I don’t really get how somthing that’s small makes it a black hole.
In: Physics
Gravity follows the inverse square law. That is, the strength of the gravity is inversely proportional to the square of the distance. Move twice as far away and the strength is four times weaker. Go three times as far away and the strength is nine times weaker.
Matter takes up space. You’re standing on the Earth, and that puts you right next to the Earth. But you’re not right next to *all* of the Earth. You’re pretty dang far away from most of it, really. For sure, the gravity of the core and the far side of the Earth affect you, but not as much as they would if you were really close to it. Except, you *can’t* be close to it, because there’s all the rest of the Earth in the way. And, of course, if you tried to get closer, you would then be moving through the Earth and getting farther away from *this* side of the planet. Once you were inside the planet, the gravity of the stuff above you will also be pulling you, somewhat canceling out the pull of gravity from the other side.
That puts a limit on how strong gravity can be at any single point. Even if there’s a lot of *stuff*, that very stuff gets in the way and keeps you far away from other stuff. Inverse square law reduces the force of gravity that you feel from all the matter that’s on the other side of whatever is creating the gravity.
You may already see what makes a black hole different. If you squeeze all that stuff down, it means you can get *really* close, even though there’s a *lot* of stuff. Far away from the black hole, gravity isn’t different. If you magically replaced the Sun with a black hole of equal mass, the Earth would keep orbiting as if nothing had changed. It’s only when you get close that it matters – because normally you *can’t* get that close at all, if it were an object made of normal matter.
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