A Caltech Library Service

Electromagnetic extraction of energy from Kerr black holes

Blandford, R. D. and Znajek, R. L. (1977) Electromagnetic extraction of energy from Kerr black holes. Monthly Notices of the Royal Astronomical Society, 179 (3). pp. 433-456. ISSN 0035-8711. doi:10.1093/mnras/179.3.433.

[img] PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


When a rotating black hole is threaded by magnetic field lines supported by external currents flowing in an equatorial disc, an electric potential difference will be induced. If the field strength is large enough, the vacuum is unstable to a cascade production of electron–positron pairs and a surrounding force-free magnetosphere will be established. Under these circumstances it is demonstrated that energy and angular momentum will be extracted electromagnetically. As a further consequence it is shown that charge can never contribute significantly to the geometry of a rotating hole. The fundamental equations describing a stationary axisymmetric magnetosphere are derived and the details of the energy and angular momentum balance are discussed. A perturbation technique is developed which can be used to provide approximate solutions for slowly rotating holes. Solutions appropriate when the field lines threading the hole lie on conical and paraboloidal surfaces at large distances are described to illustrate this mechanism. These ideas are incorporated into a discussion of a model of active galactic nuclei containing a massive black hole surrounded by a magnetized accretion disc. In this model relativistic electrons can be accelerated at large distances from the hole and therefore will not incur serious losses, which is a defect of some existing models. In addition, if the field lines have paraboloidal shape, the energy will be beamed along antiparallel directions as observations of both compact and extended radio sources seem to require.

Item Type:Article
Related URLs:
URLURL TypeDescription
Blandford, R. D.0000-0002-1854-5506
Additional Information:© 1977 Royal Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1976 July 15. We thank J. P. Arons, G. W. Gibbons, S. W. Hawking, D. Lynden-Bell and M. J. Rees for useful discussions. RZ acknowledges an SRC studentship.
Funding AgencyGrant Number
Science Research Council (SRC)UNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20190521-165453698
Persistent URL:
Official Citation:R. D. Blandford, R. L. Znajek, Electromagnetic extraction of energy from Kerr black holes, Monthly Notices of the Royal Astronomical Society, Volume 179, Issue 3, 1 July 1977, Pages 433–456,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95672
Deposited By: George Porter
Deposited On:22 May 2019 22:33
Last Modified:16 Nov 2021 17:14

Repository Staff Only: item control page