Handing off the outcome of binary neutron star mergers for accurate and long-term post-merger simulations

Abstract

We perform binary neutron star (BNS) merger simulations in full dynamical general relativity with IllinoisGRMHD, on a Cartesian grid with adaptive-mesh refinement. After the remnant black hole (BH) has become nearly stationary, the evolution of the surrounding accretion disk on Cartesian grids over long timescales (∼1s) is suboptimal, as the plasma flows obliquely across coordinate lines and numerical errors quickly dissipate angular momentum from the disk. To address this, we present the HandOff, a set of computational tools that enables the transfer of general relativistic magnetohydrodynamic (GRMHD) and spacetime data from IllinoisGRMHD to Harm3d, a GRMHD code that specializes in modeling BH accretion disks in static spacetimes over long timescales, making use of general coordinate systems with spherical topology. We demonstrate that the HandOff allows for a smooth and reliable transition of GRMHD fields and spacetime data, enabling us to efficiently and reliably evolve BNS dynamics well beyond merger. We also discuss future plans, which involve incorporating advanced equations of state and neutrino physics into BNS simulations using the HandOff approach.

Addition of tabulated equation of state and neutrino leakage support to illinoisgrmhd

“…Because of this, we have taken special care to ensure that all of the new features in IllinoisGRMHD are consistent with those in HARM3D+NUC [6]. The simulation data will be transferred from IllinoisGRMHD to HARM3D+NUC (a code specially designed to accurately and reliably model BH accretion disks) using our recently developed HandOff code [81], and the simulation will continue for O (∼seconds). Results of these simulations will be presented in a future paper.…”

“…For well over a decade, both OrigGRMHD and IllinoisGRMHD have been used to model a plethora of astrophysical scenarios, including magnetized binary neutron stars (BNS) [58,[76][77][78][79][80][81], binary BH-NS [82][83][84][85][86][87][88], BH accretion disks [89][90][91][92][93][94][95], binary white dwarf-NS [96,97], rotating NSs [98,99], gravitational collapse of supermassive stars [100], magnetized Bondi accretion [101], and magnetized hypermassive neutron stars (HMNS) [102][103][104][105][106][107][108], to name a few. We also highlight Frankfurt/IllinoisGRMHD [25], whose feature set exceeds that of the original IllinoisGRMHD, but like OrigGRMHD is currently a closed-source code.…”

Advancing Computational Methods to Understand the Dynamics of Ejection, Accretion, Winds, and Jets in Binary Neutron Star Mergers

“…Below we describe briefly the steps required for this process. For a detailed description of the codes involved, see Lopez Armengol, et al (2021).…”

HARM3D+NUC: GRMHD, nuclear tables and neutrino leakage

“…This will be done with two GRMHD codes with dynamical metrics: IllinoisGRMHD and Spritz (Etienne et al 2015;Cipolletta et al 2020). Then we will interpolate the primitives and numerical grid into HARM3D using the methods developed in Lopez Armengol et al (2021), where we will evolve the post-merger evolution. Finally, we will use Skynet (Lippuner & Roberts 2017) to evaluate the final abundances of heavy elements created, and study the outflow.…”