Can we determine the rotation speed of a black hole?

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Discussion Overview

The discussion centers on the possibility of calculating the rotation speed of a black hole, exploring theoretical frameworks and observational methods related to black hole spin. It encompasses conceptual inquiries and technical explanations regarding the nature of black holes and their rotation.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the possibility of calculating the rotation speed of a black hole, noting a lack of information available online.
  • Another participant explains that a Kerr black hole has a theoretical rotation component due to angular momentum conservation, but emphasizes that this rotation cannot be measured directly as events inside the event horizon are unobservable.
  • A different participant mentions a theory suggesting that light emitted from the surroundings of a black hole could be used to calculate its rotation speed.
  • Further, another participant references a specific case involving an x-ray binary where the strength of an ultrasoft x-ray component may relate to the black hole's spin.
  • One participant expresses skepticism regarding the effectiveness of the methods proposed in the referenced literature for deriving a black hole's intrinsic spin.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and methods for determining black hole rotation speed, indicating that multiple competing theories and uncertainties remain in the discussion.

Contextual Notes

Participants highlight limitations in current understanding and measurement techniques, particularly regarding the unobservable nature of phenomena inside the event horizon and the reliance on indirect observational methods.

cosmicpencil
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Is it possible to calculate the rotation speed of a black hole? Idid not find anything on this on google.

thanks
 
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A Kerr black hole has a theoretical rotation component due to conservation of angular momentum. It cannot be measured directly as we cannot observe anything occurring inside the event horizon. I doubt it's meaningful to talk about rotataion with respect to the event horizon. For discussion, see
http://science.howstuffworks.com/black-hole.htm/printable
 
I heard in class of a theorie that would use the light emmited from the black hole surroundings to calculate the rotation speed, anyone familiar with these theories?
thanks
 
I heard about that. In an x-ray binary in which a black hole is believed to be the compact object, it has been suggested that the strength of an ultrasoft x-ray component is directly related to the black hole's spin.
Check out section 8.2 of the following:
http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.astro.44.051905.092532
 
Good link, maria, but, I am unconvinced the authors have derived an effective way to derive the intrinsic spin of a black hole.
 
thank you for this link.
 

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