Current Status of Numerical-Relativity Simulations in Kyoto

TL;DR

This paper reports on advanced numerical relativity simulations of stellar core collapse and binary neutron star mergers, highlighting the effects of rotation, EOS composition, and resulting gravitational wave and neutrino emissions.

Contribution

It presents new simulation results incorporating finite-temperature EOS, neutrino cooling, and hyperons, revealing the dependence of collapse outcomes on initial rotation and EOS type.

Findings

Rapid rotation leads to torus-shaped shock deformation.

Long-lived HMNS forms for certain masses with nucleonic EOS.

Neutrino luminosity and gravitational wave amplitudes are quantified.

Abstract

We describe the current status of our numerical simulations for the collapse of a massive stellar core to a BH and the BNS mergers, performed in the framework of full general relativity incorporating finite-temperature EOS and neutrino cooling. For the stellar core collapse simulation, we present the latest numerical results. We employed a purely nucleonic EOS (Shen-EOS). As an initial condition, we adopted a 100 $M_{\odot}$ presupernova model calculated by Umeda and Nomoto. Changing the degree of rotation for the initial condition, we clarify the strong dependence of the outcome of the collapse on this. When the rotation is rapid enough, the shock wave formed at the core bounce is deformed to be a torus-like shape. Then, the infalling matter is accumulated in the central region due to the oblique shock at the torus surface, hitting the PNS and dissipating the kinetic energy there. As a result, outflows can be launched. The PNS eventually collapses to a BH and an accretion torus is formed around it. We also found that the evolution of the BH and torus depends strongly on the rotation initially given. In the BNS merger simulations, we in addition employ an EOS incorporating a degree of freedom for hyperons. The numerical simulations show that for the purely nucleonic EOS, a HMNS with a long lifetime ($\gg 10$ ms) is the outcome for the total mass $M \lesssim 3.0M_{\odot}$. By contrast, the formed HMNS collapses to a BH in a shorter time scale with the hyperonic EOS for $M \gtrsim 2.7M_{\odot}$. It is shown that the typical total neutrino luminosity of the HMNS is $\sim 3$--$10\times 10^{53}$ ergs/s and the effective amplitude of gravitational waves from the HMNS is 2--$6 \times 10^{-22}$ at $f\approx 2$--2.5 kHz for a source distance of 100 Mpc.