Question

What prevents a galaxy from disbanding?

Answer 1

Answer:

The mysterious Dark Matter matters in this expansion.

Explanation:

Like about 70'% water in human body, what matters most in our

universe is that about 70% of missing mass is Dark Matter (DM).

I am not sure that I am right. Yet, in my opinion, expansion when

water becomes steam is analogous to this transitory expansion,

from matter without atoms to its own expanded form...

Answer 2

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Gravity. All of the stars of a galaxy are all attracted to each other. This attraction is weak because the stars are very far apart, but it is enough to keep the galaxies together. There is also a large amount of matter that has never been seen (called "dark matter") that helps keep galaxies together.

This means Dark matter prevents a galaxy from disbanding.