# Full Transport Model of GW170817-Like Disk Produces a Blue Kilonova

## TL;DR

This paper presents the first 3D general relativistic neutrino transport simulations of a neutron star merger's accretion disk, demonstrating how neutrino interactions increase electron fraction and produce a blue kilonova.

## Contribution

It introduces a comprehensive 3D GRRMHD simulation of GW170817-like mergers, revealing the impact of neutrino transport on ejecta composition and kilonova color.

## Key findings

- Neutrino transport couples the disk's electron fraction globally.
- Electron fraction reaches up to Y_e ~ 0.4 in polar outflows.
- Nucleosynthesis predicts a blue kilonova from the disk wind.

## Abstract

The 2017 detection of the inspiral and merger of two neutron stars in gravitational waves and gamma rays was accompanied by a quickly-reddening transient. Such a transient was predicted to occur following a rapid neutron capture (r-process) nucleosynthesis event, which synthesizes neutron-rich, radioactive nuclei and can take place in both dynamical ejecta and in the wind driven off the accretion torus formed after a neutron star merger. We present the first three-dimensional general relativistic, full transport neutrino radiation magnetohydrodynamics (GRRMHD) simulations of the black hole-accretion disk-wind system produced by the GW170817 merger. We show that the small but non-negligible optical depths lead to neutrino transport globally coupling the disk electron fraction, which we capture by solving the transport equation with a Monte Carlo method. The resulting absorption drives up the electron fraction in a structured, continuous outflow, with electron fraction as high as $Y_e\sim 0.4$ in the extreme polar region. We show via nuclear reaction network and radiative transfer calculations that nucleosynthesis in the disk wind will produce a blue kilonova.