if there is even just one blackhole, wouldnt it just keep on consuming matter and eventually consume everything?
In: Planetary Science
Wow a lot of these answers are just… Not correct. They’re right about black holes not being gravitationally special, but still, the idea that gravity would pull the entire universe together into larger and larger black holes until everything was condensed down to a single point, that was an early theory for the end of the universe. It’s called the “Big Crunch”.
The real reason we don’t currently think that’s going to happen is… Dark Energy.
There’s a force in space which is pushing everything apart, and at large distances it’s stronger than gravity. This force is poorly understood, but the end result is the universe is actually expanding *faster* than it used to, it’s not slowing down due to gravity.
If the Sun turned into a black hole right now, the force of gravity with which it is pulling the Earth towards itself would remain the same.
Gravity pulls you towards the center of mass of the object you are being pulled towards.
How hard gravity pulls on you depends on how heavy the other object is and how close you are to its center of mass.
Black holes dont pull any harder per how much they weigh than regular stars.
But you are limited in how close you can get to the center of mass of a star because of how big the star is. You will hit the surface of the star while you are still a hundreds of thousands of miles away from the center of the star.
Black holes are small, which allows you to be much closer to the center of mass of something as heavy as a star. The mass of the star is the same but it got squished into such a small ball that you are only 20 or so miles away from its center of mass when you touch the surface.
Not only will Black holes not just grow and grow. They will eventually evaporate:
https://www.scientificamerican.com/article/this-is-the-way-the-universe-ends-by-evaporating/#:~:text=In%20this%20way%2C%20black%20holes,them%2C%20causing%20them%20to%20evaporate.
Spread a bunch of marbles out across you mattress.
Set a large, heavy stone (a black hole) down on one spot of the mattress. You’ll likely see many of the neighboring marbles fall to the point your finger is at.
Then marbles increase the weight near the stone and may draw some number of additional marbles into the spot. Would they pull every marble in from the entire mattress, though? If not, why not?
Like others said, black holes don’t actively drag things in, they’re no more dangerous than a star of the same mass. But for the sake of argument, let’s suppose they *were* as ravenous as popularly believed.
Even if it *did* just keep on consuming, there’s a limit to how fast black holes can eat. Try to stuff too much matter into it at once and it starts getting bumped out of the accretion disk before it can fall in.
Even if it *did* just keep growing, empty space has a whole lot of… well… empty space. If it consumed an entire galaxy, there wouldn’t be anything else unless there were others close enough by to be affected by its gravity.
Even if it *did* consume an entire *cluster* of galaxies, it would take so long that the expansion of space would certainly cut off its supply after that.
Imagine you’re in your room and you need to vacuum. The vacuum is going to suck in all of the things within a certain distance. Things beyond the suction of the vacuum won’t get sucked in.
The universe is gigantic – like its unprocessable how big it is. If the universe was the size of the earth, even the biggest black holes would be the equivalent of a vacuum cleaner.
The question you asked is kinda like asking, why aren’t all these vacuum cleaners destroying the earth.
If there was a black hole as massive as the sun at the center of our solar system, the earth would continue to orbit exactly like it is today.
They have the equivalent mass as regular objects, so their gravitational pull is exactly the same. They aren’t huge vacuum cleaners that grow indefinitely.
The main difference is what happens to matter once it gets really close to the black hole.
Gravity is gravity is gravity. Are you a gigantic super red giant star? Do you have something orbiting you 0.5 light years away because you big massive star? Great, let’s shrink you star down to a pin head. You got the same mass so you got the same gravity! But, if light get close to you, it get sucked in. Only if it get super close though. That thing out 0.5 light years out? It don’t know difference because you still same mass, same gravity. But now your gravity is super concentrated and there’s an area around you with super suck. But it’s small. The boundary of that area is called the “event horizon”.
One day when you find another black hole you fall in love with, you can merge together. And then later you can merge together with more black holes in a weird polyamorous way like they do in California. Then you become a Super Massive Black Hole, and you can have whole galaxy orbit you!
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