Hubble image NASA APOD
Astronomers, astrophysicists, cosmologists and other scientists used advanced mathematics with theories of gravity, time, matter and space to figure out more about different types of galaxies. Much of the work was and continues to be theoretical with assumptions made on the basis of known laws of Nature.
Hubble telescope has the optics and ideal environment to provide needle sharp images of galaxies. But also Earth bound telescopes can today achieve images like this edge on picture of NGC 891 which is a combination of several photos.
It must be very satisfying - or challenging - to see with own eyes something that has only been rather abstract results of complex mathematical formula.
Adam Block from Mt. Lemmon Sky Center of the University of Arizona has thus provided visual evidence about galaxies that has been summarized also for us lay people in the APOD site
The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. The combined image data also reveal the galaxy's young blue star clusters and telltale pinkish star forming regions. And remarkably apparent in NGC 891's edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also be seen near this galaxy's disk.