Spinning down neutron-star merger remnants with the Tayler-Spruit dynamo: Global simulations reveal the formation of massive disks and neutron-rich ejecta
Abstract
Magnetic-field amplification and angular momentum (AM) transport critically shape the secular evolution, lifetime, and electromagnetic signatures of binary neutron-star merger remnants. While the magnetorotational instability can operate in the outer negative-shear regions of the neutron-star remnant and accretion disk, the positive-shear, stably stratified core may instead be susceptible to the Tayler-Spruit dynamo. We present the first global, long-term general-relativistic neutrino-radiation magnetohydrodynamics simulations of a neutron-star merger remnant incorporating the unresolved Tayler-Spruit dynamo through a new mean-field dynamo subgrid prescription. Our axisymmetric simulations starting from a realistic merger remnant show that the Tayler-Spruit dynamo is primarily active in high-latitude regions of the remnant core. The resulting Maxwell stresses redistribute AM on a spin-down timescale of a few hundred milliseconds, substantially flattening the core rotation profile and transferring mass and AM from the outer remnant into the disk. This produces a more massive, extended, and strongly magnetized disk with a low electron fraction, leading to substantially more neutron-rich ejecta. Our results demonstrate that currently unmodelled Tayler-Spruit dynamo action can qualitatively alter the rotational evolution, collapse prospects, disk formation, and multi-messenger signatures of long-lived neutron-star merger remnants.
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BibTeX
@misc{ng2026spinning,
title = {{Spinning down neutron-star merger remnants with the Tayler-Spruit dynamo: Global simulations reveal the formation of massive disks and neutron-rich ejecta}},
author = {Harry Ho-Yin Ng and Elias R. Most},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.28556},
eprint = {2607.28556},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.28556},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Spinning down neutron-star merger remnants with the Tayler-Spruit dynamo: Global simulations reveal the formation of massive disks and neutron-rich ejecta
AU - Harry Ho-Yin Ng
AU - Elias R. Most
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2607.28556
UR - https://arxiv.org/abs/2607.28556
AB - Magnetic-field amplification and angular momentum (AM) transport critically shape the secular evolution, lifetime, and electromagnetic signatures of binary neutron-star merger remnants. While the magnetorotational instability can operate in the outer negative-shear regions of the neutron-star remnant and accretion disk, the positive-shear, stably stratified core may instead be susceptible to the Tayler-Spruit dynamo. We present the first global, long-term general-relativistic neutrino-radiation magnetohydrodynamics simulations of a neutron-star merger remnant incorporating the unresolved Tayler-Spruit dynamo through a new mean-field dynamo subgrid prescription. Our axisymmetric simulations starting from a realistic merger remnant show that the Tayler-Spruit dynamo is primarily active in high-latitude regions of the remnant core. The resulting Maxwell stresses redistribute AM on a spin-down timescale of a few hundred milliseconds, substantially flattening the core rotation profile and transferring mass and AM from the outer remnant into the disk. This produces a more massive, extended, and strongly magnetized disk with a low electron fraction, leading to substantially more neutron-rich ejecta. Our results demonstrate that currently unmodelled Tayler-Spruit dynamo action can qualitatively alter the rotational evolution, collapse prospects, disk formation, and multi-messenger signatures of long-lived neutron-star merger remnants.
ER -