I don’t really get how somthing that’s small makes it a black hole.
In: Physics
For very big stars, it is more that they become so dense and heavy they can’t stop from becoming tiny. The atoms can only push against each other so hard before they are pushed together, and as a star makes hydrogen into denser and denser elements the pressure passes that point and the atoms are mashed together. There are a few more points where an even smaller thing’s resistance to pushing stops it (like neutron stars, but that’s another story) but if you get past those eventually something happens that we don’t really understand yet and they condense to an infinitely small point along with a very very big explosion.
For things that aren’t stars, you could also crush them so hard that their particles can’t resist the pushing, but very big stars collapsing are the only natural phenomena we know where the pushing gets that intense.
Think about a trampoline. It sits mostly flat but can move up and down some.
If you lay flat on the trampoline you will change how the material sits and it will move downward, it won’t be by a lot, because your weight is spread out.
If you stand on the trampoline your weight is concentrated in one spot for the material moves even more, and you find yourself sinking down more, towards the ground. If someone put marbles onto the trampoline they would roll towards you
It’s the same with a black hole, which is basically a huge amount of mass concentrated into a very small point. This causes the ‘fabric’ of space to bend. But now instead of marbles it is planets, stars, and even light that ‘rolls’ into the bend in the fabric of space, and so everything gets smashed into the black hole, and the bend gets bigger and bigger. The more mass the black hole ‘catches’ the bigger it gets and the more it distorts the space around it.
Every atom has a certain amount if gravitational pull, very small but it adds up when atoms are in close proximity.
If all the atoms in an object are densly packed together, then they are all adding their gravitational pull to pull objects into a very small area. Sort of like a focused lens for gravity.
If all the atoms are spread out, then that same gravitational pull is spread out over a larger area, meaning that all the atoms are fighting with each other to pull the object closer to them, some of the forces end up cancelling out.
When things become so immensely packed with atoms they have a gravitational pull so large that not even light can escape. That’s a black hole.
In your example, shrinking something down would make the atoms more dense and focus the gravitational pull until it is able to pull in more atoms to create even more focused gravitational pull.
Gravitational force is proportionate to mass and inversely proportionate to distance from the center of gravity. The smaller an object is, the closer you can get to its center of gravity. So for a sufficiently small size to mass ratio, you can get close enough to the center of gravity that the gravitational force becomes too strong for light to escape, creating an event horizon (and thus, a black hole).
It’s all about mass. A black hole the MASS of the earth would have a DIAMETER about the same as a cherry or a small grape. Mass attracts all other mass via gravity. If there is enough mass in a small enough space, gravity can become stronger than all the nuclear forces (the things that keep atoms whole).
This is why stars with enough mass (3-5 times larger than our sun) are able to overcome all of the outward pressures produced by atoms and subatomic degeneracy pressures and crush it all down into a singularity.
So in other words the size is determined by how much matter is present, not the other way around.
To ELYN5…the SIZE of that black hole ( or its event horizon ) can be calculated by
> R = 2MG / c^2
R = the radius
M = all the mass
G = the gravitational constant (-6.67 x 10^-11 )
C = the speed of light
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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