Is a black hole considred a black body?

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Discussion Overview

The discussion centers around whether a black hole can be considered a black body, exploring the theoretical implications and characteristics of both concepts. It involves aspects of theoretical physics, particularly relating to black hole thermodynamics and radiation.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that black holes emit Hawking Radiation, which has a black body spectrum, suggesting that black holes behave like black bodies in this context.
  • Others argue that while black holes can be considered in terms of black body radiation, they have a very low emissivity coefficient that varies with size, and that non-rotating black holes of the same size have the same temperature, while rotating ones are hotter.
  • A participant notes that the analogy of a black hole as a black body is not entirely accurate, emphasizing that a black body is a classical physics concept, whereas a black hole is a construct of general relativity, possessing some similar properties but differing fundamentally.

Areas of Agreement / Disagreement

Participants express differing views on the analogy between black holes and black bodies, with some supporting the comparison based on Hawking Radiation and others challenging its validity due to the differing nature of the two concepts. The discussion remains unresolved.

Contextual Notes

There are limitations regarding the definitions of black bodies and black holes, as well as the assumptions underlying the analogy. The discussion does not resolve the mathematical or conceptual nuances involved.

Starwatcher16
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Is a black hole considered a black body?
 
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The Hawking Radiation that black holes are supposed to emit (though this hasn't been directly observed yet I believe) has as black body spectrum. In that sense a black hole behaves like a 'black body', although perhaps there are other characteristics of the formal definition of a black body that a black hole does not satisfy? I'm not sure.
 
Current theory is that you CAN consider it that way. It just has a really low emissivity coefficient (which also happens to vary with its size) AND all non-rotating black holes of the same size have the same temperature, and rotating ones are hotter.
 
Starwatcher16 said:
Is a black hole considered a black body?

As Wallace and fleem have noted, Hawking showed that black holes radiate in (close to) black body-like fashion. Taking a black hole to be a black body and using some hand waving leads to

https://www.physicsforums.com/showthread.php?t=205711.
 
It's really not a good analogy. A blackbody is an entity in classical physics. A black hole is a construct of general relativity. It posseses some of the same properties, but is not of the same species.
 

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