Hyperons in Neutron Stars

TL;DR

This paper reviews how hyperons affect neutron star properties, focusing on the softening of the equation of state, the maximum mass challenge, and implications for cooling and r-mode instability, considering recent high-mass pulsar observations.

Contribution

It provides a comprehensive review of hyperons' impact on neutron star equations of state and discusses potential solutions to the hyperon puzzle in light of recent pulsar mass measurements.

Findings

Hyperons cause softening of the neutron star equation of state.

Recent high-mass pulsar data challenge existing hyperon models.

Hyperons influence neutron star cooling and r-mode instability.

Abstract

In this work I briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve due the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 ($1.667\pm 0.021 M_\odot$), PSR J1614-2230 ($1.97 \pm 0.04 M_\odot$), and PSR J0348+0432 ($2.01 \pm 0.04 M_\odot$). Some of the solutions proposed to tackle this problem are discussed. Finally, I re-examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.