In the center of galaxies is common to have a black Hole. In our galaxy there is a black hole about 22,5 million kilometers across which isn't big compared to other galaxies that have much bigger black holes. A black hole is place in space where gravity pulls so strong that light itself can't escape. Black holes are formed when an object, any object's mass is condensed so much that its gravity causes it to collapse into itself. ANYTHING can become a black hole.