Imprint of the speed of sound in nuclear matter on global properties of neutron stars

Na Zhang, Dehua Wen, and Houyuan Chen
Phys. Rev. C 99, 035803 – Published 15 March 2019

Abstract

Internal structure and macroscopic properties of neutron stars are strongly correlated with the equation of state (EOS) of dense matter, while the EOS remains exceedingly uncertain especially at high densities. The observed massive neutron star with gravitation mass of 2M have imposed strong constraints on the EOS of super-dense matter. The upper limit of the speed of sound, as a crucial quantity to characterize the stiffness of the EOS, has significant influence on the maximum mass of a neutron star. The main propose of this work is to probe the possible lower bound for the upper limit of the speed of sound, where being coincident with the observations for massive neutron stars is considered. By employing a set of heterogeneous EOSs and through a constructed EOS model to describe the high-density part of the employed EOSs, we conclude that the upper limit of the speed of sound can be as low as 0.5386 c (where c is the speed of light). Furthermore, to eliminate the effect of the model dependence for the EOSs, we adopt a set of parameterized and model-independent EOSs to investigate this problem. As a result, a lower bound 0.5749 c of the upper limit of the speed of sound is obtained, which is very close to the free-quark-matter's speed of sound, 13c. In addition, we semiempirically analyze the characteristics of the profile of neutron star MR relations and find out that the profiles of MR relations mainly depend on the speed of sound of the central density of neutron star sequences in the mass range around 0.3to1M. However, the MR profile also can be explained by the universal relation proposed by Lattimer et al. Astroph. J. 550, 426 (2001), where the case with extremely soft EOS in ρ0to2ρ0 should be excluded.

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  • Received 3 September 2018
  • Revised 9 December 2018

DOI:https://doi.org/10.1103/PhysRevC.99.035803

©2019 American Physical Society

Physics Subject Headings (PhySH)

Nuclear PhysicsGravitation, Cosmology & Astrophysics

Authors & Affiliations

Na Zhang, Dehua Wen*, and Houyuan Chen

  • School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, People's Republic of China

  • *wendehua@scut.edu.cn

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Issue

Vol. 99, Iss. 3 — March 2019

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