Shapiro conjecture: Prompt or delayed collapse in the head-on collision ofneutron stars? art. no. 121501

We study the question of prompt versus delayed collapse in the head-on coll ision of two neutron stars. We show that the prompt formation of a black ho le is possible, contrary to a conjecture of Shapiro which claims that colla pse is delayed until after neutrino cooling. An understanding of the limita tion of the conjecture is provided in terms of the many time scales involve d in the problem. General relativistic simulations with the full set of Ein stein equations coupled to the general relativistic hydrodynamic equations are carried out.