What do you mean by galaxy evolution how do telescopic observations allow us to study galaxie evolution?

Answer 1

Galaxies can evolve into different forms depending on what type of gas, metals, stars, etc. are present, what the environment is around it, if it's accreting mass. This being said it is also difficult to observe the lifetime of something when it's life is on the order of giga-years. So we study what we can see optically, like merging galaxies, different shaped galaxies, young and old galaxies, etc. and try to remake them through simulations. These simulations help try and explain the missing matter problem (dark matter), black hole theory, or even just basic life history.