A black hole is not a hole. It's just stuff. A lot of stuff. It's more stuff than you can possibly imagine stuffed into a very tiny point. Stuff attracts other stuff, that's gravity, so a lot of stuff has a lot of gravity, even if it's in a tiny container.
Imagine a one ton elephant in a hydraulic press, crushed down to the size of a sugar cube. That sugar cube still weighs one ton, and contains all of the bits that used to make up that elephant, just really really really tightly packed together and you wouldn't want it in your coffee.
Now instead of an elephant, imagine our sun, pressed down to the size of a football stadium. It still weighs as much as the sun, and all of the planets still revolve around it at the same distance, so nobody's getting sucked in, but if anything came close to the edge of where the sun used to be, it's going to experience the same gravity as the sun used to give at that point.
This is the start of a "black hole"; it's just so much stuff that it has so much gravity that anything close to it is going to get pulled in and become part of it, but it doesn't look like it should have so much stuff in it because it's been crushed down to a tiny ball.
You could, if you could push it around like a Katamari, use a black hole to "suck up" (i.e. crush into a thin shell) the entire universe, but since you can't and since everything in the universe is so far apart from each other, it's only going to ever be able to "eat" what's very close by, as there's much much much much much much more space (i.e. not stuff) than stuff in the universe and it tends to move apart from each other.
there is no known limit to the amount of matter a black hole can consume.
However, there is a limit in how fast it can consume matter.
The gravitational attraction from black holes is really strong, and that strength can cause matter falling in to rub and squish and compress, heating it up. That hot matter will start to glow brighter and brighter the hotter it is.
Eventually, the stuff falling in will be so insanely bright that the outgoing radiation is stronger than the black hole’s gravity.
All nearby matter will get blasted away by the radiation temporarily, until it cools down again, and starts falling back in.
This actually leads to a fun physics problem we have yet to figure out. We’ve discovered supermassive black holes that are bigger than they should be allowed to be. If we assume they started as regular black holes, because of that “eating limit”, they haven’t had time to grow to their sizes just from consuming other matter. Figuring out where these come from is still an active field of physics research!
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