A General, Scale-independent Description of the Sound Speed in Neutron Stars

Ecker, Christian and Rezzolla, Luciano (2022) A General, Scale-independent Description of the Sound Speed in Neutron Stars. The Astrophysical Journal Letters, 939 (2). L35. ISSN 2041-8205

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Abstract

Using more than a million randomly generated equations of state that satisfy theoretical and observational constraints, we construct a novel, scale-independent description of the sound speed in neutron stars, where the latter is expressed in a unit cube spanning the normalized radius, r/R, and the mass normalized to the maximum one, M/MTOV. From this generic representation, a number of interesting and surprising results can be deduced. In particular, we find that light (heavy) stars have stiff (soft) cores and soft (stiff) outer layers, or that the maximum of the sound speed is located at the center of light stars but moves to the outer layers for stars with M/MTOV ≳ 0.7, reaching a constant value of ${c}_{s}^{2}\,=\,1/2$ as M → MTOV. We also show that the sound speed decreases below the conformal limit ${c}_{s}^{2}\,=\,1/3$ at the center of stars with M = MTOV. Finally, we construct an analytic expression that accurately describes the radial dependence of the sound speed as a function of the neutron-star mass, thus providing an estimate of the maximum sound speed expected in a neutron star.

Item Type: Article
Subjects: Science Global Plos > Physics and Astronomy
Depositing User: Unnamed user with email support@science.globalplos.com
Date Deposited: 24 Apr 2023 07:14
Last Modified: 02 Feb 2024 04:28
URI: http://ebooks.manu2sent.com/id/eprint/628

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