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 jetproducing "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.

Spectra of black hole accretion models of ultraluminous X-ray sources

“…The models are highly jet-dominated, as is evident from Figure 10. The jets clearly receive their power from the spinning BH via the Blandford & Znajek (1977) mechanism (which can be understood as a generalized version of the Penrose 1969 process, see Lasota et al 2014). The funnels in these models are quite empty of gas (even in the case of the model withṀ = 36Ṁ Edd ), presumably because the gas is rapidly blown away by the powerful jet.…”

Spacetime approach to force-free magnetospheres

“…For further discussion of the relationship between the Penrose and BZ processes see e.g. (Komissarov 2009;Lasota et al 2014).…”

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…This review does not deal with jet-launching processes nor with the general properties of jets and their relation to accretion disks. These topics are reviewed and studied in many other papers where more references can be found (e.g., Mirabel & Rodríguez 1999;Fender & Belloni 2004;Ferreira et al 2006;Livio 2011;Fender & Belloni 2012;Pudritz et al 2012;McKinney et al 2013;Zanni & Ferreira 2013;Frank et al 2014;Lasota et al 2014;Lovelace et al 2014;McKinney et al 2014). I assume that whenever the accreted gas has a large enough specific angular momentum jets are launched.…”