How do galaxies retain their form?
1 Answer
We're not 100% sure yet...
Explanation:
How galaxies keep their form is a mysterious thing. Simulations show that the matter in a galaxy simply isn't enough to hold it together. There is something else at play here.
One possibility is supermassive black holes. We have found very large black holes (anywhere from 1000 to 1000000 solar masses) in the center of most galaxies (including our own).
These black holes explain the bulge in the center of many spiral and elliptical galaxies. But they aren't enough to hold a galaxy together.
The most accepted explanation is dark matter. Dark matter is nearly undectable and as such very unknown to us.
We know it exists due to how light is bent around galaxies due to gravitational lensing. Adding the factor of dark matter to our simulations allows galaxies to stay together, due to dark matter's unusually strong gravity.
Dark matter, as far as we know, makes up about 23% of all the "stuff" in the universe, yet we have no idea what it actually is.
Sorry for the long explanation, but this question still doesn't have a concrete answer.
