I have just read (in the black holes chapter 14 on p244 of this book Ref.1) that in string theory, when one adds an (electric?) charge $Q$ to a static black hole, one can arrive at an exotic supersymmetric black hole. This sentence is not explained further and there are several (I think related enough) things I dont understand about it, which can be summerized under the question what really is an exotic suppersymmetric black hole?

First, how exactly does the addition of a charge (if it is not outright a supercharge) lead to supersymmetry?

Second, what is meant by an exotic black hole, conversely to for example an extremal black hole that has just the maximum charge allowed given its mass?

Third, what does it mean for a black hole to be supersymmetric anyway?


  1. D. McMohan, String Theory Demystified, McGraw-Hill, 2009
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    $\begingroup$ Can you provide a link to or quote the source? Context may help. $\endgroup$ – Brandon Enright May 25 '13 at 16:58
  • $\begingroup$ @BrandonEnright ok, I have even found a PDF of the book and put it into the question. $\endgroup$ – Dilaton May 25 '13 at 18:03
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    $\begingroup$ @Dilaton: It is best to supply title, author, etc, of link, so we can reconstruct the link in case of future link rot. $\endgroup$ – Qmechanic May 25 '13 at 19:08
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    $\begingroup$ @Dilaton I've heard that extremal black holes are solitonic solutions of supergravity, preserving some degree supersymmetry. I myself do not understand what it means, but I know it is important. $\endgroup$ – Prathyush May 26 '13 at 3:09
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    $\begingroup$ Dear Dilaton, the adjective "exotic" in front of a black hole isn't a technical term with a particular meaning. It just means that, subjectively to the author, the black hole is unusual for the author of the sentence, usually because she is used to Schwarzschild-like neutral black holes from the undergrad courses. At any rate, there exists a maximum Q given a fixed mass for which the black hole is "extremal" and such black holes often preserve a part of the supersymmetry (if it was there to start with), have infinite throats near the event horizon, and other qualitative differences from neutr. $\endgroup$ – Luboš Motl May 26 '13 at 4:56

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