Relativistic simulations of black hole-neutron star coalescence: The jet emerges

Vasileios Paschalidis, Milton Ruiz, Stuart L. Shapiro

Research output: Contribution to journalArticlepeer-review


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 = tB), we seed the neutron star with a dynamically weak interior dipole magnetic field that extends into the stellar exterior. At t=tB, the exterior has a low-density atmosphere with a constant plasma parameter β ≡ Pgas/Pmag. Varying β at tB in the exterior from 0.1 to 0.01, we find that at a time ∼4000M ∼ 100(MNS/1.4M)(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 δt ∼ 0.5(MNS/1.4M)s. Our simulations furnish the first explicit examples in GRMHD that show that a jet can emerge following a BHNS merger.

Original languageEnglish (US)
Article numberL14
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Jun 10 2015


  • black hole physics
  • gamma-ray burst: general
  • gravitation
  • gravitational waves
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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