I just viewed millions of black holes while watching Nova on PBS tonight. Using the latest graphics the show helped visualize galaxies and black hole gravitational pulls. They also used time lapsed graphics to show the future meeting of the Milky Way galaxy and our nearest galaxy, Andromeda as they rotate around each other and finally merge as a bigger galaxy centered by a larger black hole.
They now know that every galaxy has a black hole at the center. The black holes act like huge vacuum cleaners sucking up space and matter, yet they don't do this at a constant rate, going through a series of starvation and gluttonous stages. When a black hole can't handle everything being sucked up it will develop a expulsion stream that fires out the excess energy, which can be seen by telescopes on Earth.
Matter being sucked toward a black hole increase speed the closer the approach. A solar system closing in on a huge galaxy/black hole will speed up as it spirals into the black hole. Telescopes have been tracking the solar systems in the center of our galaxy and know where the black hole is.
It was fun to listen to the astronomers try to describe a black hole, it's not easy in layman's terms, but the show does describe them well. One guy suggested that falling into a black hole would be a good way to die. As you fall your atoms begin to fall at different rates of speed causing you to elongate and to be pulled apart. The bigger the black hole the slower in time this occurs which would allow a person to experience the fall into the black hole. What a way to go, blackholed.
Link to NOVA, from PBS.