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I don't understand how the event horizon booms to be so large compared to it's mass. And does a black hole suddenly pop into existence when that density is reached, or does it need to collapse or have some condensed distribution?
A black hole is an object so dense and heavy, even light can't escape its gravity. Black holes appear when a star collapses and reaches the required density.
Yeah I get that. But the video was saying a black hole the diameter of the solar system has an average density inside the event horizon of air. I was wondering if you need to compress it any, or if a solar system sized volume of air would already be a black hole, or would it need to collapse to a singularity first?
Because math. Also, it's the average density.
It's probably some obvious volumetric thing, like how the volume of a sphere increases exponentially when you increase the radius. V = 4/3 πr³. It seems the mass is some radius analogue in whatever equation governs black holes.
It's also interesting to note that the surface area of a black hole's event horizon is proportional to how much inormation the black hole contains. This was discussed in a recent PBS Spacetime Video.
The thing is, you have to first create the black hole with the mass of the universe in order to be so large that it has the same average density as air, right? Maybe I'm totally wrong and need to watch the video.
If the volume of air is big enough, it will be so heavy that it will act as a black hole. It doesn't need to collapse first, although it probably will because of its own weight.