Neil is just getting several different facts confused, all of which are right but not together
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Almost every galaxy seems to have a central black hole, or end up with one eventually. These are, as MW said, extremely massive. Much light - stellar mass - black holes are very common (all very massive stars end up that way), but they're scattered throughout the galaxies. A galaxy with more than one central black hole wouldn't last very long, the gravitational tug of war would cause the two to merge
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In fact, after large galaxies (each with their own central black holes) collide, this is what's believed to happen: the two black holes migrate to the centers of their respective galaxies, and then soon merge.
As for fallingstar's original question, I'm not entirely sure. In fact, neither are the pros
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Black holes play a crucial role in galactic formation, but I'm not 100% sure what the prevailing theories on that are. As for some specific questions...
Fallingstar1971":29zpz1sq said:
Could a galaxy form from just a spinning mass of gas, or is a black hole required?
The first galaxies definitely form without a supermassive black hole - there's just no way to build black holes THAT big before galaxies form. Galaxies first form from collapsing gas; the black hole is not a required component. The black hole is, however, important in the subsequent growth of the galaxy, mostly as a way of providing energy, rather than, as you suggest, for the fact that it's really big. In fact, though these central black holes are huge, they're still about 1/1000-1/10000 the mass of the host galaxy, so they aren't hugely important in keeping the galaxy together - the self-gravitation of the galaxy is more than sufficient.
Have any galaxies been found with no central black hole?
Believe so, yes.
Could it be faked by forming a galaxy from a spinning cloud with no black hole? Stars would still appear to orbit the center even though there would be no object to orbit. There motion would be due to the cloud spinning when the galaxy formed. Since black holes are not directly observable, Im thinking that it could be possible, all the "quiet" (non-active) black holes may not even exist. What other tests could be used to detect a non-active black hole?
See the above - the black hole in the center isn't exactly what the stars orbit. Stars on the outside are pulled in by the interior stars, and so on. Think about it like the Sun, which is also held together gravitationally, even though the particles in the Sun don't orbit around some central object.