Extracting black-hole rotational energy: The generalized Penrose process
Abstract
In the case involving particles, the necessary and sufficient condition for the Penrose process to extract energy from a rotating black hole is absorption of particles with negative energies and angular momenta. No torque at the black-hole horizon occurs. In this article we consider the case of arbitrary fields or matter described by an unspecified, general energy-momentum tensor Tμν and show that the necessary and sufficient condition for extraction of a black hole's rotational energy is analogous to that in the mechanical Penrose process: absorption of negative energy and negative angular momentum. We also show that a necessary condition for the Penrose process to occur is for the Noether current (the conserved energy-momentum density vector) to be spacelike or past directed (timelike or null) on some part of the horizon. In the particle case, our general criterion for the occurrence of a Penrose process reproduces the standard result. In the case of relativistic jet-producing "magnetically arrested disks," we show that the negative energy and angular-momentum absorption condition is obeyed when the Blandford-Znajek mechanism is at work, and hence the high energy extraction efficiency up to ∼300% found in recent numerical simulations of such accretion flows results from tapping the black hole's rotational energy through the Penrose process. We show how black-hole rotational energy extraction works in this case by describing the Penrose process in terms of the Noether current.
- Publication:
-
Physical Review D
- Pub Date:
- January 2014
- DOI:
- 10.1103/PhysRevD.89.024041
- arXiv:
- arXiv:1310.7499
- Bibcode:
- 2014PhRvD..89b4041L
- Keywords:
-
- 04.70.Bw;
- 95.30.Sf;
- 95.30.Qd;
- 97.60.Lf;
- Classical black holes;
- Relativity and gravitation;
- Magnetohydrodynamics and plasmas;
- Black holes;
- General Relativity and Quantum Cosmology;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 24 pages, 14 figures, version published in Phys. Rev. D