Limiting masses and radii of neutron stars and their implications
Abstract
We combine the equation of state of dense matter up to twice nuclear saturation density n_{sat} obtained using chiral effective field theory (χ EFT ) and recent observations of neutron stars to gain insights about the highdensity matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on orderbyorder calculations up to nexttonexttonexttoleading order in the χ EFT expansion. We refine the bounds on the maximum mass imposed by causality at high densities and provide stringent limits on the maximum and minimum radii of ∼1.4 M_{⊙} and ∼2.0 M_{⊙} stars. Including χ EFT predictions from n_{sat} to 2 n_{sat} reduces the permitted ranges of the radius of a 1.4 M_{⊙} star, R_{1.4}, by ∼3.5 km . If observations indicate R_{1.4}<11.2 km , then our study implies that either the squared speed of sound c_{s}^{2}>1 /2 for densities above 2 n_{sat} or that χ EFT breaks down below 2 n_{sat} . We also comment on the nature of the secondary compact object in GW190814 with mass ≃2.6 M_{⊙} and discuss the implications of massive neutron stars >2.1 M_{⊙}(2.6 M_{⊙}) in future radio and gravitationalwave searches. Some form of strongly interacting matter with c_{s}^{2}>0.35 (0.55 ) must be realized in the cores of such massive neutron stars. In the absence of phase transitions below 2 n_{sat} , the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by χ EFT for the baryon density n_{B} in the range 1 2 n_{sat} . Together they imply that the rapid stiffening required to support a high maximum mass should occur only when n_{B}≳1.5 1.8 n_{sat} .
 Publication:

Physical Review C
 Pub Date:
 April 2021
 DOI:
 10.1103/PhysRevC.103.045808
 arXiv:
 arXiv:2009.06441
 Bibcode:
 2021PhRvC.103d5808D
 Keywords:

 Nuclear Theory;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 26 pages, 17 figures