Maximum Size for a Galaxy

persiaprince

Is there a known limit set by the laws of our universe that limits the size of a galaxy?

Basically my friend and I were having an argument over a theoretical universe that was governed by the same laws as our own. I said that in this universe there is a galaxy that is 1/4 of the universe or perhaps just one that has 1/4 of the mass. My friend disagrees that this is possible. Can anyone shed some light on our debate?

culinaryoverlord

persiaprince wrote: »

Is there a known limit set by the laws of our universe that limits the size of a galaxy?

Basically my friend and I were having an argument over a theoretical universe that was governed by the same laws as our own. I said that in this universe there is a galaxy that is 1/4 of the universe or perhaps just one that has 1/4 of the mass. My friend disagrees that this is possible. Can anyone shed some light on our debate?

Hmm, when you look at the way the universe was created, I don't think God would intend for something that large to exist.

Heh, heh, just kidding.
Given a random, but somewhat "clumpy" distribution of matter at the beginning of your hypothetical universe, it would take some pretty rare odds for 1/4 of it to be so close together that it formed a coherent Galaxy. Things would be drawn together, but a lot of the matter drawn in would have sufficient velocity to be thrown out again because of the massive gravity, most likely as hardcore radiation like X rays and Gamma rays. The center would be so full of massive black holes it would be the "jersey shore" of the cosmos.
There are, I think, "Supergalaxies", in our universe, ones much larger than our own, and also Galactic clusters. But ones much larger than that are unlikely in a universe with the same physics. Fuck with gravity and a few other forces a little, and it might work. But our universe ended up the way it is because of the laws inherent to it's creation, to start a universe under the same conditions would, I think, guarantee the same result.

C/O
"Stephen Hawking could buttrape me anyday!!"

StephenPBarrett

^this. Keep in mind that what determines the size of a galaxy is the size of the supermassive blackhole in its center. Like C/O said, there would probably have to be several of these but unless they orbited one another perfectly they would eventually consume one another thus destabilizing the galaxy. All galaxies end somehow and that would be the most likely outcome of yours. IRL our galaxy is going to crash into Andromeda.

Oh and to answer your question you'd have to find out how big the largest supermassive blackhole is.

persiaprince

Thanks for the responses, but I'm not ready to give up on the idea yet and here are two of the things that are still on my mind.

1. In the first couple billion years of the galaxy all matter was confined to a smaller area of the endless universe(as far as I know). Because matter was much closer then shouldn't there have been fewer but bigger galaxies. Granted of course that there would be many less stars and planets.

2. There is a theory out there that seems to be gathering more support. I forgot what it was called but it called for a universe that refreshed itself with big bangs. It said that the black holes would eventually consume all matter and later, each other. When then all matter is consumed there would finally be another big bang. If my memory somehow managed to recite the theory right then wouldn't the universe at some point have very few galaxies, of super massive size that will eventually get consumed in turn?

Katzenklavier

Technically most of the galaxies we know of now are actually too small to be galaxies: the gravity math doesn't make sense. It's the dark matter that holds it all together, and in fact the milky way is 90% dark matter.

culinaryoverlord

Katzenklavier wrote: »

Technically most of the galaxies we know of now are actually too small to be galaxies: the gravity math doesn't make sense. It's the dark matter that holds it all together, and in fact the milky way is 90% dark matter.

I am reading " The Cosmic Landscape; String Theory and The Illusion Of Intelligent Design" by Leonard Susskind right now, a very well written book that provides a pretty good basis of knowledge about things like black holes, dark matter, dark energy, and quantum physics. I would recommend it to anyone. Quantum physics for dummies is also very good, once I recovered from the initial annoyance at being given a "for dummies" book for Christmas.

The relevance to the thread is that in order to understand why massive galaxies couldn't exist, you need to know why our universe has the characteristics it does. Our universe is one of limitless potential universes, some of which may include supermassive galaxies. But the cosmological constant, an expression of the dark matter/energy that is causing our universe to expand at an increasing rate, while also allowing the presence of structures like galaxies, would have to be different. So NIMBY to supermassive galaxies here. Could they exist in other universes?, sure, why not?

C/O
"Everything I learn now pushes something else out of my head, the aforementioned book removed about half of 1983"

Yay! Post 1000!

DARKCOLD

THE WHITE CIRCLE.
ITS COLD WITHOUT THE SUN IT WILL DROP DOWN TO ZERO
AND THEN IT FREEZES.

Darth Beaver

Some ody mite this moron.

Traum

DARKCOLD wrote: »

THE WHITE CIRCLE.
ITS COLD WITHOUT THE SUN IT WILL DROP DOWN TO ZERO
AND THEN IT FREEZES.

What the hell does this even mean?! Up until this post I was highly intrigued by this thread as I am greatly interested in anything surrounding black holes and/or galaxy creation.