Oh, you said holes.
1. The reason why black holes seem dark or black is because space falls into these singularities at a faster rate than the speed of light, therefore, not even light can escape.
2. Though it was once said by Steven Hawkins that all information that would fall into a black hole is lost to the universe forever, it has since been discovered that as matter falls into the black hole, it gets smeared across the event horizon, and the radiation that it gives off correlates to the matter falling into it.
3. There is believed to be super massive black holes at the center of most galaxies, including our own. In fact, this is how we discovered their existence, by observing the effects they have on stars near the center of our galaxy.
The core also sinks into the fabric of space-time, making a hole in it, which is why it's popularly used in science fiction as a means of time travel.
Schwarzschild - non-rotating black hole
Kerr - rotating black hole
Courtesy of science - how stuff works.
It also might be possible because of the tear it makes for one black hole to be booted into a complete and separate galaxy from its host - courtesy of science daily