Answerer

Guys, how large can a black hole get?

fando

I don't think there's a known upper limit to the mass of a black hole. The largest ones are speculated to be billions of solar masses and reside at the center of large galaxies like our own.

Defiant Heretic

I'm fairly certain that's been confirmed.

[Edited to add: ]
Here's a <a href="http://www.msnbc.com/news/135107.asp" target="_blank">link</a> to some info about it.

[ November 23, 2002: Message edited by: Defiant Heretic ]</p>

crocodile deathroll

Here is a <a href="http://www.cnn.com/2002/TECH/space/11/22/runaway.blackhole/index.html" target="_blank"> black hole heading our way </a>. But shucks, it is going to miss us by 1000 light years.

Answerer

I feel that there is an upper and lower limits for most, if not all, of the phenomenons in science. I do recall hearing(or see) the fact that black holes may get unstable if it get too large.

fando

I agree. Are you familiar with the concept of <a href="http://www.santafe.edu/~vince/emergence_alife/emergence_alife.html" target="_blank">emergent phenomenon</a>? If so, then I think that the limit doesn't matter in this case because the upper bound of the phenomenon of General Relativity is ridiculously large. If not, then ignore what I just wrote and read on.

It could be that there is such a point. But what merit does this speculation have? I am somewhat familiar with the particulars of General Relativity, our best model of spacetime on the macroscopic level, and there's nothing in it to my knowledge that puts a limit to the size of a black hole up until it starts affecting the isomorphism and homogeneity principles. I am guessing that the upper bound on mass due to this is ridiculously large, on the order of galaxy masses. After that, General Relativity is insufficient to describe the black hole, but that doesn't mean that a black hole can't be larger.

Ahh, it's all speculation. But it's fun!

Primordial Groove

Is it possible that black holes will keep engulfing matter, thus, reversing the expansion of the universe? If black holes were able to get galaxy sized+, it seems the gravitational pull would be strong enough to affect large distances.
Could this be how the big bang started?
A black hole, gets bigger and stronger, sucking all matter, then, due to 'something', the singularity starts the big bang all over again?

Shake

I believe the currently accepted theory is that there just isn't enough matter to make the universe collapse back in upon itself. I'm sorry that I can't give a source for this, it's just something I remember reading.

Also, on the point of black holes getting indefinitely bigger and more powerful, Professor Hawking has shown a way for black holes to "evaporate" due to the release of virtual particles near the event horizon. The theory goes that there are constantly virtual particles with their antiparticles being created and a very, very, very short time later annihilating each other. When this sort of thing happens in the vicinity of a black holes' event horizon, it is possible that one of the particles will get sucked in and the other will be free! You can probably find more about this in some of Hawkings' writings.

Answerer

But Shake, I always thought that virtual particle concept is only a theory and it has never been proved(experimentally) or widely-accepted among the experimental physicists. So, how do we know it really reflected the real situation of a black hole?

<img src="confused.gif" border="0">

Shadowy Man

Answerer:

Look up "Lamb shift".