A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

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Gamma-ray bursts: A supernova connection

Can the gamma ray bursts connected to a new supernova prevent the black hole from forming? Quoting the abstract of the linked reference "...has become clear that probably all long GRBs are ...
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Big Bang snuffed by a black hole?

Wasn't the density of the universe at the moment after the Big Bang so great as to create a black hole? If the answer is that the universe/space-time can expand anyway what does it imply about what ...
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Black Hole Singularities

If two black holes collide and then evaporate, do they leave behind two naked sigularities ore? If there are two, can we know how they interact?
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Is there a black hole in the centre of the Milky Way?

Is it true that the whole galaxy is actually revolving, and powered by a black hole? Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the ...
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What is the color shift if light passes between two (or more) black holes?

If we observe light that originates X light years away, but it passes between black holes X/2 light years away, will it be normal or red shifted or blue shifted? What if the black holes were X/4 or ...
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Double slit experiment near event horizon

What happens if you perform a double slit experiment near an event horizon, if one of the slits is outside, one is inside the event horizon?
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How fast a (relatively) small black hole will consume the Earth?

This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth". Consider a small black hole, that is somehow got inside the Earth. Under ...
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Do all massive bodies emit Hawking radiation?

It is known that any accelerated observer is subject to a heat bath due to Unruh radiation. The principle of equivalence suggests that any stationary observer on the surface of a massive body should ...
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The final death of a black hole

What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and ...
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How do you explain the observed fact that “black hole” objects move?

As per Newton objects with mass attract each other, and per Einstein this is further explained by saying that mass warps space-time. So a massive object makes a "dent" into space-time, a gravity well. ...
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Supermassive black holes with the density of the Universe

This question was inspired by the answer to the question "If the universe were compressed into a super massive black hole, how big would it be" Assume that we have a matter with a uniform density ...
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How precisely does a star collapse into a black hole?

I think we all heard general statements like "once big enough star burns out there is nothing to prevent the gravitational collapse ending in a black hole". But I can't remember even seeing the ...
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If the universe were compressed into a super massive black hole, how big would it be?

I understand only a little of general relativity, but that's why I'm here! :) Consider the hypothetical situation of some extra-terrestrial intelligence pushing all the mass in the universe, every ...
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What kind of systems of black holes satisfy the laws of black hole thermodynamics?

I've come across black holes thermodynamics multiple times recently (both at this site and elsewhere) and some things started bugging me. For one thing, first law bothers me a little. It is a ...
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White Holes and Time-Reversed Oppenheimer-Snyder collapse

So, the canned explanation that I always hear about why the white hole solution of the extended Schwarzschild solution is non-physical is that "The matter distribution cuts off the white hole ...
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If I fall into an evaporating black hole, where do I end up?

This question has been bothering me for a while. I have a crude hypothesis... As I understand it, an observer falling into a black hole will cross the event horizon at some specific future (proper) ...
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How does gravity escape a black hole?

My understanding is that light can not escape from within a black hole (within the event horizon). I've also heard that information cannot propagate faster than the speed of light. It would seem to ...
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Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?

If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect ...