Maximum mass of a black hole

[dcheme7373]

The question, "why didn't the emerging universe collapse into a black hole" has been answered in other forums. Though I am not sure I understand the reason. But it got me thinking. Is it particularly stupid to ponder whether a black hole has a maximum possible mass? Or rather a certain mass threshold for which exceeding it results in some other phenomena? I believe the current accepted assumption is that more mass will just create a larger black hole and theoretically if all the mass in the universe was in close proximity to a black hole then we would have a black hole equal in mass to the mass of the universe. But the last time all the mass in the universe was at one point it spread out and did not form a black hole. Any thoughts?

 

[phinds]

First, if the universe is infinite in extent then there is no such thing as "all the mass in the universe "

Second, I don't believe there is any known physics that limits the size of a black hole

 

[DaveC426913]

But the last time all the mass in the universe was at one point it spread out and did not form a black hole. Any thoughts?

The moments following the Big Bang were not static. The matter that expanded from a small volume did not do so ballistically - as if shot out of a cannon. Spacetime itself expanded and carried the matter with it. (That's grossly simplistic. )

The key point is that this epoch of expansion is not constrained by the speed of light . It's believed that the expansion happened much faster than the speed of light* (not that the speed of light had much meaning during this epoch of time). *according to Wiki - in less then 10^-32 seconds after the BB, its volume expanded by a factor of 10₇₈ - i.e. from a molecule-sized up to about 10.6 light years - in 1 / 100 trillion trillionth of a second.

So, even if the matter were gravitationally attracted to clump together, it could not have done so faster than the universe was expanding.

 

[PeroK]

The question, "why didn't the emerging universe collapse into a black hole" has been answered in other forums. Though I am not sure I understand the reason. But it got me thinking. Is it particularly stupid to ponder whether a black hole has a maximum possible mass? Or rather a certain mass threshold for which exceeding it results in some other phenomena? I believe the current accepted assumption is that more mass will just create a larger black hole and theoretically if all the mass in the universe was in close proximity to a black hole then we would have a black hole equal in mass to the mass of the universe. But the last time all the mass in the universe was at one point it spread out and did not form a black hole. Any thoughts?

The short answer is that a black hole forms when a star of at least the critical mass collapses. Note that the star is surrounded by a vacuum. The early universe was a (possibly infinite) region of almost uniform density. It wasn't surrounded by vacuum. These conditions are therefore very different. This question gets asks quite regularly. See here for a fuller answer:

https://www.physicsforums.com/threads/in-the-beginning-there-was-a-black-hole.984254/

 

[dcheme7373]

Thank you for your responses. I think I understand now

 

[DennisN]

Second, I don't believe there is any known physics that limits the size of a black hole

Neither do I.