Consequences of a strong phase transition in the dense matter equation of state for the rotational evolution of neutron stars

TL;DR

This paper investigates how a strong phase transition in dense matter affects neutron star stability, leading to distinct configurations and potential observable phenomena like spin frequency limits and energy releases.

Contribution

It demonstrates the existence of two disjoint neutron star families caused by a phase transition and explores their astrophysical implications within general relativity.

Findings

Identification of high-mass twin neutron star configurations.

Explanation of the observed spin frequency cutoff.

Potential for energy release during mini-collapse events.

Abstract

We explore the implications of a strong first-order phase transition region in the dense matter equation of state in the interiors of rotating neutron stars, and the resulting creation of two disjoint families of neutron-star configurations (the so-called high-mass twins). We numerically obtained rotating, axisymmetric, and stationary stellar configurations in the framework of general relativity, and studied their global parameters and stability. The instability induced by the equation of state divides stable neutron star configurations into two disjoint families: neutron stars (second family) and hybrid stars (third family), with an overlapping region in mass, the high-mass twin-star region. These two regions are divided by an instability strip. Its existence has interesting astrophysical consequences for rotating neutron stars. We note that it provides a natural explanation for the rotational frequency cutoff in the observed distribution of neutron star spins, and for the apparent lack of back-bending in pulsar timing. It also straightforwardly enables a substantial energy release in a mini-collapse to another neutron-star configuration (core quake), or to a black hole.