Can black holes “eat” matter indefinitely or is there a limit? Do they ever have trouble absorbing large masses or is it always the same?
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A black hole is a hole in visible light, not an actual hole. It’s a ball of mass, like a planet or a star, so dense that it’s gravity doesn’t allow light to escape.
Added mass only makes it bigger.
These are excellent questions: first of all there is no meaningful limit on how large a black hole can be. There are some practical limits like: it can’t be any bigger than the amount of matter in its direct vicinity, but generally speaking they can be anywhere from the mass of a large star to the mass of multiple galaxies. (As a side note: Some really old black holes can be absolutely enormous because the universe used to be a lot more matter-dense)
But yes, they do definitely have some limitations regarding how much mass they can absorb at any given time: if the matter they’re absorbing is highly energetic for instance, compressing it down further and further, and giving it all the kinetic energy of falling down into a gravity well can cause some pretty epic (for lack of a better word) explosions. You can think of it as a sort of series of naturally ocurring multi-thousand ton hydrogen bombs, because that’s essentially what happens when a black hole eats stellar matter. Hydrogen and helium that are already at fusionable temperature and pressure, and then are put under many times more pressure and many times more temperature
Well this kind of detonation can often expell some of the matter the black hole was drawing in closer, so in practice, black holes only eat a certain percentage of a star’s mass, and ejects small amounts of it at extremely high velocity periodically.
This means there isn’t really a limit on how much a black hole can eat theoretically, but there is a limit on how quickly and efficiently they can do so.
Also black holes can merge which is its own cup of physics tea, but I am not qualified to discuss the details of this sort of interaction so I would recommend someone else, but I do know this kind of merger can release a LOT of energy, and that the merger is not 100% mass efficient (the two black holes don’t keep the entire sum of their two masses)
Yes, they can, so far as we know you gotta think of a black hole as a giant pile of dirt, rather than a hole. There is no limit to how big a pile of dirt can get. Only difference is that the pile get super compressed, supposedly down to an infinitely small point in space. They will just get more and more massive over time, and one theory is that is how the universe will “end”, with all matter and energy being absorbed into black holes.
The best way to think of a black hole *isnt* as an endless void that eats things. It’s more like a dark star – no light comes from it but it’s still just a big, heavy object in space. Its way more dense than a star so it can have much higher gravity than a star of the same size, but it’s still just a big ol’ hunk of space stuff.
So then think of how things work with our sun. It’s big, it’s got lots of gravity, but does it suck everything into it? Not really. At least not on time scales we’re used to. Things tend to get caught in orbits around it. The orbits can be fairly stable unless there’s something slowing us down.
Black holes work like that.
Do things fall into black holes? Sure. If the space around a black hole’s event horizon (the point where going past it results in not even light being able to escape the gravity) is particularly full of stuff that has gotten trapped in orbit, those things can collide with each other, lose some speed, and their new orbit can take them into the black hole.
Is there a limit of how much stuff can do that? Not really. Black holes can get really really big. Galaxies are groups of billions and billions of stars orbiting “Super Massive” black holes.
The limit is basically “how much ya got?” – how much stuff comes into range and ends up falling into it instead of orbiting it. Black holes can even merge with other black holes!
IANAAstronomer, Astrophysicist, or really anything with Astro in the name. I just watch a lot of Dr. Becky’s YouTube channel and she *loves* black holes.
This isnt gonna be a good ELI5 answer but I wanted to add some context to some of the other comments here on.
” Neutron stars are formed when a massive star runs out of fuel and collapses. The very central region of the star – the core – collapses, crushing together every proton and electron into a neutron. If the core of the collapsing star is between about 1 and 3 solar masses, these newly-created neutrons can stop the collapse, leaving behind a neutron star. (Stars with higher masses will continue to collapse into stellar-mass black holes.)
This collapse leaves behind the most dense object known – an object with the mass of a sun squished down to the size of a city. These stellar remnants measure about 20 kilometers (12.5 miles) across. One sugar cube of neutron star material would weigh about 1 trillion kilograms (or 1 billion tons) on Earth – about as much as a mountain.”
[Article](https://imagine.gsfc.nasa.gov/science/objects/neutron_stars1.html)
So basically all for the matter that gets caught in the gravity of a black hole or neutron star gets compressed by gravitational forces so intense that they cause the nuclear forces that rule the structure of atoms to collapse, leaving behind densely packed subatomic particles. Before if you blew up an atom to the size of a football field it would be mostly empty space. Atoms in a black hole or neutron star in the this scenario would have no empty space.
Follow up question: Is there a theoretical point at which the matter inside a black home spontaneously turns into energy — IE can an overfed black hole blow up and release its matter?
A black hole wouldn’t have trouble absorbing a large mass as the way that it absorbs is similar to how we eat.
The stuff is made smaller and smaller until it is easy to digest. In our case we chew our food, in the black holes case it will destroy the stuff down to an atomic level.
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A fairly good analogy is a drainage hole in a bath/sink/etc. It’s kinda like a black hole but in 2d not 3d. There’s no limit to how much can go through, but there’s a limit to how fast stuff can go through.
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