Efficient magnetic-field amplification due to the Kelvin-Helmholtz instability in binary neutron star mergers

We explore magnetic-field amplification due to the Kelvin-Helmholtz instability during binary neutron star mergers. By performing high-resolution general relativistic magnetohydrodynamics simulations with a resolution of 17.5 m for 4--5 ms after the onset of the merger on the Japanese supercomputer ``K'', we find that an initial magnetic field of moderate maximum strength 10¹³ G is amplified at least by a factor of ≈10³. We also explore the saturation of the magnetic-field energy and our result shows that it is likely to be 4×10⁵⁰ erg, which is 0.1% of the bulk kinetic energy of the merging binary neutron stars.