by Arlos » Fri Aug 11, 2006 7:57 pm
The way a black hole works is somewhat hard to describe, at least without getting highly technical, but I'll give it a swing. There are two main types of black holes, those from collapsed high-mass stars, and the supermassive black holes that exist at the centers of galaxies (including our own). OK, first get some really basic stuff out of the way, then on to what black holes (one type anyway) really are.
Every object in the universe has mass, and thus has gravity. Even you, me, your dog, etc. The effect of gravity decreases by the square of the distance you are from the object. ie, if you go 2x as far away, the force will be 1/(2^2), or 1/4 as strong. Go 4x as far away, the force will be 1/(4^2), or 1/16 as strong, etc. Every object has associated with it what is known as an "Escape Velocity". This is the speed at which you need to travel to be able to reach a point far enough away from something that it won't be able to pull you back to it again. For the Earth, this is about 26,000 mph, if I remember right. Go slower than that, and eventually you'll fall back to earth. Now, a black hole is something where the escape velocity to get away from it is so high that it is higher than the speed of light.
We don't know how the supermassive ones formed, really, but with collapsed stars, basically it's the very last stage of the star dying. (We're talking huge stars here, like 100x bigger than the Sun). Now, every star exists in a delicate balance between gravity, from all of the mass that makes up the star, and pressure from the energy being created as the star fuses hydrogen into helium.
Well, eventually the hydrogen runs out, and for bigger stars, it runs out much faster, because it is burning much more of it. Once that fuel is used up, the pressure that is holding the star ves gravity is gone, and it collapses in on itself. There's a bunch of complex stuff that happens then, including fusing other atoms than hydrogen, but that's not important here. Eventually, the star runs out of everything that is possible to fuse and gain energy from, and all of the pressure is gone, and everything collapses inward.
At this point, the core of the star has become incredibly dense. So dense that a teaspoon's worth of the stuff would weigh more than the entire Empire State Building, for example. So, as all the accumulated stuff collapses in, it hits that ultra-dense core and most of it bounces and flies out at incredible speeds. This is what we see as a Supernova. However, gravity has not gone away, and all of the momentum of the stuff falling in causes that core to collapse even more than it already was. If there is enough mass (and enough gravity), that can ultimately rip the very fabric of space and create a black hole.
Now, I realize that that's kind of an odd concept, but a way to imagine it is this: think of the universe as a giant rubber sheet, stretched out really tightly. Now, if you put a basketball on that sheet, it's going to make a dent, right? If you put a bowling ball on it, it would make a much bigger dent, and the sides of the dent would be a lot steeper, yes? Now, imagine if you had a baseball that weighed as much as a bowling ball and put that on the sheet; it would make a deeper dent than the bowling ball, with even steeper sides, right? Now, to imagine a black hole, imagine if you dropped something that weighed as much as a Cadillac, but was no bigger than a marble onto that sheet. It'd make a HUGE almost straight-sided dent in that sheet, before ripping a hole in the bottom, right? Now lastly, imagine that dent stayed there, as if the super-heavy marble was still on the sheet, because even though it's ripped a hole in the sheet, it's still there, just on the other side of it.
Well, that's effectively what a black hole is, that super-steep dent in the fabric of the universe with a rip at the bottom. The sides of that dent are so steep that if you go over the edge, there's no getting out again. That edge of the cliff is what is known as the "Event Horizon", and it marks the point at which the escape velocity to get away from the black hole reaches the speed of light. At anything closer to the black hole than that Event Horizon, physics breaks down, it's entirely beyond our understanding, we have no idea what it's like in there, effectively it's not even part of our universe. Before that point, it's theoretically possible to go fast enough to get away, but practically, not likely, at least for anything larger than an individual atom, as I'll explain with another analogy.
OK, you've ridden on a roller coaster, right? Those corners that press you into your seat there are what, 2-3Gs? (meaning 2-3x the normal force of gravity) Now, think of how much force that felt like, and imagine if it was just the lower half of your body that was pulled that much, while your upper half wasn't. Would feel like you were getting stretched apart, and hurt like hell, right? Well, as you get close to a black hole, that slope I talked about is so steep, even before you reach the point of no return, that there can be literally HUNDREDS OF THOUSANDS times the force of gravity difference between your head and your feet. The term for what happens to you is called "Spaghettification", and is just what it sounds like. You get stretched out into a giant piece of spaghetti that is exactly 1 atom wide. Needless to say, that is not something that would be good for your health.
So, I realize this was long and complex, but hopefully answers your question. No, we couldn't live in, or even NEAR a black hole; we can't even get close to one. As for what it's like once you get inside the Event Horizon... Well, as I said, we simply don't know, because all of our physics breaks down. It might as well be entirely outside the universe.
-Arlos