Mass ejection from disks surrounding a low-mass black hole: Viscous neutrino-radiation hydrodynamics simulation in full general relativity

Abstract

New viscous neutrino-radiation hydrodynamics simulations are performed for accretion disks surrounding a spinning black hole with low mass 3M and dimensionless spin 0.8 or 0.6 in full general relativity, aiming at modeling the evolution of a merger remnant of massive binary neutron stars or low-mass black hole-neutron star binaries. We reconfirm the following results found by previous studies of other groups: 15-30% of the disk mass is ejected from the system with the average velocity of ∼ 5-10% of the speed of light for the plausible profile of the disk as merger remnants. In addition, we find that for the not extremely high viscous coefficient case, the neutron richness of the ejecta does not become very high, because weak interaction processes enhance the electron fraction during the viscous expansion of the disk before the onset of the mass ejection, resulting in the suppression of the lanthanide synthesis. For high-mass disks, the viscous expansion timescale is increased by a longer-term neutrino emission, and hence, the electron fraction of the ejecta becomes even higher. We also confirm that the mass distribution of the electron fraction depends strongly on the magnitude of the given viscous coefficient. This demonstrates that a first-principle magnetohydrodynamics simulation is necessary for black hole-disk systems with sufficient grid resolution and with sufficiently long timescale (longer than seconds) to clarify the nucleosynthesis and electromagnetic signals from them.

Binary Neutron Star Merger Simulations with a Calibrated Turbulence Model

“…They also affected the tidal tail, which was irradiated after colliding with the faster shock-accelerated outflows that were launched after the merger [58]. Turbulent angular momentum transport in the remnant accretion disk and neutrino heating are expected to power additional outflows on a timescale of a few seconds [44,47,56,57,61,62,[125][126][127][128][129][130][131]. These secular ejecta are expected to dominate the overall nucleosynthesis and electromagnetic signal from BNS mergers [58,132].…”

“…Multi-messenger observations of BNS mergers are starting to constrain the poorly-known properties of matter at extreme densities [11,12,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] and the physical processes powering short γ-ray bursts (SGRBs) [37][38][39][40][41][42]. They are also beginning to reveal the role played by compact binary mergers in the chemical enrichment of the galaxy with r-process elements [8,13,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62]. The key to the solution of some of the most pressing open problems in nuclear and high-energy astrophysics-such as the origin of heavy elements, the nature of neutron stars (NSs)...…”

“…The GRLES or viscous approaches are the only way to perform long-term simulations of the postmerger evolution for multiple systems [56,61,62]. However, the results from these simulations inevitably depend on the adopted subgrid model.…”

Comparison of momentum transport models for numerical relativity

“…Another complementary strategy is to model subgrid-scale transport effects by adding effective stress, heat and particle conduction, and dynamo terms to the large-scale evolution equations. Several such attempts have been made for relativistic hydrodynamics in the context of binary neutron star postmerger remnants [3][4][5][6][7] and black hole accretion (also often with postmerger applications) [8,9] and, of course, in Newtonian hydrodynamics turbulence modeling is a vast endeavor. (For book-length treatments, see [10,11].…”

“…In this paper, we shall mostly be concerned with mean-field models. The most famous is the alpha-viscosity prescription of Shakura and Sunyaev [24], and a number of the above-mentioned numerical relativity studies [3,5,6,9] follow the alpha-viscosity path of modeling unresolved turbulence as a viscosity via the Navier-Stokes equations. It should be remembered that momentum transport is only one of the large-scale effects of turbulence.…”