Question: How do black holes form

Jonathan Mound answered on 18 Mar 2026:

Mass attracts other mass by gravity. So if you put a bunch of mass near another bunch of mass, it will all start to pull together and collapse down into a smaller region, getting more and more dense as it does.

If you have a “small” amount of mass that isn’t too tightly packed, then the mass can only get so dense. At some point the repelling forces between atoms will stop the collapse due to gravity.

However, ff you have enough mass close enough together, then the gravity is so strong that it overcomes the atomic forces and the mass keeps collapsing down to into a smaller and smaller region. At some point it becomes so dense and the gravity is so strong that nothing can escape the gravity of the object, not even light – that’s a black hole.

One way to make black holes is from big stars. During most of their life, the heat of the fusion in their core pushes out on the mass above the core and keeps the star from collapsing. However, at the end of their life the star “runs out of fuel” the fusion stops. Without that heat, the cores of the stars start to collapse down. If the star has enough mass, then the gravity will be strong enough for run-away collapse to a black hole.