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What would happen if you stopped a galaxies rotation? Answered

I mean a total complete standstill, every dust particle and bit of matter stopped moving rotationally in relation to the galactic center. Would the gravitational effects drag everything to the center if it stopped rotating over a few million years or would everything fly off in a straight line if it stopped instantaneously and eventually fall back into the center? 


Interesting article, "Black holes die, but it takes a while".

The Black Eye Galaxy has clouds which spin counter clockwise to the core, as a result of a past merger. If it ever developed collimated jets, I would think the black hole would be drained and the galaxy would stop rotating eventually.

The Universe is forming orthogonal structures and voids. These are apparent in a map called 'The Universe within 200 million light years"(atlasoftheuniverse.com/200mill.html)”

There are no threats above and below our Local Sheet due to the voids which have developed. Looks like we're sandwiched in between several walls, which exert a pull on us from every direction, which keeps us anchored. M87 is like a wood chipper with galaxies on a conveyor belt feeding it. M87 is a giant recycling machine, spewing out synchrotron radiation as it recycles galaxies.

Might a black hole function like a dynamo, powering the galaxy?

Thank God M87 has such a powerful attractive force to hold onto thousands of galaxies otherwise we'd be obliterated.

And, we're lucky that we don't have as many globular clusters as M87. Our Milky Way Galaxy has about 180 globular clusters; Andromeda has about 460 globular clusters and Triangulum has between 52 to 122. All told, the 3 largest galaxies in our local group have < 800 gcs compared to M87, which has about 13,000 globular clusters.

M87 is a place "of unimaginable violence" according to Stardates' Black Hole Encyclopedia . It is said to contain a SMBH of 6 billion solar masses.”


7 years ago

It would mean the end of the universe.

If it ever happened, every thing will fall into the middle of the galaxy


7 years ago

Seriously, you would ultimately create the Biggest of all BLACK HOLE !!

But in the thousands of years while your magic rash act worked toward it's
conclusion some race of beings would find a way to stop your action from taking place.


Just had a second.... actually fifth thought.
You didn't say stopped and released though you implied it.
If your magic stop, stopped, it would stay where it  was/is  like a special
effect movie end of story.

If your stop was based on halting and deleting inertia then releasing matter
from the magic grip ( important, How Long was your grip ).
Think what a star like the sun would do next ??!!
Or can you leave stars and black holes untouched ?

Magic is used to describe a process that technology cannot explain now !

Yeah. Can't happen; so the real answer is "mu". But for the sake of argument, I figured I'd give him an answer and a pointer to how such answers are determined.

I'm not saying it can't happen. It's just that angular momentum has to be conserved. Pulling a large spinning mass into itself makes the whole thing spin faster. The usual textbook example is that of a figure skater who spins faster when she pulls her arms and legs in towards her center of rotation. 

For objects much, much, larger than figure skaters , the fast spinning center leads to funny stuff like accretion discs and relatavistic jets.


What have you got against galaxies? (leave them alone...)


If everything stopped moving around the galactic center, it would have no momentum. The only remaining force would be gravity. Hence, everything would fall inward.

If you somehow turned off gravity instead, everything would fly off in straight lines, and wouldn't have any reason to fall back unless you re-established gravity... at which point it would fall into new orbits.

The equations of motion, in discrete-approximation form, aren't very complicated. If you're really interested in this, it wouldn't be too hard to code up some computer models. Though those two thought experiments are a lot simpler and less interesting than those involved in more realistic problems like determining how a research probe can be gotten to a specific point in the solar system in a reasonable amount of time with minimum expenditure of rocket fuel (websearch "gravitational slingshot") or trying to predict a comet's future path.

It's all basically F=MA, inverse square law for gravitation, and cumulative effects over time.

As far as how long the collapse would take: The numbers are notoriously fuzzy. "Space is big. Really, really big." And inverse square law means there really isn't that much inward force, on that scale. On the other side, as mass accumulates toward the center it would distort space-time, eventually becoming a very large radius black hole... and I think all our theories give up before they give us a good answer to a hole that large.

But: The galactic radius is approximated as 50,000 light years. That's 50,000 years if everything was already falling inward at lightspeed -- but it's starting out at rest, in your experiment, so it has to build up toward that speed over time, from a very weak force acting on some very large masses (the solar system is on the order of 1.98E30 kilograms). The current inward gravitational force can be back-calculated from the facts that we're about halfway out the radius, and we orbit the galaxy in about 220-250 million years... though figuring out whether and how that force changes as everything falls inward might be complicated.

After that it's all integration and, as the speeds start to be a noticable fraction of C, relativity.

Good question to ask a physics teacher to help you solve, if you're looking for an extra credit project.


7 years ago

All of the matter in the galaxy eventually, over millions, maybe billions of years, would be sucked into the black hole at the center of the galaxy.
Then you would have a black hole of monstrous size moving around gobbling up more galaxies and merging with other black holes. Eventually, the entire universe would return to the singularity.
After that, your guess is as good as anyone else's.

If you magically stopped all the rotation, then, yes, he whole thing would collapse under its own gravity.

However, the collapse would probably take thousands, maybe tens of thousands of years - galaxies are big.

and inadvertently would have a little collision here and there...likely causing an offset of mass from the center of gravity compared to the center of mass...and likely induce rotation again :D