It doesn't seem like there's a limit to how big they can get just a limit to how quickly they can get bigger due to what's called the Eddington Limit which explains how matter falling into the black hole emits radiation and if enough radiation around the accretion disk builds up, it can overcome the pull of the black hole and push matter away, at least until enough matter is pushed away that the radiation levels fall back under the limit and matter starts falling in again.
PBS Spacetime had an episode somewhat recently about a black hole which is growing at many (hundreds? thousands? I forget) times the Eddington Limit. And, as far as I remember, it isn't the only one to exceed the Eddington Limit - just the one with the record for how much it exceeded it.
I'll try to dig it up when I'm not at work (or if I remember the exact episode through the day).
Importantly, the Eddington limit does not apply to black hole mergers, theoretically allowing as much growth rate as you're able to feed in from smaller black holes.
This said, the final parsec problem isn't solved/understood. We know black holes do merge, but we don't understand what energy is being bled out of the system so supermassive black holes crash into each other in the timeframes we're seeing it occur.
So then the only theoretical limit on black hole mass would just be how fast you can put matter in black holes and/or merge existing black holes versus how fast the universe expands?
I'm 100% an armchair physician so take my words with a grain of salt but it seems like according to the math there is no limit to how massive a black hole can get. There are limits on the size of how big and small things can get and how hot or cold they can get, the second part is pretty cool, Physics Explained on yt has a good video on it (he's got a lot of good videos) but I enjoyed this one on what the maximum temperature is in the universe: https://www.youtube.com/watch?v=NVlEQlz6n1k
I heard a joke about a nerd who dies and finds himself in a very hot underground cavern. The devil is there, and says "Welcome to Hell! This over here is the lake of molten lava where you'll spend the rest of eternity". The nerd says "well actually, since it's underground it's called magma rather than lava". The devil replies, "um, you do understand why you're here, don't you?".
I try to remember that when I'm tempted to point out mistakes that are fine to overlook.
> [270B solar masses] is the maximum mass of a black hole that models predict, at least for luminous accreting SMBHs.
as well as:
> The limit is only 5×10^10 M [50B solar masses] for black holes with typical properties, but can reach 2.7×10^11 M [270B solar masses] at maximal prograde spin (a = 1).
However in the chapter before, it's stated:
> New discoveries suggest that many black holes, dubbed 'stupendously large', may exceed 100 billion or even 1 trillion M.
If you assume constant density, anything becomes a black hole at certain volume. The question is: is our universe big enough to be a black hole or not.
I know this article. It's citing a bunch of speculative hypothesis by mostly this one person which relies on something super exotic called Einstein Cartan theory. I stand by my statement. I even suspect the article was written by them.
You have elsewhere in this thread objected to people providing links without giving context, so I hope you won't mind being asked to unpack this claim a little. Why is it nonsense? If, as you say, it's principally pushed by one person, who is that, and why does that argue against it?
(I'm not thinking this is too much to ask; saying it's wrong might require empirical support, but the claim that it's "nonsense" should be easier to justify.)
First of all, black holes have an interior and an exterior. Our universe only has an interior. Next, black holes have a singularity into which everything vanishes, or at least moves towards. Im our universe, everything moves away from a singularity. So if anything, it resembles a white hole more than a black hole. Also, our universe is expanding, whereas black holes shrink (unless matter falls into them, which can't happen to our universe because it has no exterior).
The interior and exterior are isolated; we have no idea if are universe has an exterior or not and, according to present theory, never will.
As another comment pointed out, in GR our "future" is a singularity which everything moves towards (so what we see as a time dimension).
"Expanding" and "contracting" depend on your coordinate system. If your rulers are shrinking, you can't tell this from space expanding.
The common factor here is you are wanting to use our reference frame (somewhere in this universe, not near a black hole) to describe things as they would be seen from other reference frames.
I love to contemplate galactic-scale synchrotrons that accelerate supermassive charged black holes to collide at relativistic speeds. The thought never really goes anywhere, but I'm sure it'd be a spectacle to behold.
It would be just about the only way we could get the data required to resolve the contradictions between the Standard Model and general relativity. The unification energy is simply stupendous.
Poking around those articles (and knowing nothing really), it is interesting to note a couple references to a 50B solar-mass limit for “luminous accreting black holes hosted by disc galaxies.” (In your Phoenix cluster link). I guess these ones are easier to spot, based entirely on the word “luminous.”
There are other larger ones out there, looming in the darkness.
Yes - but it's basically the same as the total mass of the universe.
EDIT: I believe the above could be incorrect - if the universe has too much electrical charge or angular momentum. (And some other cosmological properties, so you couldn't get around the charge & spin issues.)
Might there be a black hole astrophysicist in the house, to comment on this?
