A black hole is a place in space where gravity pulls so much that even light cannot escape. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.
Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.
Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object.
Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way.
The largest black holes are called "supermassive." These black holes have masses that are more than a million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called ‘Sagittarius A’. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths
For a particle to escape a black hole, a quantum fluctuation must occur near a black hole's edge. When this happens, sometimes one particle will tunnel out before the annihilation can take place. Its partner immediately gets "spaghettified" by the black hole elongated as it plunges to the center, in short there is little change of an escape from a black hole’s pull other than this described escape.
As matter crosses the event horizon of a black hole it gets compressed down to Atoms and beyond, But, even before that happens the gravitational tidal force will rip off the electrons and have the nucleus break up and have most of it converted to neutrons, and then rip those off and get to the quarks, and eventually fall into the singularity. That's what is described to as a black hole forms when there is too much gravity, nothing can withstand the gravitational effects.
In 2019, images were captured of an apparent black hole with 6.5 billion times the mass of our sun in the center of the nearby M87 galaxy.
Due to the equivalence principle, an atom free falling into a blackhole is travelling inertially, and a comoving observer would not notice anything different about the atom, but the atom would not be appreciably changed, after that, the atom would collapse.
The basic principles of quantum mechanics are thought to govern all the other laws of nature, but when they are applied to black holes they lead to a contradiction, exposing a flaw in the current form of these laws. So powerful is this that it bends light around the center of a black hole.