What is a Black Hole? A black hole is a place in space where so much gravity is pulled, that even light can not get out.
Black holes can be big or small. Some scientists think the smallest black holes are as small as just one atom.
Scientists think the smallest black holes formed when the universe began. Stellar black holes are made when the center of a very big star falls upon itself.
A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole.
Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that. Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun.
NASA is using satellites and telescopes that are traveling in space to learn more about black holes. These spacecraft will hopefully help scientists answer more questions about black holes and the universe.