Simulations of stellar collapses to black holes: Influence of hyperons

Abstract

Stellar core collapse to a black hole is an event where extremely high temperatures and densities are reached. It is then expected that additional particles to nucleons and electrons appear, as hyperons. We present numerical simulations of the collapse of massive stars to black holes, with an equation of state based on the Lattimer-Swesty one, but allowing for the presence of Λ hyperons. A feature of these equations of state is that its cold and beta-equilibrium version allows for neutrons stars with almost two solar masses, marginally compatible with recent observations. Spherically symmetric simulations, under some conditions, may show the effect of a phase transition to hyperonic matter before the appearance of the black hole. We show axisymmetric simulations, too, where this phase transition would be smoothed, but where gravitational waves show clear imprint of the presence of hyperons.