Assessing the impact of uniform rotation on the structure of neutron stars

TL;DR

This paper investigates how uniform rotation influences the maximum mass and radii of neutron stars, providing insights into the stiffness of the equation of state at high densities and implications for massive neutron stars.

Contribution

It introduces a detailed analysis of the effects of uniform rotation on neutron star structure, connecting observational data with theoretical models to constrain the EOS.

Findings

Rotation increases the maximum mass of neutron stars.

Rotation affects the radii of neutron stars at high densities.

Implications for the existence of very massive neutron stars.

Abstract

Driven by recent laboratory experiments and astronomical observations, significant advances have deepened our understanding of neutron-star physics. NICER's Pulse Profile Modeling has refined our knowledge of neutron star masses and radii, while gravitational-wave detections have revealed key insights into the structure of neutron stars. Particularly relevant is the extraction of the tidal deformability by the LIGO-Virgo collaboration and the most recent determination of stellar radii by NICER, both suggesting a relatively soft equation of state (EOS) at intermediate densities. Additionally, measurements from the PREX collaboration and from pulsar timing suggest instead that the EOS is stiff in the vicinity of saturation density and at the highest densities accessible to date. But how stiff can the EOS be at these very high densities? Recent events featuring compact objects near the "lower mass gap" have raised questions about the existence of very massive neutron stars. Motivated by this finding and in light of new refinements to theoretical models, we explore the possibility that these massive objects may indeed be rapidly rotating neutron stars. We explore how rotation affects both the maximum neutron star mass and their associated radii, and discuss the implications they may have on the equation of state.