Black holes generate energy and radiation (light) from the matter that falls onto them. They accrete matter from orbiting celestial objects such as stars, planets, asteroids, comets, and other forms of debris. This accreted matter falls onto the black holes through their accretion disks and these disks produce the energy and radiation (light). This is the reason why we can "see" black holes, because we don't actually see the black hole we see the accretion disk. If there was not matter accretion producing radiation (light) there would not be any light emitted from a black hole, hints the "black" hole. Here is a black hole; as you can see the very center is dark and the outer parts a luminous.
A black hole in a dwarf galaxy effects its surroundings differently than a black hole in a regular galaxy. A black hole in a dwarf galaxy changes the speed of the objects a lot. It effects many more objects in a dwarf galaxy than a regular galaxy because a regular galaxy is much bigger and more spaced out than a dwarf galaxy. Here is a picture of our Milky Way; the picture shows a band of stars left over by a dwarf galaxy collision with our Milky Way (seen in the blue). This leads astronomers to believe the Milky Way formed from a number of dwarf galaxies, that in previous years collided with one another.
