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Abstract

Short Gamma-Ray Bursts (SGRB) are among the most energetic explosions in the universe, releasing in less than a second the energy emitted by the whole Galaxy over one year. Despite decades of observations, the nature of their “central engine”, where the physical conditions are the most extreme, remains largely obscure. Here we show that, starting from generic initial conditions consisting of a binary system of magnetized neutron stars in full general relativity, the final fate of the system is a rapidly spinning black hole (BH) surrounded by a hot and highly magnetized torus feeding a jet with half opening-angle of ∼30 deg. In particular, performing simulations on timescales four times longer than previous ones, we show that magnetohydrodynamical instabilities developing after BH formation amplify an initial turbulent magnetic field of ∼1012 G, to produce an ordered jet along the BH spin axis with strengths ∼1015 G. The formation of this configuration from abinitio calculations provides strong evidence that the merger of neutron-star (NS) binaries is potentially behind the central engine of a SGRB. We anticipate that our study will set the basis for the realistic description of the physics behind one the most extreme phenomena in the universe.