A black hole is a place in space where gravity is so strong that even light cannot get out. A black hole is a lot of matter squeezed into a very small space. Black holes are invisible, because no light comes out of them. Black holes do not roam around space eating stars and planets.

A stellar black hole forms when the center of a very big star collapses after the star runs out of fuel. A star with roughly 20 to 25 or more times the Sun's mass can leave a black hole behind. Smaller stars end as white dwarfs or neutron stars. Black holes grow bigger when they take in more stuff from around them. They can also get bigger by crashing into stars and other black holes.

Black holes come in different sizes. The biggest are called supermassive black holes. Some black holes have as much mass as millions of Suns. Almost every large galaxy has a supermassive black hole at its center. Our Milky Way galaxy has a giant black hole at its center. It is called Sagittarius A*. It has about 4 million times the mass of the Sun.

The edge of a black hole is the event horizon. Nothing can come back out once it crosses it. The event horizon is not a hard surface like the ground. Gravity can be too strong to escape from. To leave Earth you need about 11 kilometers per second. Inside the event horizon you would need to go faster than light. At the center of a black hole there may be a point called the singularity. It is where everything that falls in ends up.

From far away, a black hole pulls on things the same as any other object with the same mass. If the Sun turned into a black hole of the same mass, Earth would not be swallowed. Something can orbit a black hole safely if it stays far enough away. Only things that get too close fall in.

The glowing disk of gas around a black hole is called the accretion disk. It is the main source of light we can see. Gas falling into supermassive black holes powers some of the most energetic things in the universe, including jets that launch particles to near light speed.

Black holes do not last forever. They very slowly shrink and evaporate.

Albert Einstein's ideas about gravity led scientists to predict that black holes can exist.

In 2019, scientists showed the first picture of a black hole. It was in a galaxy called Messier 87. The picture shows a bright ring with a dark spot in the middle. In 2022, scientists showed the first picture of the black hole at the center of our galaxy.

On September 14, 2015, detectors in Louisiana and Washington caught ripples in space from two black holes crashing together.

Words to know

• accretion: glowing gas disk
• singularity: center point
• orbit: travel around