Basic Knowledge of Blackholes
A black hole is a place in space where gravity has such a strong pull that even light can’t get out. Gravity there is so strong because matter has been squeezed into a small space. This can occur when a star is dying. The fact that light can’t escape black holes means that people cannot see black holes. They are invisible, however, with high-tech space telescopes and other special tools, 
you may be able to view black holes.
How Big Are Black Holes?
Black holes can come in big and small sizes. The smallest black holes can be as tiny as one atom. One kind of black hole is called a “stellar black hole.” Its mass can be up to 20 times more than the sun. There may be many stellar black holes in Earth’s galaxy, the Milky Way.
How Do Black Holes Form
Stellar black holes are made when the center of a very big star collapses. This causes a supernova. A supernova is an exploding star that bursts out part of the star into space.
If Black Holes are Imperceptible, How Do We Know They are There?
A black hole can’t be seen because strong gravity pulls all of the light into the middle of the hole. However, scientists can see how the gravity affects the stars and gas around the black hole. When a black hole and star are close together, high-energy light is made. This kind of light can not be seen by the human eye. Satellites and telescopes in space are used to see the high-energy light. 
Could A Black Hole Destroy The Earth?
Earth will not fall into a black hole because no black hole is close enough to the solar system. Even if a black hole the same mass of the sun were to take the place of the Earth’s sun, Earth would not fall in. The black hole would have the same gravity as the sun therefore, Earth and other planets would orbit the black hole as they orbit the sun today. The sun will not turn into a black hole because the sun is not a big enough star to make a black hole.
Resources:
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
