http://arxiv.org/abs/1310.7499
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 and show that the necessary and sufficient condition for extraction of black-hole’s rotational energy is analogous to that in 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 $\sim 300%$ found in recent numerical simulations of such accretion flows results from tapping of 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.
Date added: Wed, 30 Oct 13
You must be logged in to post a comment.