Uniqueness of the Newman–Janis Algorithm in Generating the Kerr–Newman Metric

S. P. Drake, Peter Szekeres

Research output: Contribution to journalArticlepeer-review

104 Citations (Scopus)


After the original discovery of the Kerr metric, Newman and Janis showed that this solution could be "derived" by making an elementary complex transformation to the Schwarzschild solution. The same method was then used to obtain a new stationary axisymmetric solution to Einstein's field equations now known as the Kerr-Newman metric, representing a rotating massive charged black hole. However no clear reason has ever been given as to why the Newman-Janis algorithm works, many physicist considering it to be an ad hoc procedure or "fluke" and not worthy of further investigation. Contrary to this belief this paper shows why the Newman-Janis algorithm is successful in obtaining the Kerr-Newman metric by removing some of the ambiguities present in the original derivation. Finally we show that the only perfect fluid generated by the Newman-Janis algorithm is the (vacuum) Kerr metric and that the only Petrov typed D solution to the Einstein-Maxwell equations is the Kerr-Newman metric.

Original languageEnglish
Pages (from-to)445-457
Number of pages13
JournalGeneral Relativity and Gravitation
Issue number3
Publication statusPublished - Mar 2000
Externally publishedYes


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