What's with your name? Stars aren't black...


This is called a black hole. It is formed when a supermassive star has lost so much heat that its fusion is no longer able to create enough force to keep it from collapsing. A black hole is formed if the collapsing star is 13+ Sol's mass (I think). The reason it is called a black hole is because no light can escape, and therefore it looks like a hole of blackness.
Black holes are not actually completely black, but emit small amounts of radiation. They, however, black in visible light.
It is also sometimes called a black star.
Also, no, I didn't get this from Wikipedia, but rather from science class. Sadly, I don' remember most of it, so I couldn't give you the exact details... I know that the repellative forces of protons and/or electrons are somehow involved, but I forget exactly how.