Black Hole

 A black hole is a place where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. 

Black hole, cosmic body of extremely intense gravity from which nothing, not even light, can escape. This can happen when a star is dying.

When such a star has exhausted the internal thermonuclear fuels in its core at the end of its life, the core becomes unstable and gravitational collapse inward upon itself, and the star's outer layers are blown away.

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." It's 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 galaxy is called the Milky Way.

The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains supermassive black hole at it's 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 a few million Earths.

Source: Nasa