Viscous neutron stars have new families of axial oscillation modes without perfect-fluid counterparts, featuring mode avoidance and long-lived modes.
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The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
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abstract
PSR J0740$+$6620 has a gravitational mass of $2.08\pm 0.07~M_\odot$, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740$+$6620 is $13.7^{+2.6}_{-1.5}$ km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030$+$0451, the masses of two other $\sim 2~M_\odot$ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation of state modeling, and find consistent results at $\sim 1.5-3$ times nuclear saturation density. For a given framework, when all measurements are included the radius of a $1.4~M_\odot$ neutron star is known to $\pm 4$% (68% credibility) and the radius of a $2.08~M_\odot$ neutron star is known to $\pm 5$%. The full radius range that spans the $\pm 1\sigma$ credible intervals of all the radius estimates in the three frameworks is $12.45\pm 0.65$ km for a $1.4~M_\odot$ neutron star and $12.35\pm 0.75$ km for a $2.08~M_\odot$ neutron star.
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A redefinition of the symmetry energy expansion that incorporates finite strangeness consistent with SU(3) flavor symmetry and remains valid beyond typical neutron-star central densities.
A conservative f(R,T) gravity reformulation decouples the gravitational sector from the microphysical equation of state, enabling computation of neutron star mass-radius relations and tidal deformabilities that satisfy current astrophysical constraints.
Emulator-assisted Bayesian inference of an extended Skyrme EDF, jointly constrained by nuclear observables, ab initio calculations, and NICER data, produces posteriors yielding consistent neutron star crust and core properties with a provided multivariate Gaussian for bulk nuclear matter parameters.
New quasi-universal relations connect static tidal deformability Λ⁰ to its dynamical correction Λ² and to Mω* with equation-of-state scatter below 5% and 2.8% respectively across 59 models.
Bayesian NS EoS study using full nuclear posterior distributions and consistent crust modeling finds increased surface thickness and crustal moment of inertia relative to prior work.
Joint NICER+IXPE pulse-profile modeling of SRGA J144459.2-604207 favors large neutron-star mass and radius with two independent hotspots but shows strong sensitivity to joint-analysis methodology.
NLED alters photon propagation near magnetars, producing ~10% errors in inferred radii via ray-tracing and a minimal ~350 ns travel-time delay.
Bayesian analysis finds that the likely ranges of light dark-matter fermion mass and exponential density-profile parameter in hyperon-containing neutron stars are nearly independent of the hadronic model for symmetry-energy slopes between 40 and 58 MeV, with HESS J1731-347 and GW170817 data playing,
Axial modes of anisotropic neutron stars show mass-scaled frequency and damping time with nearly universal quadratic dependence on compactness, insensitive to EOS and anisotropy model.
Hybrid star model with core quark pasta pinning superfluid vortices produces glitch amplitudes ΔΩ/Ω of order 10^{-6} matching Vela-like pulsar observations.
Hybrid neutron-star equations of state remain sensitive to the low-density nucleonic model at transition densities around 2ρ₀, with model spread in radius and tidal deformability exceeding observational uncertainty by factors of ~1.8 and ~1.4.
Vector portal fermionic dark matter admixed in neutron stars produces mediator-mass-dependent changes to the equation of state, yielding distinct mass-radius relations and tidal deformabilities that observations can use to constrain the model.
Roughly half of realistic neutron-star equations of state produce stars with negative Ricci scalar inside, and an improved analytic fit links gravitational mass M to baryonic mass Mb with maximum 3 percent variance.
Holographic model of massive deconfined quarks yields a stiff enough equation of state to allow stable 2-solar-mass hybrid stars with quark cores for certain nuclear phases.
Rotation amplifies differences between the vector MIT bag and DDQM equations of state for quark stars, with MIT supporting more massive stars and a full decomposition of gravitational, internal, rotational, and binding energies provided.
Quasi-universal relations connect the trace anomaly profile of neutron star matter to stellar compactness, moment of inertia, and tidal deformability, yielding a central value estimate of Δ_c = 0.1770^{+0.0365}_{-0.0432} for a 1.4 M_⊙ star.
Dark matter cores heat baryonic matter in evolving proto-neutron stars by deepening the gravitational potential while halos cool it, providing a diagnostic distinct from hyperons.
A small vacuum-like dark-energy admixture in neutron stars with 400 MeV–1 GeV fermionic dark matter shrinks halo-induced radius differences from several kilometers to sub-kilometer scales and mass differences to ≲1%.
The study examines the effects of hyperons and H-dibaryons on f-mode oscillations in neutron stars using the quark meson coupling model and tests universal relations in the Cowling approximation.
The quark-hadron mixed phase width in hybrid stars is mainly controlled by effective nucleon mass and symmetry energy, with temperature reducing the width and softening the EOS while strong vector repulsion is needed to match massive pulsar and NICER data.
A Poincaré-covariant vector-vector contact interaction yields an equation of state for strange quark matter whose mass-radius and tidal properties match pulsar and gravitational-wave constraints for two tuned parameter sets.
Interacting vacuum energy relaxes the pressure gradient inside stars, allowing finite central pressure and compactness beyond the Buchdahl bound for suitable coupling strengths.
Moderate positive pressure anisotropy raises neutron star maximum mass to about 2.4 solar masses and compactness by up to 20 percent, with curvature scalars tied to matter showing strong sensitivity while the Weyl scalar stays largely insensitive.
citing papers explorer
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Axial Oscillations of Viscous Neutron Stars
Viscous neutron stars have new families of axial oscillation modes without perfect-fluid counterparts, featuring mode avoidance and long-lived modes.
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Symmetry Energy Expansion with Strange Dense Matter
A redefinition of the symmetry energy expansion that incorporates finite strangeness consistent with SU(3) flavor symmetry and remains valid beyond typical neutron-star central densities.
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Neutron stars in a conservative $f(R,T)$ gravity
A conservative f(R,T) gravity reformulation decouples the gravitational sector from the microphysical equation of state, enabling computation of neutron star mass-radius relations and tidal deformabilities that satisfy current astrophysical constraints.
-
Emulator-Assisted Nuclear DFT Inference and Its Consequences for the Structure of Neutron Stars
Emulator-assisted Bayesian inference of an extended Skyrme EDF, jointly constrained by nuclear observables, ab initio calculations, and NICER data, produces posteriors yielding consistent neutron star crust and core properties with a provided multivariate Gaussian for bulk nuclear matter parameters.
-
Universal Relations with Dynamical Tides
New quasi-universal relations connect static tidal deformability Λ⁰ to its dynamical correction Λ² and to Mω* with equation-of-state scatter below 5% and 2.8% respectively across 59 models.
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Properties of the neutron star crust informed by nuclear structure data
Bayesian NS EoS study using full nuclear posterior distributions and consistent crust modeling finds increased surface thickness and crustal moment of inertia relative to prior work.
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Pulse profile modelling of the 2024 outburst of the accreting millisecond pulsar SRGA J144459.2-604207
Joint NICER+IXPE pulse-profile modeling of SRGA J144459.2-604207 favors large neutron-star mass and radius with two independent hotspots but shows strong sensitivity to joint-analysis methodology.
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Nonlinear electrodynamics in magnetars: systematic effects on radius constraints and timing analysis
NLED alters photon propagation near magnetars, producing ~10% errors in inferred radii via ray-tracing and a minimal ~350 ns travel-time delay.
-
Bayesian analysis of density profile of light dark matter elucidating the properties of dark matter admixed neutron stars in the presence of hyperons
Bayesian analysis finds that the likely ranges of light dark-matter fermion mass and exponential density-profile parameter in hyperon-containing neutron stars are nearly independent of the hadronic model for symmetry-energy slopes between 40 and 58 MeV, with HESS J1731-347 and GW170817 data playing,
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On the non-radial oscillations of realistic anisotropic neutron stars: Axial modes
Axial modes of anisotropic neutron stars show mass-scaled frequency and damping time with nearly universal quadratic dependence on compactness, insensitive to EOS and anisotropy model.
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Modeling large glitches with core superfluidity in a Hybrid star
Hybrid star model with core quark pasta pinning superfluid vortices produces glitch amplitudes ΔΩ/Ω of order 10^{-6} matching Vela-like pulsar observations.
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Sensitivity of Neutron Star Observables to Transition Density in Hybrid Equation-of-State Models
Hybrid neutron-star equations of state remain sensitive to the low-density nucleonic model at transition densities around 2ρ₀, with model spread in radius and tidal deformability exceeding observational uncertainty by factors of ~1.8 and ~1.4.
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Neutron star with dark matter using vector portal
Vector portal fermionic dark matter admixed in neutron stars produces mediator-mass-dependent changes to the equation of state, yielding distinct mass-radius relations and tidal deformabilities that observations can use to constrain the model.
-
General gravitational properties of neutron stars: curvature invariants, binding energy, and trace anomaly
Roughly half of realistic neutron-star equations of state produce stars with negative Ricci scalar inside, and an improved analytic fit links gravitational mass M to baryonic mass Mb with maximum 3 percent variance.
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Properties of Stable Massive Quark Stars in Holography
Holographic model of massive deconfined quarks yields a stiff enough equation of state to allow stable 2-solar-mass hybrid stars with quark cores for certain nuclear phases.
-
Rotational effects in quark stars: comparing different models
Rotation amplifies differences between the vector MIT bag and DDQM equations of state for quark stars, with MIT supporting more massive stars and a full decomposition of gravitational, internal, rotational, and binding energies provided.
-
Tracing the Trace Anomaly of Dense Matter inside Neutron Stars
Quasi-universal relations connect the trace anomaly profile of neutron star matter to stellar compactness, moment of inertia, and tidal deformability, yielding a central value estimate of Δ_c = 0.1770^{+0.0365}_{-0.0432} for a 1.4 M_⊙ star.
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Dark Matter Heating in Evolving Proto-Neutron Stars: A Two-Fluid Approach
Dark matter cores heat baryonic matter in evolving proto-neutron stars by deepening the gravitational potential while halos cool it, providing a diagnostic distinct from hyperons.
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Sub-GeV dark matter in neutron stars: halo morphologies and their suppression by vacuum-like pressure
A small vacuum-like dark-energy admixture in neutron stars with 400 MeV–1 GeV fermionic dark matter shrinks halo-induced radius differences from several kilometers to sub-kilometer scales and mass differences to ≲1%.
-
$f$-mode Oscillations for Hyperons and H-dibaryons in Neutron Stars
The study examines the effects of hyperons and H-dibaryons on f-mode oscillations in neutron stars using the quark meson coupling model and tests universal relations in the Cowling approximation.
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Characterizing the quark-hadron mixed phase in compact star cores : sensitivity to nuclear saturation and quark-model parameters at finite-temperature
The quark-hadron mixed phase width in hybrid stars is mainly controlled by effective nucleon mass and symmetry energy, with temperature reducing the width and softening the EOS while strong vector repulsion is needed to match massive pulsar and NICER data.
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A Poincar\'e-covariant study of strange quark stars
A Poincaré-covariant vector-vector contact interaction yields an equation of state for strange quark matter whose mass-radius and tidal properties match pulsar and gravitational-wave constraints for two tuned parameter sets.
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Buchdahl Limit and TOV Equations in Interacting Vacuum Scenarios
Interacting vacuum energy relaxes the pressure gradient inside stars, allowing finite central pressure and compactness beyond the Buchdahl bound for suitable coupling strengths.
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Impact of Anisotropy on Neutron Star Structure and Curvature
Moderate positive pressure anisotropy raises neutron star maximum mass to about 2.4 solar masses and compactness by up to 20 percent, with curvature scalars tied to matter showing strong sensitivity while the Weyl scalar stays largely insensitive.
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Equation of State Extrapolation Systematics: Parametric vs. Nonparametric Inference of Neutron Star Structure
Nonparametric GP-based high-density extensions yield softer EOS posteriors with larger uncertainties than parametric PP extensions when jointly constrained by multi-messenger neutron star observations.
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Spin effects in superfluidity, neutron matter and neutron stars
A review of spin effects, superfluidity, and magnetic fields in neutron matter and their influence on neutron-star structure, superfluid phases, and rotational dynamics.