Black holes are not empty

A black hole sounds like an empty hole in space, and it looks empty and black because it
 gives out no light. However, it is in fact an area where gravity is so strong that nothing, not even light, can escape from it.

At the end of its life, a giant star collapses and shrinks. Its mass gets more and more compressed until it is so thick that light can’t escape from it because so much material has been crammed into a small space. If you take a sponge in your hands and squeeze, you make it smaller but it still has the same mass. However, when an object is made smaller in that way, its gravity becomes much stronger. A black hole’s gravity is so strong that not only can nothing escape, but anything that gets too close is pulled in!

Gas and dust that are sucked into a black hole do not dive straight in, but move in an orbit around it as they slowly spiral inwards. The friction of the gravitational pull of the black hole heats the material to incredibly high temperatures, which makes its orbit around the black hole shine brightly. By looking at the brightly lit orbits around the outside of the black hole, scientists can estimate its size.

Gas and dust pulled towards a black hole, heat up and shine brightly as they spiral around the black hole. This is how scientists can tell where there is a black hole. © Getty Images

Gas and dust pulled towards a black hole, heat up and shine brightly as they spiral around the black hole. This is how scientists can tell where there is a black hole. © Getty Images

How big are black holes?

The size of a black hole depends on how much material is in it. When huge stars, many times bigger than our Sun collapse, they become black holes that are just a few kilometres in diameter. However, some galaxies have at their centre, a black hole millions of kilometres in diameter.


Read about how black holes are found in space.

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