Black Hole

A black hole is a place in space where gravity pulls so strongly that nothing can escape, not even light. Because no light can come out, a black hole looks completely black. Black holes are invisible on their own. Scientists find them by watching how they pull on stars, gas, and light nearby.

The edge of a black hole is called the event horizon. Once anything crosses that edge, it cannot come back out. The center of a black hole is called the singularity. Scientists think all the matter is crushed there into a point too small to measure.

Black holes come in different sizes. A small one, called a stellar black hole, forms when a giant star runs out of fuel and collapses. Its outer layers blast away in a supernova, and the core crushes itself into a black hole. A stellar black hole can pack the mass of ten suns into a ball just a few miles wide.

Much bigger black holes sit at the centers of galaxies. These are called supermassive black holes. They can hold the mass of millions or even billions of suns. Our own Milky Way has one at its center, called Sagittarius A-star. It weighs about 4 million times as much as the Sun. Nobody is sure how supermassive black holes got so big so early in the universe's history. That is one of the biggest open questions in space science today.

Black holes bend time as well as space. Clocks near a black hole tick more slowly than clocks far away. This is not a trick. Albert Einstein worked out the math more than a hundred years ago, and experiments with very precise clocks have proven he was right.

For a long time, nobody had ever seen a black hole. That changed in 2019. A team of scientists linked telescopes from all over Earth to take the first picture of one. The black hole, at the center of a galaxy called M87, showed up as a dark circle surrounded by a bright ring of glowing gas. The ring of gas is wider than our whole solar system.

One big question is still unsolved. What actually happens inside a black hole? The math we use to describe gravity breaks down at the singularity. Some scientists think tiny wormholes or brand-new kinds of physics might be hidden in there. We may never be able to look inside one to find out.