What is a black hole?

A black hole is a place in space where gravity is so strong that nothing can escape — not even light. That is why it looks black: no light comes out for us to see.

Most black holes are born when a giant star runs out of fuel and collapses. All its material crushes into a tiny point, and the pull around that point becomes overwhelming.

The edge of a black hole is called the event horizon. Cross it and there is no way back. Outside it, however, things are normal; the Earth could orbit a black hole safely from a distance, just as it orbits the Sun.

There is a huge black hole at the centre of our own galaxy, four million times heavier than the Sun. In 2019, scientists photographed a black hole for the first time — or rather, its shadow against the glowing gas around it.