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. 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. Scientists do not know what is at the center of a black hole; the singularity may be real, or only a mathematical idea.

Long before Einstein, John Michell thought that a very heavy star might trap light, and he called these objects dark stars. Einstein's general theory of relativity (1915) is where black holes come from, and in 1916 the same theory predicted gravitational waves. 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, 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.

Space telescopes can help find black holes, even though we cannot see the black holes themselves. Most stellar-mass black holes we have found are paired with a normal star. The hot gas pulled from the star glows in X-rays and gives the black hole away. A black hole with no gas near it has no accretion disk, so it makes no light and is almost impossible to see directly. Most black holes are found by the glow of nearby gas. We find black holes by looking at what they do to the light and stuff around them.

In 2019 scientists showed the first picture of a black hole, in a galaxy called Messier 87. The bright ring in the picture of M87's black hole is light from hot gas that is bent around the black hole. The dark middle is its shadow. The 2022 picture of Sagittarius A* was the first visual confirmation that the dark object at the center of our galaxy is a black hole. As of November 2026, the shadow of the black hole in galaxy M87 is about 38 billion kilometers across, and the black hole has a mass of roughly 6.5 billion Suns.

Black holes do not roam around space eating stars and planets. Something can orbit a black hole safely if it stays far enough away; only things that get too close fall in.

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. Black holes grow bigger when they take in more stuff from around them.

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

Words to know

• singularity: center point
• gravitational: about gravity
• shadow: dark middle
• evaporate: slowly vanish
• merging: joining together