Large and massive neutron stars: Implications for the sound speed in dense QCD
Abstract
The NASA telescope NICER has recently measured xray emissions from the heaviest of the precisely known twosolar mass neutron stars, PSR J0740+6620. Analysis of the data [Miller et al., Astrophys. J. Lett. 918, L28 (2021); Riley et al., Astrophys. J. Lett. 918, L27 (2021)] suggests that PSR J0740+6620 has a radius in the range of $R_{2.0} \approx (11.416.1)$ km at the $68\%$ credibility level. In this article, we study the implications of this analysis for the sound speed in the highdensity inner cores by using recent chiral effective field theory ($\chi$EFT) calculations of the equation of state at nexttonexttonexttoleading order to describe outer regions of the star at modest density. We find that the lower bound on the maximum speed of sound in the inner core, $\textbf{min}\{c^2_{s, {\rm max}}\}$, increases rapidly with the radius of massive neutron stars. If $\chi$EFT remains an efficient expansion for nuclear interactions up to about twice the nuclear saturation density, $R_{2.0}\geqslant 13$ km requires $\textbf{min}\{c^2_{s, {\rm max}}\} \geqslant 0.562$ and $0.442$ at the $68\%$ and $95\%$ credibility level, respectively.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 arXiv:
 arXiv:2110.14896
 Bibcode:
 2021arXiv211014896D
 Keywords:

 Nuclear Theory;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 10 pages, 6 figures