 0 =200 J 0 =0 K sym =100 J sym =200 K sym =-200 K sym =-300 M m [M sun ] J sym =200 J sym =0 J sym =-200 J 0 ] J sym =800 J sym =600 J sym =400 J sym =200 J sym =0 J sym =-200 K sym =100 J sym =200 J 0 =400 J 0 =200 J 0 =0 J 0 =-100 J 0 =-200

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Bayesian Inference of High-density Nuclear Symmetry Energy from Radii of Canonical Neutron Stars

Cited by 110 publications

References 116 publications

Neutron-star tidal deformability and equation-of-state constraints

Neutron-star tidal deformability and equation-of-state constraints

Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817

Constraints on the Muon Fraction and Density Profile in Neutron Stars

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