Blandford–Znajek process

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The Blandford–Znajek process is a mechanism for the extraction of energy from a rotating black hole,[1] introduced by Roger Blandford and Roman Znajek in 1977.[2] It is one of the best explanations for the way quasars are powered.[3] It requires an accretion disc with a strong polar magnetic field around a spinning black hole. The magnetic field extracts spin energy and the power can be estimated as the energy density at the speed of light cylinder times area:

P=B^{2}\left({\frac {r}{r_{c}}}\right)^{4}r_{c}c={\frac {B^{2}r^{4}\omega ^{2}}{c}}

where B is the magnetic field strength, r_{c} the speed of light radius and ω the angular velocity.[4]

References

  1. ↑ Frolov, Valeri P.; Zelnikov, Andrei (2011), Introduction to Black Hole Physics, Oxford: Oxford University Press, ISBN 978-0-19-969229-3, Zbl 1234.83001 , (Chapter 8.9: Black Holes in External Magnetic Field)
  2. ↑ R. D. Blandford and R. L. Znajek, "Electromagnetic extraction of energy from Kerr black holes", Mon. Not. R. Astr. Soc. 179:433-456 (1977)
  3. ↑ http://everything2.com/title/Blandford%2520Znajek%2520process
  4. ↑ Relativistic Astrophysics and Cosmology Lecture Notes, A. Lasenby, Cambridge University, 2010-2011.


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