Implications of supermassive neutron stars for the form of the equation of state of hybrid stars

TL;DR

This paper explores how supermassive neutron star observations constrain the equation of state of hybrid stars, using the CSS parametrization, and finds specific conditions under which such stars can exist.

Contribution

It introduces constraints on the EOS parameters for supermassive hybrid stars using CSS parametrization and analyzes their implications for maximum mass and tidal deformability.

Findings

Lower transition energy density favors supermassive hybrid stars.

Energy density discontinuity above 180 MeV/fm^3 limits maximum mass.

Supermassive neutron star observations exclude twin star configurations.

Abstract

The observations of PSR J0952-0607 and the second object in GW190814 event indicate the possible existence of supermassive neutron stars. In this work, by using the Constant-Sound-Speed (CSS) parametrization to describe the equation of state (EOS) of quark matter, the constraints on the EOS parameters from supermassive hybrid stars are investigated through the Maxwell and Gibbs constructions. It is shown that to support a supermassive hybrid star, a lower transition energy density, a smaller energy density discontinuity and a higher sound speed of quark matter are favored. For the constructed hybrid star EOS model, the maximum mass of the corresponding hybrid stars will not meet the lower mass limit of the second object in GW190814 if the energy density discontinuity takes a value higher than $180~{\rm MeV~fm^{-3}}$. Moreover, it is confirmed that the supermassive neutron star observation can also rule out the existence of twin stars as a supermassive hybrid star requires a relatively small energy density discontinuity. Finally, we give a rough estimate of the lower limit of the dimensionless tidal deformability of neutron stars which ranges from 2 to 3.