Collision of 1.4 $M_{\odot}$ Neutron Stars: Dynamical or Quasi-Equilibrium?

TL;DR

This paper challenges Shapiro's conjecture that neutron star collisions do not form black holes before neutrino cooling, demonstrating that such collisions are too dynamical for quasi-equilibrium assumptions, based on numerical simulations of 1.4 solar mass neutron stars.

Contribution

The paper provides a counterexample to Shapiro's conjecture using numerical simulations, showing that dynamical effects dominate over quasi-equilibrium assumptions in certain neutron star collisions.

Findings

Neutron star collisions can be highly dynamical, invalidating quasi-equilibrium analysis.

Numerical simulations of 1.4 solar mass neutron stars show collapse to black holes is possible.

Shapiro's argument about simulation accuracy does not negate the dynamical nature of these collisions.

Abstract

Shapiro put forth a conjecture stating that neutron stars in head-on collisions (infalling from infinity) will not collapse to black holes before neutrino cooling, independent of the mass of the neutron stars. In a previous paper we carried out a numerical simulation showing a counter example based on 1.4 $M_{\odot}$ neutron stars, and provided an analysis explaining why Shapiro's argument was not applicable for this case. A recent paper by Shapiro put forth an argument suggesting that numerical simulations of the 1.4 $M_{\odot}$ collisions could not disprove the conjecture with the accuracy that is presently attainable. We show in this paper that this argument is not applicable for the same reason that the Shapiro conjecture is not applicable to the 1.4 $M_{\odot}$ neutron star collision, namely, the collision is too dynamical to be treated by quasi-equilibrium arguments.