Supermassive Neutron Stars Rule Out Twin Stars

TL;DR

This paper explores the relationship between neutron star maximum mass and phase transitions to quark matter, concluding that twin stars cannot coexist with neutron stars exceeding 2.2 solar masses.

Contribution

It demonstrates that high-mass neutron stars and the existence of twin stars are mutually exclusive due to the energy density discontinuity in the EoS.

Findings

High maximum masses require small energy density discontinuities.

Twin stars are incompatible with neutron stars having masses above 2.2 solar masses.

Soft equations of state cannot produce visible twin stars with high masses.

Abstract

We investigate the implications of a hypothetical $2.5\,\mathrm{M_\odot}$ neutron star in regard to the possibility of a strong phase transition to quark matter. We use equations of state (EoS) of varying stiffness provided by a parameterizable relativistic mean filed model transitioning in a first order phase transition to quark matter with a constant speed of sound. We find a strong connection between the discontinuity in energy density and the maximal mass generated by the EoS. We demonstrate, that high maximal masses cannot be realized for large discontinuities in energy density, which are necessary for visible twin stars, especially for soft EoSs. As a result twin stars and maximal masses of $M_{max}\gtrsim2.2\,M_\odot$ are mutually exclusive.