A Tale of Two Jets
  One of the most interesting high-energy, astrophysical phenomena are
relativistic jets emitted from highly localized sky location. Such jets are
common in Nature, observed to high redshift and in a range of wavelengths.
Their precise generation mechanism remains a bit of a mystery, but they are
generically believed to be powered by black holes. We here summarize the recent
simulations of Palenzuela, Lehner and Liebling that shed light on the jet
generation mechanism. These authors studied the merger of two non-spinning
black holes in the presence of a magnetic field, perpendicular to the orbital
plane and anchored by a circumbinary accretion disk, in the "force-free"
approximation. They found that each black hole essentially acts as a "straw"
that stirs the magnetic field lines around the center of mass as the black
holes inspiral. The twisting of the magnetic field lines then generates jets
around each black hole, even though these are not spinning. Their simulations
show the formation of such a dual jet geometry and how it transitions to a
single jet one, as the black holes merge due to gravitational wave emission.
