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Before Hawking radiations were discovered, people said black holes had no temperature even though we could extract energy from them using the Penrose process (which also leads to a relation similar to the first law of thermodynamics).

Could someone explain to me why, when we thought that black holes could not radiate, we said they have no temperature?

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Hawking radiations has never been observed, there were theorized, not discovered (it is a big difference). Black holes are regions of space-time, not objects. So the only way for a space-time region to have temperature is by radiations. Hence when we thought black holes could not radiate, we thought that they had no temperature at all.

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  • $\begingroup$ Your answer to my question "why, when we thought that black holes could not radiate, we said they have no temperature" is "when we thought black holes could not radiate, we thought that they had no temperature at all."? Do you feel that this is an answer? $\endgroup$ – Y2H Jun 23 '20 at 17:55
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    $\begingroup$ My answer to your question is above this sentence you picket off its context. $\endgroup$ – Jeanbaptiste Roux Jun 23 '20 at 17:58

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