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 postmerger accretion disk masses. Our high-order numerical scheme, fine resolution, and large eddy simulation techniques enable us to achieve likely one of the most resolved BH-NS merger simulations to date, capturing the postmerger 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 ${10}^{11}\mathrm{G}$, grows to an average of approximately ${10}^{14}\mathrm{G}$ in the first $\approx 20\mathrm{ms}$ postmerger. Notably, the dimensionless magnetic flux on the BH, $\varphi$, evolves similarly across nearly 2 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 least for this equation of state) at which the dimensionless flux saturates at a magnetically arrested state (MAD) such that $\varphi \approx 50$ at $t_{\mathrm{MAD}}\gtrsim 10\mathrm{s}$. The unified framework of Gottlieb et al. [Astrophys. J. Lett. 958, L33 (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.

Close

PrevNext

View figure in article

• Gamma ray bursts
• General relativity equations & solutions
• Astronomical black holes
• Neutron stars & pulsars
• Astrophysical electromagnetic fields
• Astrophysical & cosmological simulations
• Numerical relativity
• Numerical simulations in gravitation & astrophysics