Gravitational waves, neutrino emissions, and effects of hyperons in binary neutron star mergers

Abstract

Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that for the nucleonic and hyperonic EOS, a hyper massive neutron star (HMNS) with a long lifetime $(t_{\rm life}\gtrsim 10 {\rm ms})$ is the outcome for the total mass $\approx 2.7 M_\odot$. For the total mass $\approx 3 M_\odot$, a long-lived (short-lived with $t_{\rm life}\approx 3 {\rm ms}$) HMNS is the outcome for the nucleonic (hyperonic) EOS. It is shown that the typical total neutrino luminosity of the HMNS is $\sim 3$ -- $6 \times 10^{53} {\rm erg /s}$ and the effective amplitude of gravitational waves from the HMNS is 1 -- $4\times 10^{-22}$ at $f\approx 2$ -- $3.2 {\rm kHz}$ for a source of distance of 100 Mpc. During the HMNS phase, characteristic frequencies of gravitational waves shift to a higher frequency for the hyperonic EOS in contrast to the nucleonic EOS in which they remain constant approximately. Our finding suggests that the effects of hyperons are well imprinted in gravitational wave and its detection will give us a potential opportunity to explore the composition of the neutron star matter. We present the neutrino luminosity curve when a black hole is formed as well.