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. The edge of a black hole is called the event horizon. Nothing can come back out once it crosses the event horizon. The event horizon is not a hard surface like the ground. Black holes are invisible, because no light comes out of them. Black holes can spin.

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 when it runs out of fuel. Smaller stars end as white dwarfs or neutron stars. Black holes come in different sizes. The biggest black holes 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. The black hole in the middle of the Milky Way, called Sagittarius A*, has about 4 million times the mass of the Sun. Scientists are not sure how supermassive black holes form. They may grow by merging with other black holes and swallowing stars.

Space telescopes can help find black holes, even though we cannot see the black holes themselves. We find black holes by looking at what they do to the light and stuff around them. Gas that falls toward a black hole gets very hot and glows, so we can see the glow even though we cannot see the black hole. The strong gravity of a black hole can bend light from things behind it. 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, in a galaxy called Messier 87. The first picture of a black hole 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. As of November 2026, the shadow of the black hole in galaxy M87 is about 38 billion kilometers across. As of November 2026, the black hole has a mass of roughly 6.5 billion Suns.

On September 14, 2015, detectors in Louisiana and Washington caught ripples in space from two black holes crashing together. The 2015 LIGO detection was the first time scientists ever caught two black holes merging. It was a collision that had been predicted but never observed. The first black hole merger ever detected happened about 1.3 billion years ago, roughly a billion light-years away.

Black holes do not roam around space eating stars and planets. 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.

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

Words to know

• horizon: edge
• supermassive: very big
• merging: joining together
• evaporate: slowly vanish
• gravity: pulling force