Abstract
We propose a universal approximation of the equation of state of superdense matter in neutron star (NS) interiors. It contains only two parameters, the pressure and the density at the center of the maximally massive neutron star. We demonstrate the validity of this approximation for a wide range of different types of equations of state, including both baryonic and hybrid models. Combined with recently discovered correlations of internal (density, pressure, and speed of sound at the center) and external (mass, radius) properties of a maximally massive neutron star, this approximation turns out to be an effective tool for determining the equation of state of superdense matter using astrophysical observations.
Notes
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\(\gamma_{\text{max}}^{\text{(fit)}}\) may differ significantly from the actual value of the adiabatic index at the point \(\rho=\rho_{\text{TOV}}\). Although the fitting error (1c) for \(c_{\text{s}_{\text{TOV}}}\) is generally not too large, the error of \(c_{\text{s}_{\text{TOV}}}^{2}\) in a few worst cases exceeds \(50\%\).
Stronger limits can be obtained from other observations.
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The work was supported by RSF grant no. 19-12-00133 (PS) and by an Advanced ERC grant MultiJets (DO, TP).
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Ofengeim, D.D., Shternin, P.S. & Piran, T. Maximal Mass Neutron Star as a Key to Superdense Matter Physics. Astron. Lett. 49, 567–574 (2023). https://doi.org/10.1134/S1063773723100055
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DOI: https://doi.org/10.1134/S1063773723100055