Physics/Astronomy question about black holes

[dilsfunspot]

So a friend of mine and me were speculating about black holes. He theorized that black holes led to a 4th dimension. From that i started to question what black holes really are and how they "work". So heres my question:

 

From what i have learned my whole life, black holes form from stars or other masses that have so much mass and gravity at 1 point that they cave in on themselves and create a hole that will suck in everything around it which will never be seen again including light. Could it be similar to taking a piece of paper, laying it out straight in mid air, and pushing a pencil in the top until the paper bends down further and further and eventually rips making a hole? Perhaps the universe is a "plane" and nothing can escape because anything that travels over it falls through, meaning that light traveling across would also drop down? perhaps dimensions are laying ontop of eachother and this amount of bend in space connects the 2 dimensions through the hole that is created, which would mean in the 4th dimensions universe the opposite of a black hole is happening where instead of everything being pulled in, its being pushed away explaining why light goes in but dosnt come out.?

 

Thats just a few speculations i had and was wondering if any of them were moderately right/possible or maybe someone could tell me how it really works, i would appreciate it.

 

 

 

[ajb]

From what i have learned my whole life, black holes form from stars or other masses that have so much mass and gravity at 1 point that they cave in on themselves and create a hole that will suck in everything around it which will never be seen again including light.

 

So, very "untechnically"...

 

black holes are formed when the gravitational collapse of objects over comes any supporting mechanisms. Basically the gravitational field is so strong that the object collapses to a point; this is the singularity of a black hole.

 

As far as we know, under reasonable physical conditions, any such collapse is accompanied by an event horizon. That is a shell around the singularity for which the gravitational force becomes strong enough so that not even light can escape from. Loosley, the escape velocity is the speed of light right at this horizon, so nothing can gain enough kinetic energy to escape.

 

Now, when a black hole is formed, it is not like a giant vacuum cleaner. In fact, if our Sun were to turn into a black hole right now, we would not feel any gravitational difference. The sky would go dark in a few moments, but gravitationally we would still orbit around the black hole Sun as if nothing happened. It is not like the Sun would become "gravitationally stronger" and start to suck everything in.

 

Could it be similar to taking a piece of paper, laying it out straight in mid air, and pushing a pencil in the top until the paper bends down further and further and eventually rips making a hole? Perhaps the universe is a "plane" and nothing can escape because anything that travels over it falls through, meaning that light traveling across would also drop down? perhaps dimensions are laying ontop of eachother and this amount of bend in space connects the 2 dimensions through the hole that is created, which would mean in the 4th dimensions universe the opposite of a black hole is happening where instead of everything being pulled in, its being pushed away explaining why light goes in but dosnt come out.?

 

This makes me think of wormholes, that is space-times with non-trivial topology. It could be possible that the universe is filled with "tunnels" that connect different regions and these may be short cuts. Though such things pose interesting questions and may allow time travel!

 

[Delta1212]

It's important to emphasize that a black hole is not actually a hole, and it does not suck things in. Unless your definition of "hole that sucks things in" also happens to include the Earth.

 

Being slightly more technical than ajb, but still trying to avoid being too technical:

 

The strength of something's gravitational pull increases the closer you are to its center point. As you get further away, the strength gradually fades. There is one caveat, however: once you reach the surface of something, the strength stops increasing as you move to the center. This is because, once you start moving through the object, you start decreasing how much of it is below you pulling you down.

 

When a star collapses, it gets very, very small, but it still has all that gravity that the star had before. Only now, the surface of the star is very, very close to the center of the star. This means that you can get extremely close to the star's center, to an area that used to be inside the star, without reaching the star's surface. Gravity will be very strong here.

 

This area where gravity is so strong that nothing can escape is always smaller than the size of the star before it collapsed. Anything further away will not, as ajb said, be able to tell the difference. This is because the strength of a black hole's gravity does not increase from when it was a star, it's just that you can get much closer because it is smaller, and the closer you get, the more you feel the pull.

Edited May 9, 2013 by Delta1212