For decades, space and ground telescopes have provided us with spectacular images of galaxies. These building blocks of the universe usually contain several million to over a trillion stars and can range in size from a few thousand to several hundred thousand light-years across. What we typically see in an image of a galaxy are the stars, gas and dust that constitute these sprawling systems.
Source:
https://phys.org/news/2021-02-technique-galaxies.html