This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Black holes, despite their extreme nature, are described by surprisingly few basic parameters: their mass, charge and spin. Two black holes may have formed for completely different reasons and passed through very different histories, yet still end up in the same final state.
John Wheeler summarized this idea with the famous phrase "black holes have no hair." Once quantum physics enters the picture, things become more complicated. As Stephen Hawking showed in the 1970s, black holes have a temperature and produce what we now call Hawking radiation. For a stationary black hole, this radiation has a characteristic temperature related to the surface gravity.
The real universe is much less ideal. Finding a completely isolated black hole is not easy. Matter may fall toward it, a nearby companion may disturb the surrounding spacetime, or external fields may change.
For some period of time, the black hole can therefore be away from its quiet stationary state. Our paper, published in the journal Classical and Quantum Gravity, focuses on exactly that situation. We begin with an ideal, quiet black hole.
Then, for some finite period, it is disturbed in a preferred direction. Once the disturbance has passed, the black hole settles down again. Much later, we look at the system once more and ask a simple question: Can the Hawking radiation tell us something about what happened during the disturbance?
A useful way to study Hawking radiation is to follow outgoing light rays backward through spacetime. As we trace them toward the black hole, they undergo a very large redshift. The history of that redshift is one of the main ingredients in the Hawking calculation.
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