Penrose process

The Penrose process (also called Penrose mechanism) is theorised by Sir Roger Penrose as a means whereby energy can be extracted from a rotating black hole.[1][2][3] The process takes advantage of the ergosphere – a region of spacetime around the black hole dragged by its rotation faster than the speed of light, meaning that from the point of view of an outside observer any matter inside is forced to move in the direction of the rotation of the black hole.[4]

Trajectories of bodies in a Penrose process

In the process, a working body falls (black thick line in the figure) into the ergosphere (gray region). At its lowest point (red dot) the body fires a propellant backwards; however, to a faraway observer both seem to continue to move forward due to frame-dragging (albeit at different speeds). The propellant, being slowed, falls (thin gray line) to the event horizon of the black hole (black disk). The remains of the body, being sped up, fly away (thin black line) with an excess of energy (that more than offsets the loss of the propellant and the energy used to shoot it).

The maximum amount of energy gain possible for a single particle decay via the original (or classical) Penrose process is 20.7% of its mass in the case of an uncharged black hole (assuming the best case of maximal rotation of the black hole).[5] The energy is taken from the rotation of the black hole, so there is a limit on how much energy one can extract by Penrose process and similar strategies (for an uncharged black hole no more than 29% of its original mass;[6] larger efficiencies are possible for charged rotating black holes[7]).

  1. ^ Penrose, R.; Floyd, R. M. (February 1971). "Extraction of Rotational Energy from a Black Hole". Nature Physical Science. 229 (6): 177–179. Bibcode:1971NPhS..229..177P. doi:10.1038/physci229177a0. ISSN 0300-8746.
  2. ^ Misner, Charles W.; Thorne, Kip S.; Wheeler, John Archibald (1973). Gravitation. San Francisco: W. H. Freeman. ISBN 978-0-7167-0334-1.Misner, Thorne, and Wheeler, Gravitation, Freeman and Company, 1973.
  3. ^ Williams, R. K. (1995). "Extracting X rays, Ύ rays, and relativistic e−e+ pairs from supermassive Kerr black holes using the Penrose mechanism". Physical Review D. 51 (10): 5387–5427. Bibcode:1995PhRvD..51.5387W. doi:10.1103/PhysRevD.51.5387. PMID 10018300.
  4. ^ Cui, Yuzhu; et al. (2023). "Precessing jet nozzle connecting to a spinning black hole in M87". Nature. 621 (7980): 711–715. arXiv:2310.09015. Bibcode:2023Natur.621..711C. doi:10.1038/s41586-023-06479-6. PMID 37758892. S2CID 263129681.
  5. ^ Chandrasekhar, Subrahmanyan (1983). The Mathematical Theory of Black Holes. Clarendon Press. p. 369. Bibcode:1983mtbh.book.....C. ISBN 0-19-851291-0.
  6. ^ Carroll 2004, p. 271
  7. ^ Bhat, Manjiri; Dhurandhar, Sanjeev; Dadhich, Naresh (1985). "Energetics of the Kerr-Newman black hole by the penrose process". Journal of Astrophysics and Astronomy. 6 (2): 85–100. Bibcode:1985JApA....6...85B. CiteSeerX 10.1.1.512.1400. doi:10.1007/BF02715080. S2CID 53513572.