Large and massive neutron stars: Implications for the sound speed within QCD of dense matter

The NASA telescope NICER has recently measured x-ray emissions from the heaviest of precisely known two-solar mass neutron stars, PSR J0740 $+$ 6620. Analysis data [Astrophys. J. Lett. 918, L28 (2021), Astrophys. L27 (2021)] suggests that 6620 a radius in range ${R}_{2.0}\ensuremath{\approx}(11.4--16.1)\phantom{\rule{4pt}{0ex}}\text{km}$ at $68%$ credibility level. In this article, we study implications analysis for sound speed high-density inner cores by using recent chiral effective field theory ($\ensuremath{\chi}\mathrm{EFT}$) calculations equation state next-to-next-to-next-to-leading order to describe outer regions star modest density. We find lower bound on maximum core, $min{{c}_{s,\mathrm{max}}^{2}}$, increases rapidly with massive stars. If $\ensuremath{\chi}\mathrm{EFT}$ remains an efficient expansion nuclear interactions up about twice saturation density, ${R}_{2.0}\ensuremath{\geqslant}13$ km requires $min{{c}_{s,\mathrm{max}}^{2}}\ensuremath{\geqslant}0.562$ and 0.442 68% 95% level, respectively.