English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The central speed of sound (SS) measures the stiffness of the Equation ofState (EOS) of superdense neutron star (NS) matter. Its variations with densityand radial coordinate in NSs in conventional analyses often suffer fromuncertainties of the specific nuclear EOSs used. Using the central SS and NSmass/radius scaling obtained from solving perturbatively the scaledTolman-Oppenheimer-Volkoff (TOV) equations, we study the variations of SS,trace anomaly and several closely related properties of NSs in an EOS-modelindependent manner. We find that the SS increases with the reduced centralpressure $\widehat{P}_{\rm{c}}\equiv P_{\rm{c}}/\varepsilon_{\rm{c}}$ (scaledby the central energy density $\varepsilon_{\rm{c}}$), and the conformal boundfor SS tends to break down for NSs with masses higher than about1.9$M_{\odot}$. The ratio $P/\varepsilon$ is upper bounded as$P/\varepsilon\lesssim0.374$ around the centers of stable NSs. We demonstratethat it is an intrinsic property of strong-field gravity and is more relevantthan the perturbative QCD bound on it. While a sharp phase transition at highdensities characterized by a sudden vanishing of SS in cores of massive NSs arebasically excluded, the probability for a continuous crossover signaled by apeaked radial profile of SS is found to be enhanced as $\widehat{P}_{\rm{c}}$decreases, implying it likely happens near the centers of massive NSs.Moreover, a new and more stringent causality boundary as$R_{\max}/\rm{km}\gtrsim 4.73M_{\rm{NS}}^{\max}/M_{\odot}+1.14$ for NS M-Rcurve is found to be excellently consistent with observational data on NSmasses and radii. Furthermore, new constraints on the ultimate energy densityand pressure allowed in NSs before collapsing into black holes are obtained andcompared with earlier predictions in the literature.

Central Speed of Sound, Trace Anomaly and Observables of Neutron Stars from Perturbative Analyses of Scaled TOV Equations