Spinning Down Neutron-star Merger Remnants with the Tayler–Spruit Dynamo: Global Simulations Reveal the Formation of Massive Disks and Neutron-rich Ejecta
- 1California Institute of Technology
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 unmodeled Tayler–Spruit dynamo action can qualitatively alter the rotational evolution, collapse prospects, disk formation, and multimessenger signatures of long-lived neutron-star merger remnants.
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BibTeX
@article{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},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = oct,
doi = {10.3847/2041-8213/aeac1b},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeac1b},
note = {CC BY 4.0},
}
RIS
TY - JOUR
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 - 2026/10/16
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeac1b
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeac1b
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 unmodeled Tayler–Spruit dynamo action can qualitatively alter the rotational evolution, collapse prospects, disk formation, and multimessenger signatures of long-lived neutron-star merger remnants.
SN - 2041-8205
SN - 2041-8213
ER -