Question: What happens to stuff that gets sucked into black holes after its been compressed so much it wont get smaller.

Sam Connolly answered on 17 Jun 2014:

Good question, but no one knows for sure! We can’t see inside black holes, because light can’t escape them, so we have no direct evidence of what’s happening inside. There are theories though, of course. A lot of people think all of the stuff in the entire black holes is squashed into a tiny point in the very centre, called a ‘singularity’, which is incredibly, or even infinitely dense. In that case the rest of the black hole would be empty! (The surface of the black hole, or ‘event horizon’ is then the distance from this point where gravity gets too strong for light, or anything else, to escape). Others think that all the stuff is actually piled up just behind the surface, with the middle empty, like a beach ball or balloon.

The weirdest theory that people have suggested about the stuff inside a black hole is that it turns into something called a ‘quark-gluon plasma’. Quarks are the smallest particles known and make up sub-atomic particles like protons and neutrons, which in turn make up atoms. Gluons are a special type of particle similar to photons (which make up light). And a plasma is a state of matter, similar to a gas, which you get when something is really hot and squashed up. Normally, quarks always come in sets of two or three, to form bigger particles, but some people think that inside a black hole they could exist on their own, as this special kind of plasma. But we really don’t for certain yet, which is why we’re still studying black holes!