Tayler-Spruit dynamo in binary neutron star merger remnants

In binary neutron star mergers, the remnant can be stabilized by differential rotation before it collapses into a black hole.

Therefore, the angular momentum transport mechanisms are crucial for predicting the lifetime of the hypermassive neutron star.

One such mechanism is the Tayler-Spruit dynamo, and recent simulations have shown that it could grow in proto-neutron stars formed during supernova explosions.

We aim to investigate whether hypermassive neutron stars with high neutrino viscosity could be unstable to the Tayler-Spruit dynamo and study how magnetic fields would evolve in this context.

Using a one-zone model based on the result of a 3D GRMHD simulation, we investigate the time evolution of the magnetic fields generated by the Tayler-Spruit dynamo.

In addition, we analyze the dynamics of the 3D GRMHD simulation to determine whether the dynamo is present.

Our one-zone model predicts that the Tayler-Spruit dynamo can increase the toroidal magnetic field to $ \ge 10^{17}$ G and the dipole field to amplitudes $\ge 10^{16}$ G.

The dynamo's growth timescale depends on the initial large-scale magnetic field right after the merger.

In the case of a long-lived hypermassive neutron star, an initial magnetic field of $\ge 10^{12}$ G would be enough for the magnetic field to be amplified in a few seconds.

However, we show that the resolution of the current GRMHD simulations is insufficient to resolve the Tayler-Spruit dynamo due to high numerical dissipation at small scales.

We find that the Tayler-Spruit dynamo could occur in hypermassive neutron stars and shorten their lifetime, which would have consequences on multi-messenger observations.

;Comment: 13 pages, 9 figures, submitted to A&A