What exactly is a black hole?
I wrote this after looking at a gallery here on ebaumsworld of the Large Hadron Collider and becoming curious as to what it does and why they would build it. This led me on a journey along the internet to read about black holes. I figured if I was wondering about this thing, then surely the other viewers would be also...so here I am. Telling you the basics of what you'd want to know about a black hole! ;)
A black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape its pull after having fallen past its event horizon. This is in part why we call these a black hole.
How are black holes even made? A black hole is born when an object becomes unable to withstand the compressing forces of its own gravity. Many objects (including our Earth and Sun) will never become black holes themselves. Their gravity is not sufficient to overpower the atomic and nuclear forces of their interiors, which resist compression. but in more massive objects, gravity ultimately wins. Stellar-mass black holes are born with a bang. They form when a very massive star (at least 25 times heavier than our Sun) runs out of nuclear fuel. The star then explodes as a supernova. What reamins is a black hole, usually only a few times heavier then our Sun since the explosion has blown much of the stellar material away.
How big is a black hole? All matter in a black hole is squeezed into a region of infinitely small volume, called the cetral singularity. The event horizon is an imaginary sphere that measures how close to the singularity you can safely get. Once you have passed the event horizon, it becomes impossible to escape: you will be drawn in by the black hole's gravitational pull and squashed into singularity. The size of the event horizon (called the Scwarschild radius, after the German physicist who discovered it while fighting in the first World War) is proportional to the mass of the black hole. Astronomers have found black holes with even horizons ranging from six miles to the size of our solar system. but i prinicple, black holes can exist with even smaller or larger horizons. By comparison, the Schwarzschild radius of the earth is about the size of a marble. this is how much you would have to compress the Earth to turn it into a black hole. A black hole doesn't have to be very massive, but it does need to be very compact!
Since the creation of the Large Hadron Collider, the thoughts of a black hole forming on our beloved planet has been a concern by many. Some scientists fear that this could create Micro black holes. These would not be life threatening as they would most likely decay at an extremely fast rate. Though they would emit possibly dangerous levels of Hawking radiation. Even if micro black holes could be created, it would require a ring accelerator about 1000 light years in diamater! I don't see us building one of those anytime soon (Earth doesn't even have a diamater of .0001 of a light year).
Here's a list of pictures of black holes in outer space (these are all safe links, don't worry):
Check out my gallery here also if you want to see some more pictures.
Sure this may not be the most definitive work on black holes, but it kind of gives you the basics. Enough to know if you were just curious about them a little.
This site has a lot of good information on black holes.