Neutron Star Equation of State in Light of GW190814

Tan, Hung; Noronha-Hostler, Jacquelyn; Yunes, Nicolás

doi:10.1103/physrevlett.125.261104

Cited by 140 publications

(95 citation statements)

References 78 publications

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“…On the other hand, the possibility for GW190814's secondary as a neutron star can be accomplished by: (1) choosing/constructing stiff EOSs having a maximum mass larger than 2.5 M [76,[141][142][143][144][145][146][147][148][149][150]; (2) considering the effects of fast rotations, which can increase the maximum mass by about 20% when a star rotates at the Kepler frequency (the maximum frequency at which the gravitational attraction is still sufficient to keep matter bound to the pulsar surface) [42,43,139,140,145,[151][152][153][154][155][156][157] ; (3) considering other effects/models that can modify the maximum mass of a neutron star, such as the magnetic field [147], twin star [158], two families of compact stars [142], finite temperature [153], antikaon condensation [159], net electric charge [144], etc.…”

Section: Is Gw190814's Secondary a Superfast And Supermassive Neutron Star Or Something Else?mentioning

confidence: 99%

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

Cai²,

Wang

et al. 2021

Universe

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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Section: Is Gw190814's Secondary a Superfast And Supermassive Neutron Star Or Something Else?mentioning

confidence: 99%

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

Cai²,

Wang

et al. 2021

Universe

137

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“…Tidal effects are quantified through the dimensionless tidal deformability Λ, which scales roughly as ðR=mÞ 6 [26] for a NS of mass m and radius R, implying that the most massive-and thus most compact-NSs exhibit inherently weaker tidal interactions. As an result, the very nature of some ∼2-3 M ⊙ compact objects observed with GWs, such as the primary in GW190425 [27] and the secondary in GW190814 [28], cannot be determined beyond a reasonable doubt [29][30][31][32][33][34]. In the same density regime as the GWs, the electromagnetic counterpart to GW170817 may bound the EoS stiffness from below [35][36][37][38], though it is subject to significant systematic modeling uncertainty [39,40].…”

Section: Introductionmentioning

confidence: 99%

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

et al. 2021

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X-ray pulse profile modeling of PSR J0740 þ 6620, the most massive known pulsar, with data from the NICER and XMM-Newton observatories recently led to a measurement of its radius. We investigate this measurement's implications for the neutron star equation of state (EoS), employing a nonparametric EoS model based on Gaussian processes and combining information from other x-ray, radio and gravitationalwave observations of neutron stars. Our analysis mildly disfavors EoSs that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of 6.9. For such EoSs, the transition mass from the hadronic to the hybrid branch is constrained to lie outside ð1; 2Þ M ⊙ . We also find that the conformal sound-speed bound is violated inside neutron star cores, which implies that the core matter is strongly interacting. The squared sound speed reaches a maximum of 0.75 þ0.25 −0.24 c 2 at 3.60 þ2.25 −1.89 times nuclear saturation density at 90% credibility. Since all but the gravitational-wave observations prefer a relatively stiff EoS, PSR J0740 þ 6620's central density is only 3.57 þ1.3 −1.3 times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in β-equilibrium.

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“…Furthermore, we highlight the very recent observation of the GW190814 event, where a gravitational wave has been detected from the merger of a 22.2-24.3 M black hole with a non-identified compact object with mass 2.5-2.67 M [19,20]. Although the authors of the mentioned references suggest that is unlikely for the second component's mass to belong to a neutron star, they do leave open the window that the improved knowledge of the neutron star EoS and further observations of the astrophysical population of compact objects could alter this assessment.…”

Section: Introductionmentioning

confidence: 77%

“…By subtracting the component masses m 1 , m 2 in Equation ( 18), we obtain the corresponding values of M c . Then, since the masses are defined, from the Equations ( 19) and (20), the effective tidal deformability Λ can be determined.…”

Section: A Very Massive Neutron Star In a Binary Neutron Stars Systemmentioning

confidence: 99%

Neutron Stars and Gravitational Waves: The Key Role of Nuclear Equation of State

Koliogiannis¹,

Kanakis-Pegios²,

Moustakidis³

2021

Foundations

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Neutron stars are the densest known objects in the universe and an ideal laboratory for the strange physics of super-condensed matter. Theoretical studies in connection with recent observational data of isolated neutron stars, as well as binary neutron stars systems, offer an excellent opportunity to provide robust solutions on the dense nuclear problem. In the present work, we review recent studies concerning the applications of various theoretical nuclear models on a few recent observations of binary neutron stars or neutron-star–black-hole systems. In particular, using a simple and well-established model, we parametrize the stiffness of the equation of state with the help of the speed of sound. Moreover, in comparison to the recent observations of two events by LIGO/VIRGO collaboration, GW170817 and GW190425, we suggest possible robust constraints. We also concentrate our theoretical study on the resent observation of a compact object with mass ∼2.59−0.09+0.08M⊙ (GW190814 event), as a component of a system where the main companion was a black hole with mass ∼23M⊙. There is scientific debate concerning the identification of the low mass component, as it falls into the neutron-star–black-hole mass gap. This is an important issue since understanding the nature of GW190814 event will offer rich information concerning the upper limit of the speed of sound in dense matter and the possible phase transition into other degrees of freedom. We systematically study the tidal deformability of a possible high-mass candidate existing as an individual star or as a component in a binary neutron star system. Finally, we provide some applications of equations of state of hot, dense nuclear matter in hot neutron stars (nonrotating and rapidly rotating with the Kepler frequency neutron stars), protoneutron stars, and binary neutron star merger remnants.

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Neutron Star Equation of State in Light of GW190814

Cited by 140 publications

References 78 publications

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

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

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

Neutron Stars and Gravitational Waves: The Key Role of Nuclear Equation of State

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