Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations

TL;DR

This paper investigates the early rotational evolution of proto-neutron stars, analyzing how their mass, spin, and I-Love-Q relations change during cooling and contraction phases using finite temperature equations of state.

Contribution

It models the spin evolution of proto-neutron stars with finite temperature effects and demonstrates the violation and subsequent restoration of I-Love-Q relations during early life.

Findings

Neutron stars do not reach maximum mass and rotation rates at the end of proto-neutron star phase.

Rapid rotation at birth does not persist into the mature neutron star stage.

I-Love-Q relations are violated in the first second but hold afterward.

Abstract

Shortly after its birth in a gravitational collapse, a proto-neutron star enters in a phase of quasi-stationary evolution characterized by large gradients of the thermodynamical variables and intense neutrino emission. In few tens of seconds the gradients smooth out while the star contracts and cools down, until it becomes a neutron star. In this paper we study this phase of the proto-neutron star life including rotation, and employing finite temperature equations of state. We model the evolution of the rotation rate, and determine the relevant quantities characterizing the star. Our results show that an isolated neutron star cannot reach, at the end of the evolution, the maximum values of mass and rotation rate allowed by the zero-temperature equation of state. Moreover, a mature neutron star evolved in isolation cannot rotate too rapidly, even if it is born from a proto-neutron star rotating at the mass-shedding limit. We also show that the I-Love-Q relations are violated in the first second of life, but they are satisfied as soon as the entropy gradients smooth out.