Black holes are objects in space.
They form during supernova explosions. These happen when very massive stars reach the end of their lives. After a supernova, any remaining material is squeezed into an extremely small and dense object. This object is a black hole.
After a black hole forms, it can grow. It pulls in gas, dust, stars, and other black holes. Black holes formed in this way are called stellar-mass black holes.
Over time, much larger black holes can develop. These are called supermassive black holes. Supermassive black holes are millions of times more massive than stellar-mass black holes. We are still uncertain how they form.
Most large galaxies have a supermassive black hole at their centre.
In 2015, gravitational waves were detected. These ripples are changes in space-time. They were caused by two black holes colliding. This released a lot of energy.
Near a black hole, its gravity is strong. Nothing can escape from this region. Not even light. They do not emit or reflect light.
The boundary where light can no longer escape is called the event horizon.
In 2019, astronomers produces an image of a black hole’s event horizon in the centre of the galaxy Messier 87.
We can observe the effects of black holes. The gravity of a black hole pulls strongly on nearby stars and clouds of gas and dust. As this material falls inward, it swirls around the black hole. The collisions between particles create heat and light.
This light forms far enough from the black hole that it can escape and be detected.
Black holes can be found using gravitational lensing.
Their strong gravity bends light from distant galaxies. This can stretch the light into rings or create multiple images of the same object.