RELATIVISTIC SIMULATIONS OF BLACK HOLE–NEUTRON STAR COALESCENCE: THE JET EMERGES
We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of a binary black hole–neutron star (BHNS) on a quasicircular orbit that undergoes merger. The binary mass ratio is 3:1, the black hole initial spin parameter a / m = 0.75 ?> (m is the black hole Christodoulou mass) aligned with the orbital angular momentum, and the neutron star is an irrotational Γ = 2 ?> polytrope. About two orbits prior to merger (at time t = t B ?> ), we seed the neutron star with a dynamically weak interior dipole magnetic field that extends into the stellar exterior. At t = t B ?> , the exterior has a low-density atmosphere with a constant plasma parameter β ≡ P gas / P mag ?> . Varying β at tB in the exterior from 0.1 to 0.01, we find that at a time ∼ 4000 M ∼ 100 ( M NS / 1.4 M ⊙ ) ms ?> (M is the total (ADM) mass) following the onset of accretion of tidally disrupted debris, magnetic winding above the remnant black hole poles builds up the magnetic field sufficiently to launch a mildly relativistic, collimated outflow—an incipient jet. The duration of the accretion and the lifetime of the jet is Δ t ∼ 0.5 ( M NS / 1.4 M ⊙ ) ?> s. Our simulations furnish the first explicit examples in GRMHD that show that a jet can emerge following a BHNS merger.