How do black holes work? Are they three dimensional or two dimensional? How does a solid core of a star collapse into a void?

Question

I still can’t get my head around this one. Can anyone help? I know they’re hard even for famous physicists but if anyone can simplify this concept for me I’d so appreciate it! Thank you!

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Answer 1

Atoms are mostly empty space. Tiny protons and neutrons in the nucleus with tiny electrons going around. If you could remove all the empty space between the electrons and the nucleus the Earth would be the size of a tennis ball.

But gravity isn’t strong enough to remove all that space. The electromagnetic forces keeping electrons away from the nucleus they orbit is stronger than gravity. Even at the center of our sun, with all the weight of the entire solar mass pushing in from all sides, it’s still not enough to overcome the force keeping electrons away from the nucleus.

We’d still need more pressure.

There are some really big ass stars out there. Stars so big that all the weight crushing in from all sides actually is enough to overcome the electromagnetic force keeping the electrons away from the nucleus. Once a star reaches that size the atoms at its core collapse. Then the atoms next to them collapse, and so on.

All of the electrons and protons and neutrons are still there. The mass of the star hasn’t changed at all. It’s as heavy as it was before but it’s packed into a much, much tighter volume. A planet that was orbiting the star won’t be sucked into the black hole, it will continue to orbit it exactly like it had before because the weight hasn’t changed, just the size. It’s not like you see in the movies, consuming everything nearby. It’s not any “hungrier” now than it was before, it’s just that we’ve packed all that gravitational pull into a much smaller area.

Because the size is so much smaller the gravity is much more concentrated. *Gravity decreases proportionally with the square of the distance from the center of mass*. This means when you get twice as far away from the source of gravity you only weight a fourth as much. We can stand on the Earth just fine because we’re 8,000 miles away from the center of the Earth’s gravity. If you stood on a tennis ball sized Earth your head would feel weightless but your ankles would break from the strain.

If there’s enough gravity packed into a small enough area we get a black hole, a gravity so strong that anything that gets close enough to its pull can never escape. Not even light. Even photons, as small and as fast as they are, aren’t able to get away from a pull that strong.