What state of matter is a black hole?

Question

Is it an absence of matter? Or what?

Answer 1

So far as we know, black holes can form either as remnants of very large stars after they run out of fusion material and collapse due to dominating gravity or as the result of a merging neutron star binary or other possibly other collisions. Black holes are matter concentrated so densely that there is a region around them at which the escape velocity of a nearby object would have to surpass the speed of light. The boundary of this region is called the event horizon and it is the black external surface of a black hole that we could see. Since no light can escape from within this boundary, black holes are perfect blackbodies (if we ignore small Hawking radiation) - objects that absorb light at all wavelengths and don't reflect or emit anything. It's hard to talk about what state of matter the matter inside the event horizon is since its impossible for us to see, but we do know that its incredibly dense and likely very cold - getting colder the more massive the black hole.