This is an image of presumed black hole taken with x-rays. It's incredibly bright and is found in constellation of the Swan Cygnus. The bright blue to the left is a star, with an estimated 30 times the mass of our sun. Apparently, this candidate for a black hole was formed without a supernova, so astronomers aren't sure if it actually IS a black hole. The picture above is an artist's interpretation of the system, but it based off of the viewable processes occuring in the system. It is viewable with a regular telescope, but not with this detail.
Black holes have incredibly strong gravitational pulls and are only viewable from the movement of celestial things around it. They don't reflect any light so they appear to be solid and black, even though they are made, essentially, of nothingness. They also radiate, and the temperature goes down as the mass of the black hole goes up, so it's nearly impossible to detect radiation from black holes born of stellar mass. Astronomers spectate that at the center of the Milky Way galaxy a supermassive black hole is pulling everything to itself. Since black holes have no viewable surface, the point where any event on the other side is not viewable to the observer is called the "event horizon". No light or matter emitted beyond the horizon is viewable past the event horizon.
HOW IT APPLIES TO CLASS:
We've been studying the evolution of stars, and this APOD is very much in that line of study. I'd say it's a prime example of the fact that astronomers really aren't sure about a lot of stuff, but in the long run it doesn't matter (but it is interesting and neccessary for feeding curious minds), because we probably aren't going to get sucked into the candidate any time soon.