Energy Extraction from Spinning Black Holes via Relativistic Jets
  It has for long been an article of faith among astrophysicists that black
hole spin energy is responsible for powering the relativistic jets seen in
accreting black holes. Two recent advances have strengthened the case. First,
numerical general relativistic magnetohydrodynamic simulations of accreting
spinning black holes show that relativistic jets form spontaneously. In at
least some cases, there is unambiguous evidence that much of the jet energy
comes from the black hole, not the disk. Second, spin parameters of a number of
accreting stellar-mass black holes have been measured. For ballistic jets from
these systems, it is found that the radio luminosity of the jet correlates with
the spin of the black hole. This suggests a causal relationship between black
hole spin and jet power, presumably due to a generalized Penrose process.
