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See this, it might interest you.https://www.simonsfoundation.org/quanta/20121221-alice-and-bob-meet-the-wall-of-fire/
There is simply no single answer to your question, it is still speculative. This is why it is so interesting... )
If gravity propagates at the speed of light, and everything inside the event horizon is governed by that limit, how can the mass of the black hole be evident or measureable to the outside world? On the other hand, if gravity were to propagate at c and above, I could understand gravity's appearance beyond the event horizon. If the speed of gravitational propagation is less than c, how can the mass of a black hole gravitationally influence another body in space?
Let's imagine we're parked at a safe orbital distance for a supermassive black hole. The mass of the black hole is producing gravitational energies that originate within the event horizon, depending upon the aggregate mass it contains. Because the speed of gravity is the same as light, how does this energy reach beyond the event horizon?
Purely in terms of general relativity, there is no problem here. The gravity doesn't have to get out of the black hole. General relativity is a local theory, which means that the field at a certain point in spacetime is determined entirely by things going on at places that can communicate with it at speeds less than or equal to c. If a star collapses into a black hole, the gravitational field outside the black hole may be calculated entirely from the properties of the star and its external gravitational field before it becomes a black hole. Just as the light registering late stages in my fall takes longer and longer to get out to you at a large distance, the gravitational consequences of events late in the star's collapse take longer and longer to ripple out to the world at large. In this sense the black hole is a kind of "frozen star": the gravitational field is a fossil field. The same is true of the electromagnetic field that a black hole may possess.
The GR black hole is probably wrong because a valid theory of quantum gravity is necessary to solve the problem.
Quote from: Ethos_ on 19/12/2013 22:59:17If gravity propagates at the speed of light, and everything inside the event horizon is governed by that limit, how can the mass of the black hole be evident or measureable to the outside world? On the other hand, if gravity were to propagate at c and above, I could understand gravity's appearance beyond the event horizon. If the speed of gravitational propagation is less than c, how can the mass of a black hole gravitationally influence another body in space?The answer is that (classically) gravity doesn't propagate outward from a black hole. The gravitational field formed as the star collapsed into a black hole and it stays in existence after the black hole forms. In a sense, it would seem to be emanating out from the event horizon, since classically nothing inside the event horizon could communicate to the external universe.
First of all you made the question more complex than it needs to be. There’s no need to talk about supermassive black holes. Any black hole will do. Basically you want to know how gravitons escape from the event horizon, correct? John Baez answered this question in the Usenet FAQ at http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html
I'm not sure of this, but reading Baez there, Pete, the argument seems to become one of 'time dilations', comparing over frames of reference? I think it's one way to look at it, but to me 'gravity' also seems as a 'net', updated at 'c'? And the Black Hole, passing the event horizon becoming a place where that net becomes a 'infinite well'? That though is a question of geometry, isn't it? Do I really need gravitons to define this?
What is the temperature of a black hole, is it hot or very cold, does it lose it's heat at the point of formation. Once it has formed it cannot lose anymore heat.
What is the temperature of a black hole? The AnswerThe temperature of a black hole is determined by the 'black body radiation temperature' of the radiation which comes from it. (e.g., If something is hot enough to give off bright blue light, it is hotter than something that is merely a dim red hot.) For black holes the mass of our Sun, the radiation coming from it is so weak and so cool that the temperature is only one ten-millionth of a degree above absolute zero. This is colder than scientists could make things on Earth up until just a few years ago (and the invention of a way to get things that cold won the Nobel prize this year). Some black holes are thought to weigh a billion times as much as the Sun, and they would be a billion times colder, far colder than what scientists have achieved on Earth. However, even though these things are very cold, they can be surrounded by extremely hot material. As they pull gas and stars down into their gravity wells, the material rubs against itself at a good fraction of the speed of light. This heats it up to hundreds of millions of degrees. The radiation from this hot, infalling material is what high-energy astronomers study. David Palmerfor Ask an Astrophysicist
Once it has formed it cannot lose anymore heat.