What is a black hole?
A black hole is a region of space where gravity is so strong that nothing, not even light, can escape. Most form when very massive stars collapse at the end of their lives.
When a star much bigger than the Sun runs out of fuel, its core can collapse under its own gravity. If enough mass is squeezed into a small enough space, it forms a black hole. The boundary around it, beyond which nothing can return, is called the event horizon.
Supermassive black holes, millions or billions of times the Sun's mass, sit at the centers of most large galaxies, including our own Milky Way. Scientists detect black holes by watching how they affect nearby stars and gas and by the gravitational waves produced when black holes merge.
Seeing the invisible
In 2019, the Event Horizon Telescope released the first image of a black hole, in the galaxy M87, showing a glowing ring of gas around a dark shadow. In 2022 it released an image of Sagittarius A*, the black hole at the center of the Milky Way.
Did You Know?
Black holes slowly lose energy through a process predicted by Stephen Hawking in 1974, called Hawking radiation, although it has not yet been observed.