Limiting masses and radii of neutron stars and their implications

Christian Drischler; Sophia Han; James M. Lattimer; Madappa Prakash; Sanjay Reddy; Tianqi Zhao

doi:10.1103/PhysRevC.103.045808

paper

Limiting masses and radii of neutron stars and their implications

arXiv:2009.06441 · doi:10.1103/PhysRevC.103.045808

Abstract

We combine equation of state of dense matter up to twice nuclear saturation density ( $n_{sat} = 0.16 fm^{- 3}$ ) obtained using chiral effective field theory ( $χ$ EFT), and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading 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 $\sim 1.4 M_{⊙}$ and $\sim 2.0 M_{⊙}$ 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 $\sim 3.5 km$ . If observations indicate $R_{1.4} < 11.2 km$ , 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 gravitational-wave 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 $n_{B} ≳ 1.5 - 1.8 n_{sat}$ .

arXiv comment26 pages, 17 figures; accepted for publication in PRC, appendices and references updated

Limiting masses and radii of neutron stars and their implications

Abstract

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