So, most of you all are probably (well, why wouldn't you be) familiar with The Magellanic Clouds, and hour they are Irregular type galaxies. You should also be aware that they both orbit the Milky Way, so they act sort of like moons to a planet. Since they (most likely) do not have a central Supermassive Black Hole, I wonder, out of all ridiculousness, what are the answer to these two questions?:

1) What would happen to the Small or Large Magellanic Clouds if a Black Hole (maybe 100 time bigger than the sun) passed though them?

2) What would happen if Sagittarius A* passed through either the Small or Large Magellanic clouds. If you are not aware of Sagittarius A*, it is the Supermassive Black Hole that lies at the center of the Milky Way.

  • $\begingroup$ Are you specifically asking if Sag. A* itself passed through the Magellanic Clouds, or just a black hole with similar mass? $\endgroup$ – user10106 Apr 16 '18 at 15:57
  • $\begingroup$ Any of those two is fine. Just pick one or do both! :) $\endgroup$ – Commander KJ Apr 16 '18 at 16:04

Black holes (even SMBs) are actually very small objects on an astronomical scale and in practical terms probably very little would happen.

There would be some perturbations of stellar orbits within the formation they were in, but unless there was a fairly close approach very little would happen and on the scale of the entire formation the changes would affect only a small number of objects and not the overall "shape".

To put this in perspective, Sag. A* has a mass of about 4,000,000 solar masses. Sounds big (is big :-) ).

But the Large Magellanic Cloud has a mass of about 10,000,000,000 solar masses (or about 2500 time larger than Sag. A*). The dominant gravitational field is still that associated with the LMC itself, not that of Sag A*.

I think a good analogy would be a bullet fired into a lake. Sure, it can cut a path through one isolated region and cause disturbance close to that path, but the bulk of the lake will be undisturbed apart from a slight ripple.

The Small Magellanic Cloud is still a pretty large mass at about 6,500,000,000 solar masses, so still roughly 1,400 times more massive than Sag. A*. Again, we're talking bullet in lake territory.

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    $\begingroup$ Nice answer. Of-course a 4 million solar mass black hole doesn't exist without a galaxy around it, so, in reality this couldn't happen, but otherwise, spot on. $\endgroup$ – userLTK Apr 17 '18 at 3:11
  • $\begingroup$ The largest supermassive black holes we know about are comparable in mass to the LMC, although safely located in the centre of large galaxies in the middle of large clusters. However if one of those were somehow to be ejected and pass through the LMC it could cause considerable disruption. $\endgroup$ – Steve Linton Apr 17 '18 at 16:05
  • $\begingroup$ 0 down vote userLTK: a 4M solar mass black hole could quite possibly be ejected from its galaxy if two of three galaxies were merging. Specifically if it formed a binary with a similar sized black hole which then encountered a much larger one, one could be absorbed, while the other was ejected fast enough to leave its host galaxy. $\endgroup$ – Steve Linton Apr 17 '18 at 16:07
  • $\begingroup$ @SteveLinton Do you have a source for the claim that such a two or three way galaxy merger could eject one or more SMBs ? Has someone done a simulation of this ? Thanks. $\endgroup$ – StephenG Apr 17 '18 at 19:12
  • $\begingroup$ It's well established for binary stars passing close to the smbh. I can't see why it shouldn't work the same way for two million solar mass black holes in case orbit passing by a billion solar mass hole. $\endgroup$ – Steve Linton Apr 17 '18 at 21:35

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