2025/01/22 by Izquierdo, Manuel R., Palenzuela, Carlos, Liebling, Steven +2
#FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2501.13154
We perform numerical relativity simulations of black hole-neutron star (BH-NS) mergers with a fixed mass ratio of q = 3, varying the BH spin to produce a wide range of post-merger accretion disk masses. Our high-order numerical scheme, fine resolution, and Large Eddy Simulation techniques enable us to achieve likely the most resolved BH-NS merger simulations to date, capturing the post-merger magnetic field amplification driven by turbulent dynamo processes. Following tidal disruption and during disk formation, the Kelvin-Helmholtz instability in the spiral arm drives a turbulent state in which the magnetic field, initialized to a realistic average value of 1011 \rmG, grows to an average of approximately 1014 \rmG in the first ≈ 20 ms post-merger. Notably, the dimensionless magnetic flux on the BH, ϕ, evolves similarly across nearly two orders of magnitude in disk mass. This similarity, along with estimates from longer numerical simulations of the decay of the mass accretion rate, suggests a universal timescale at which the dimensionless flux saturates at a magnetically arrested state (MAD) such that ϕ≈ 50 at t\rm MAD \gtrsim 10 \rm s. The unified framework of Gottlieb et al. (2023) established that the MAD timescale sets the duration of the resulting compact binary gamma-ray burst (cbGRB), implying that all BH-NS mergers contribute to the recently detected new class of long-duration cbGRBs.