The Shapiro Conjecture: Prompt or Delayed Collapse in the head-on collision of neutron stars?

TL;DR

This paper investigates whether neutron star collisions lead to immediate black hole formation or delayed collapse, challenging previous conjectures by analyzing complex relativistic simulations.

Contribution

The study provides the first detailed relativistic simulation evidence that prompt black hole formation can occur in neutron star collisions, countering Shapiro's conjecture.

Findings

Prompt collapse is possible in neutron star collisions.

Shapiro's conjecture has limitations based on multiple time scales.

Relativistic simulations support immediate black hole formation.

Abstract

We study the question of prompt vs. delayed collapse in the head-on collision of two neutron stars. We show that the prompt formation of a black hole is possible, contrary to a conjecture of Shapiro which claims that collapse is delayed until after neutrino cooling. We discuss the insight provided by Shapiro's conjecture and its limitation. An understanding of the limitation of the conjecture is provided in terms of the many time scales involved in the problem. General relativistic simulations in the Einstein theory with the full set of Einstein equations coupled to the general relativistic hydrodynamic equations are carried out in our study.