Axisymmetric models for neutron star merger remnants with realistic thermal and rotational profiles

Giovanni Camelio,Tim Dietrich,Stephan Rosswog,Brynmor Haskell

doi:10.1103/physrevd.103.063014

Abstract

Merging neutron stars are expected to produce hot, metastable remnants in rapid differential rotation, which subsequently cool and evolve into rigidly rotating neutron stars or collapse to black holes. Studying this metastable phase and its further evolution is essential for the prediction and interpretation of the electromagnetic, neutrino, and gravitational signals from such a merger. In this work, we model binary neutron star merger remnants and propose new rotation and thermal laws that describe post-merger remnants. Our framework is capable to reproduce quasi-equilibrium configurations for generic equations of state, rotation and temperature profiles, including nonbarotropic ones. We demonstrate that our results are in agreement with numerical relativity simulations concerning bulk remnant properties like the mass, angular momentum, and the formation of a massive accretion disk. Because of the low computational cost for our axisymmetric code compared to full 3+1-dimensional simulations, we can perform an extensive exploration of the binary neutron star remnant parameter space studying several hundred thousand configurations for different equation of states.

Highlights

With densities substantially exceeding those in atomic nuclei, neutron stars (NSs) provide an interesting “astrophysical laboratory” to probe matter under the most extreme conditions and they can deliver physical information that complements other ongoing efforts to understand nuclear matter [1,2]
We consider a subset of equations of state (EOSs) from Read et al [36] that fulfill the most recent radius and maximum mass constraints obtained from nuclear physics and astrophysical observations [39]: ALF2 [40], SLy [41], APR4 [42], and ENG [43], see Appendix A 1
In this paper we studied realistic stationary models for postmerger configurations after a binary neutron star (BNS) merger

Summary

INTRODUCTION

With densities substantially exceeding those in atomic nuclei, neutron stars (NSs) provide an interesting “astrophysical laboratory” to probe matter under the most extreme conditions and they can deliver physical information that complements other ongoing efforts to understand nuclear matter [1,2]. NSs originate in supernova explosions or binary neutron star (BNS) mergers [3] In either case, they are hot and differentially rotating in the first minute of their lives [4,5]. Camelio et al [26] developed a technique to obtain a stationary, hot, differentially rotating, baroclinic NS model, opening the way to a larger class of thermal and rotational profiles. Modeling BNS merger remnants with stationary codes is an important complementary approach to full hydrodynamical simulations, since it allows for a much faster and wider exploration of the possible parameter space. We first develop a model for the stationary remnant of a BNS system at ∼10–50 ms after merger, which is differentially rotating, hot, and baroclinic (Sec. II).

Equation of state

Euler equation

Stellar properties

Selected models

CONCLUSION

Neutron star