One way of searching for a black hole is to look for areas of space that exhibit a large amount of mass in a small, dark space. In fact, most astronomers now believe that a super massive black hole may exist in the center of our own Milky Way galaxy. The black hole has the same mass as the original star that it was formed from. As long as nothing gets too close to the event horizon, it is safe. The evidence for this and other black holes can be confirmed by searching for x-rays.
Astronomers believe that black holes emit strong amounts of x-rays.
Many of the stars in our galaxy exist as binary star systems. Sometimes one of the two stars in a binary system becomes a black hole. When this happens, the black hole may begin to suck matter from the other star. This matter swirls around the black hole in a formation known as an acceleration disk, moving faster and faster as it nears the center. It is believed that this matter emits radiation in the form of x-rays as it enters the black hole and is crushed out of existence.