Black Hole Evaporation

[Rev. Green]

How does a black hole evaporate?
If it is not rotating and not charged then it can lose its mass by gamma ray Hawking radiation, but what if it is charged? The particle which removes the remaining mass might not neutralise the remaing charge.

[Count-A-Strong]

I havent a clue what your question really means but being the helpful soul I am, i found this which links to a downloadable document.
http://arxiv.org/abs/gr-qc/0010055
Hope it's some good as it's about 10 years old!

[Rev. Green]

Many thanks, I hadn't come across preferential emission (p22) before.

[Count-A-Strong]

Glad it was of some use.

[Kanny_Ken]

From what I remember of the first edition of Stephen Hawkins book, "A Brief History of Time" (I know it has been revised so this might not be what it says now) funny things happen at the event horizon of a black hole. According to the Heisenberg uncertainty pricinciple a particle and anti-particle can be spontaneously created and exist for a time equivalent to the uncetainty interval. In normal conditions they they mutally destroy each other and nothing is observed. However, when such a pair is created at the event horizon one of the particles can be trapped in the black hole and the other escape which can be observed as radiation. So if anything, the black hole gains mass out of nothing.

Weird and unbelievable? If you compare it with the way governments and bankers behaved the last two years it makes perfect sense. Hedge funds and quantitative easing make something out of nothing but us ordinary folk sure get weighed down by them!

[Rev. Green]

You have described it well Kanny_Ken except, in my understanding, the black hole loses the mass which the particle "owes" to the vacuum.
However, the problem is not how the black hole loses mass, but how it contrives to lose its charge and angular momentum at exactly the same time as it loses its mass.

[Garmard]

Always wondered Rev how black holes initially slow down time by mass and force of gravity. Could you explain in laymans terms please.....Thanks.

[Rev. Green]

If I could do that, Garmard, I'd be writing “A Short History of Time”, but all bigheads answer questions they know nothing about, so here goes:-
Suppose a spaceship which is painted green, inside and out, approaches a black hole at 100,000 mph. and assume that gravity is an attractive force between masses. (My personal view is different, but I'm in a tiny minority.)
As the spaceship approaches the black hole it is pulled towards it by the force of gravity, causing the spaceship to travel faster and faster. If the pilot disregards the inconvenience of being crushed to death, he will notice that his spaceship remained the same colour. This is important because the paint appears green because parts of it vibrate regularly. When it stays the same colour this shows that it is still vibrating at the same rate and so time has neither speeded up nor slowed down for the pilot. (continued...)

[Rev. Green]

Because of its speed, the spaceship and each speck of paint will travel nearly a three-hundredth of a millimetre for every million vibrations. Think of the spaceship as leaving a line of dots in space, nearly a three-hundredth of a millimetre apart. As the spaceship approaches the black hole, and its speed increases, the distance between consecutive dots will increase.
When an observer on Earth sees the spaceship, it will still appear green when the spaceship is a good distance from the black hole. This is because the extra time that the light takes to travel the distance between dots in not enough to alter its colour. However, once the spaceship it travelling quickly, the dots will be further apart and the extra time taken for the light to reach Earth will cause the ship to appear first yellow, then red. The observer on Earth, knowing that yellow and red light are produced by slower vibrations than green, will assume that time is slowing down for the spaceship. In the limit, when the dots are very far apart, the light will be very faint radio waves and the observer on Earth will think that time has almost stopped on the spaceship.