Constraints on maximum neutron star mass from proto-neutron star evolution

TL;DR

This paper uses a Bayesian constrained relativistic model to study how the presence of hyperons affects the maximum mass of neutron stars, providing insights into their composition and stability.

Contribution

It introduces a Bayesian inference approach to constrain the finite-temperature equation of state for neutron stars, highlighting the impact of hyperons on maximum mass limits.

Findings

Maximum neutron star mass with hyperons is around 2.15 solar masses.

Observation of neutron stars above 2.2 solar masses suggests absence of hyperons.

Hyperonic proto-neutron stars can become metastable and collapse into black holes.

Abstract

A proto-neutron star (PNS) gets formed after a successful supernova when the stellar remnant decouples from the ejecta. In this study, we explore a relativistic framework for the finite-temperature $\beta$-equilibrium limit of equation of state (EOS), constrained via a Bayesian inference methodology. The EOS is constrained by minimal approximations on a few nuclear saturation properties, low-density pure neutron matter constraints from chiral effective field theory, and a neutron star (NS) maximum mass greater than 2.0 $M_{\odot}$. Two sets of EOS derived from the relativistic mean field model for nucleonic and hyperonic matter constrained by a Bayesian inference calculation at the zero temperature limit are used. The thermal adiabatic index ($\Gamma_{\rm Th}$) is calculated as a function of the baryonic density across several temperatures for both the sets. Our results suggest that the maximum NS mass is of the order of 2.15 $M_\odot$ if hyperons are present. In addition, the present study suggests that an observation of NS with mass larger than $2.2\ M_{\odot}$ can indirectly indicates the absence of hyperons in its core. The deleptonization of hyperonic PNS reduces the stellar maximum mass rendering the PNS exceeding the zero temperature maximum stellar (baryonic) mass limit becomes metastable which is prone to collapse into a black hole while PNS below such a mass threshold evolves to a stable NS.