A black hole is defined as an area of space with a gravitational field extremely severe that no matter or radiation can escape. Black holes can be small like an atom, or big like a large mountain. The huge black holes are known as supermassive, which have masses equal to more than 1 million suns together.
Black holes cannot destroy stars, moons and planets. Even the earth will not fall into a black hole as all the black holes are very far away from the Earth.
Types of Black Holes
There are basically three types of black holes: stellar, supermassive, and miniature black holes.
Stellar black holes are formed when a massive star collapses.
Supermassive black holes are equivalent to billions of suns, and expected to exist in the centres of most galaxies, including Milky Way galaxy. It is assumed that these black holes are a consequence of galaxy formation.
Miniature black holes are assumed to have been formed shortly after the “Big Bang”, which is predicted to have started the universe 13.7 billion years ago. During very initial stages of life of the universe, the rapid expansion of some matter is believed to have compressed slower-moving matter with such a force to contract into black holes.
Formation of Black Holes
Usually, a black hole is produced by some dying stars. There are many types of black holes, of which stellar mass black holes are most common. Stellar mass black holes develop when huge main sequence stars (approximately 10-15 times the mass of the Sun) run out of nuclear fuel in their cores. This results into a massive supernova explosion, which leaves a black hole core at the region where the star once existed.
During its lifetime of star, there is altercation between gravity pulling in and pressure pushing out. Outward pressure comes from the energy produced by nuclear reactions in the core of the star. But when a star becomes short of nuclear fuel, then gravity compresses the material in the core. In fact, the more massive the crux of the star, the greater is the gravitational force which compresses the material, crumpling it under its own pressure.