Image: In this image, we see the exact center of our galaxy, known as the Central Molecular Zone. In addition to its scientific interest, this image won first prize in the AUI/NRAO photographic competition of the year 2008. Credit: A. Ginsburg (U. Colorado - Boulder) et al., BGPS Team, GLIMPSE II Team.
A black hole is a place in space where gravity is very, very strong. It is as if it were a huge vacuum cleaner that sucks up everything that is close to it. Imagine throwing a ball into a black hole, it would never bounce and come out. She would be sucked into the black hole.
Black holes are formed when very, very large stars die and collapse in on themselves. This creates a very dense area where the gravity is so strong that nothing can escape. This means that even light cannot get out of the black hole, which is why it is called "black".
Black holes are very special and fascinating because we cannot see them directly. We can only observe them indirectly by watching how the stars and planets around them move. Scientists are trying to find out more about black holes by using special telescopes and doing calculations.
Even though black holes may seem scary, there isn't one near our planet, so we have nothing to worry about. In fact, they are very important in understanding how our universe works and how stars and planets are formed.