A black hole is a region of a spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The strong gravity occurs because the matter has been pressed into a tiny space. This compression can take place at the end of a star’s life. Some black holes are a result of dying stars.
Because no light can escape, black holes are invisible. However, space telescopes with special instruments can help find black holes. They can observe the behavior of material and stars that are very close to black holes.
When a black hole and a star are orbiting close together, high-energy light is produced. Scientific instruments can see this high-energy light.
A black hole’s gravity can sometimes be strong enough to pull off the outer gases of the star and grow a disk around itself called the accretion disk. As gas from the accretion disk spirals into the black hole, the gas heats to very high temperatures and releases X-ray light in all directions. NASA telescopes measure the X-ray light. Astronomers use this information to learn more about the properties of a black hole.