Question

How do galaxies retain their form?

Answer 1

Hint: Spiral galaxies are a type of classification of galaxy. These galaxies are spiral in shape and hence they got their name spiral galaxy. Our milky way is also a type of spiral galaxy. In these types of galaxies there is a galactic core in the center of the galaxy and all the stars revolve around the galactic core with different speeds.

Complete answer:
If we assume most of the mass in a galaxy is concentrated at the center, then the outer regions should move slower than the inner regions, but so as for spiral arms to carry their shape, the outer regions must move faster instead. The kinds of beautifully distinct spirals you're probably thinking of are usually attributed to density undulatory theory.
It is one among the more successful models developed to clarify the origin of spiral arms in galaxies is the density wave model. It's particularly good in describing the formation of the spiral structure we see in grand design spirals.
In this model, spiral arms are regions of the thin disk that are denser than average, and move round the galaxy more slowly than the individual stars and interstellar material.
The second important piece of physics for understanding spiral structure is that the celebs and gas within the disk of the galaxy exert an appreciable gravitational attraction. That force helps maintain the spiral form against the tendency to wind up. Almost everyone agrees on this basic physics

Note:
The stars and interstellar material move much faster than the high-density region of the spiral arm, because the interstellar material moves into the region of high density, it's compressed which successively triggers star formation. These newly formed stars still orbit around the center of the galaxy similar to the interstellar matter from which they were formed. The most luminous of those new stars have very short lifetimes compared to the quantity of time it takes for them to orbit the galaxy. For this reason, they're only found in, or very near to the spiral arm within which they were formed.