Nuclear Physics Multimessenger Astrophysics Constraints on the Neutron Star Equation of State: Adding NICER’s PSR J0740+6620 Measurement

In the past few years, new observations of neutron stars (NSs) and NS mergers have provided a wealth of data that allow one to constrain the equation of state (EOS) of nuclear matter at densities above nuclear saturation density. However, most observations were based on NSs with masses of about 1.4 M ⊙, probing densities up to ∼three to four times the nuclear saturation density. Even higher densities are probed inside massive NSs such as PSR J0740+6620. Very recently, new radio observations provided an update to the mass estimate for PSR J0740+6620, and X-ray observations by the NICER and XMM telescopes constrained its radius. Based on these new measurements, we revisit our previous nuclear physics multimessenger astrophysics constraints and derive updated constraints on the EOS describing the NS interior. By combining astrophysical observations of two radio pulsars, two NICER measurements, the two gravitational-wave detections GW170817 and GW190425, detailed modeling of the kilonova AT 2017gfo, and the gamma-ray burst GRB 170817A, we are able to estimate the radius of a typical 1.4 M ⊙ NS to be 11.94 − 0.87 + 0.76 km at 90% confidence. Our analysis allows us to revisit the upper bound on the maximum mass of NSs and disfavors the presence of a strong first-order phase transition from nuclear matter to exotic forms of matter, such as quark matter, inside NSs.

Temperature and Density Conditions for Alpha Clustering in Excited Self-Conjugate Nuclei

Starting from experimental studies on alpha-clustering in excited self-conjugate nuclei (from 16O to 28Si), temperature and density conditions for such a clustering are determined. Measured temperatures have been found in the range of 5.5–6.0 MeV, whereas density values of 0.3–0.4 times the saturation density are deduced, i.e., 0.046 to 0.062 fm−3. Such a density domain is also predicted by constrained self-consistent mean field calculations. These results constitute a benchmark for alpha clustering from self-conjugate nuclei in relation to descriptions of stellar evolution and supernovae.

Stochastic Thermal Properties of Laminates Filled with Long Fibers

In this paper, the stochastic parameters of the effective thermal conductivity of multilayer composites are considered. The examined specimens of composites were built with a different number of layers and each had a different saturation density of a composite matrix with fibers. For each case of laminate built with a prescribed number of layers and assumed saturation density, 10,000 tests of its effective thermal conductivity were carried out using numerical experiments. It was assumed that the fibers located in each layer were rectilinear, had a circular cross-section and that they could take random positions in their repeatable volume elements (RVEs). In view of the mentioned assumptions, the heat flux passing throughout a cross-section of a composite sample, perpendicular to the fibers’ direction, was considered. The probability density functions were fitted to the obtained data and then the chosen stochastic parameters of the effective thermal conductivity coefficients were determined.

Studying the parameters of the extended σ-ω model for neutron star matter

In this work we study the parameters of the extended σ-ω model for neutron star matter by a Bayesian analysis of state-of-the-art multi-messenger astronomy observations, namely mass, radius and tidal deformabilities. We have considered three parameters of the model, the Landau mass mL, the nuclear compressibility K0, and the value of the symmetry energy S0, all at saturation density n0. As a result, we are able to estimate the best values of the Landau mass of mL ≈ 0.73 GeV, whereas the values of K0 and S0 fall within already known empirical values. Furthermore, for neutron stars we find the most probable value of 13 km < R1.4 < 13.5 km and the upper mass limit of Mmax ≈ 2.2 M⊙.

Effects of symmetry energy on the radius and tidal deformability of neutron stars in the relativistic mean-field model

The radii and tidal deformabilities of neutron stars are investigated in the framework of the relativistic mean-field (RMF) model with different density-dependent behaviors of symmetry energy. To study the effects of symmetry energy on the properties of neutron stars, $\omega$ meson and $\rho$ meson coupling terms are included in a popular RMF Lagrangian, i.e., the TM1 parameter set, which is adopted for the widely used supernova equation of state (EoS) table. The coupling constants relevant to the vector–isovector meson, $\rho$, are refitted by a fixed symmetry energy at subsaturation density and its slope at saturation density, while other coupling constants remain the same as the original ones in TM1 so as to update the supernova EoS table. The radius and mass of maximum neutron stars are not so sensitive to the symmetry energy in these family TM1 parameterizations. However, the radii in the intermediate-mass region are strongly correlated with the slope of symmetry energy. Furthermore, the dimensionless tidal deformabilities of neutron stars are also calculated within the associated Love number, which is related to the quadrupole deformation of the star in a static external tidal field and can be extracted from the observation of a gravitational wave generated by a binary star merger. We find that its value at $1.4 \mathrm{M}_\odot$ has a linear correlation to the slope of symmetry energy, unlike that previously studied. With the latest constraints of tidal deformabilities from the GW170817 event, the slope of symmetry energy at nuclear saturation density should be smaller than $60$ MeV in the family TM1 parameterizations. This fact supports the usage of a lower symmetry energy slope for the updated supernova EoS, which is applicable to simulations of neutron star mergers. Furthermore, an analogous analysis is also done within the family IUFSU parameter sets. It is found that the correlations between the symmetry energy slope with the radius and tidal deformability at $1.4 \mathrm{M}_\odot$ have very similar linear relations in these RMF models.

Neutron Star Mass and Radius Measurements

Constraints on neutron star masses and radii now come from a variety of sources: theoretical and experimental nuclear physics, astrophysical observations including pulsar timing, thermal and bursting X-ray sources, and gravitational waves, and the assumptions inherent to general relativity and causality of the equation of state. These measurements and assumptions also result in restrictions on the dense matter equation of state. The two most important structural parameters of neutron stars are their typical radii, which impacts intermediate densities in the range of one to two times the nuclear saturation density, and the maximum mass, which impacts the densities beyond about three times the saturation density. Especially intriguing has been the multi-messenger event GW170817, the first observed binary neutron star merger, which provided direct estimates of both stellar masses and radii as well as an upper bound to the maximum mass.

Transcript profile distinguishes variability in human myogenic progenitor cell expansion capacity

Primary human muscle progenitor cells (hMPCs) are commonly used to understand skeletal muscle biology, including the regenerative process. Variability from unknown origin in hMPC expansion capacity occurs independently of disease, age, or sex of the donor. We sought to determine the transcript profile that distinguishes hMPC cultures with greater expansion capacity and to identify biological underpinnings of these transcriptome profile differences. Sorted (CD56+/CD29+) hMPC cultures were clustered by unbiased, K-means cluster analysis into FAST and SLOW based on growth parameters (saturation density and population doubling time). FAST had greater expansion capacity indicated by significantly reduced population doubling time (−60%) and greater saturation density (+200%), nuclei area under the curve (AUC, +250%), and confluence AUC (+120%). Additionally, FAST had fewer % dead cells AUC (−44%, P < 0.05). RNA sequencing was conducted on RNA extracted during the expansion phase. Principal component analysis distinguished FAST and SLOW based on the transcript profiles. There were 2,205 differentially expressed genes (DEgenes) between FAST and SLOW (q value ≤ 0.05); 362 DEgenes met a more stringent cut-off (q value ≤ 0.001 and 2.0 fold-change). DEgene enrichment suggested FAST (vs. SLOW) had promotion of the cell cycle, reduced apoptosis and cellular senescence, and enhanced DNA replication. Novel (RABL6, IRGM1, and AREG) and known (FOXM1, CDKN1A, Rb) genes emerged as regulators of identified functional pathways. Collectively the data suggest that variation in hMPC expansion capacity occurs independently of age and sex and is driven, in part, by intrinsic mechanisms that support the cell cycle.