Universality and properties of neutron star type I critical collapses

TL;DR

This paper investigates the critical solutions in neutron star mergers, demonstrating their role as semi-attractors in the solution space of Einstein's equations and exploring their properties and basins of attraction.

Contribution

It identifies and characterizes neutron star critical solutions as semi-attractors, analyzing their dependence on conserved quantities and constructing initial data phase spaces.

Findings

Neutron star critical solutions act as semi-attractors.

The attraction basin of these solutions is mapped and characterized.

Critical indices depend on conserved quantities and classify semi-attractors.

Abstract

We study the neutron star axisymmetric critical solution previously found in the numerical studies of neutron star mergers. Using neutron star-like initial data and performing similar merger simulations, we demonstrate that the solution is indeed a semi-attractor on the threshold plane separating the basin of a neutron star and the basin of a black hole in the solution space of the Einstein equations. In order to explore the extent of the attraction basin of the neutron star semiattractor, we construct initial data phase spaces for these neutron star-like initial data. From these phase spaces, we also observe several interesting dynamical scenarios where the merged object is supported from prompt collapse. The properties of the critical index of the solution, in particular, its dependence on conserved quantities, are then studied. From the study, it is found that a family of neutron star semi-attractors exist that can be classified by both their rest masses and ADM masses.